Release: 2.0.42 | Release Date: July 29, 2025

# SQLAlchemy 2.0 Documentation

# 0.8 Changelog

## 0.8.7

Released: July 22, 2014

### orm

- [orm] [bug]

  Fixed bug in subquery eager loading where a long chain of eager loads across a polymorphic-subclass boundary in conjunction with polymorphic loading would fail to locate the subclass-link in the chain, erroring out with a missing property name on an `AliasedClass`.

  References: #3055

- [orm] [bug]

  Fixed ORM bug where the `class_mapper()` function would mask AttributeErrors or KeyErrors that should raise during mapper configuration due to user errors. The catch for attribute/keyerror has been made more specific to not include the configuration step.

  References: #3047

### sql

- [sql] [bug]

  Fixed bug in `Enum` and other `SchemaType` subclasses where direct association of the type with a `MetaData` would lead to a hang when events (like create events) were emitted on the `MetaData`.

  References: #3124

- [sql] [bug]

  Fixed a bug within the custom operator plus `TypeEngine.with_variant()` system, whereby using a `TypeDecorator` in conjunction with variant would fail with an MRO error when a comparison operator was used.

  References: #3102

- [sql] [bug]

  Fixed bug in INSERT..FROM SELECT construct where selecting from a UNION would wrap the union in an anonymous (e.g. unlabeled) subquery.

  References: #3044

- [sql] [bug]

  Fixed bug where `Table.update()` and `Table.delete()` would produce an empty WHERE clause when an empty `and_()` or `or_()` or other blank expression were applied. This is now consistent with that of `select()`.

  References: #3045

### postgresql

- [postgresql] [bug]

  Added the `hashable=False` flag to the PG `HSTORE` type, which is needed to allow the ORM to skip over trying to “hash” an ORM-mapped HSTORE column when requesting it in a mixed column/entity list. Patch courtesy Gunnlaugur Þór Briem.

  References: #3053

- [postgresql] [bug]

  Added a new “disconnect” message “connection has been closed unexpectedly”. This appears to be related to newer versions of SSL. Pull request courtesy Antti Haapala.

### mysql

- [mysql] [bug]

  MySQL error 2014 “commands out of sync” appears to be raised as a ProgrammingError, not OperationalError, in modern MySQL-Python versions; all MySQL error codes that are tested for “is disconnect” are now checked within OperationalError and ProgrammingError regardless.

  References: #3101

- [mysql] [bug]

  Fixed bug where column names added to `mysql_length` parameter on an index needed to have the same quoting for quoted names in order to be recognized. The fix makes the quotes optional but also provides the old behavior for backwards compatibility with those using the workaround.

  References: #3085

- [mysql] [bug]

  Added support for reflecting tables where an index includes KEY_BLOCK_SIZE using an equal sign. Pull request courtesy Sean McGivern.

### mssql

- [mssql] [bug]

  Added statement encoding to the “SET IDENTITY_INSERT” statements which operate when an explicit INSERT is being interjected into an IDENTITY column, to support non-ascii table identifiers on drivers such as pyodbc + unix + py2k that don’t support unicode statements.

- [mssql] [bug]

  In the SQL Server pyodbc dialect, repaired the implementation for the `description_encoding` dialect parameter, which when not explicitly set was preventing cursor.description from being parsed correctly in the case of result sets that contained names in alternate encodings. This parameter shouldn’t be needed going forward.

  References: #3091

### misc

- [bug] [declarative]

  The `__mapper_args__` dictionary is copied from a declarative mixin or abstract class when accessed, so that modifications made to this dictionary by declarative itself won’t conflict with that of other mappings. The dictionary is modified regarding the `version_id_col` and `polymorphic_on` arguments, replacing the column within with the one that is officially mapped to the local class/table.

  References: #3062

- [bug] [ext]

  Fixed bug in mutable extension where `MutableDict` did not report change events for the `setdefault()` dictionary operation.

  References: #3051, #3093

- [bug] [ext]

  Fixed bug where `MutableDict.setdefault()` didn’t return the existing or new value (this bug was not released in any 0.8 version). Pull request courtesy Thomas Hervé.

  References: #3051, #3093

## 0.8.6

Released: March 28, 2014

### general

- [general] [bug]

  Adjusted `setup.py` file to support the possible future removal of the `setuptools.Feature` extension from setuptools. If this keyword isn’t present, the setup will still succeed with setuptools rather than falling back to distutils. C extension building can be disabled now also by setting the DISABLE_SQLALCHEMY_CEXT environment variable. This variable works whether or not setuptools is even available.

  References: #2986

### orm

- [orm] [bug]

  Fixed ORM bug where changing the primary key of an object, then marking it for DELETE would fail to target the correct row for DELETE.

  References: #3006

- [orm] [bug]

  Fixed regression from 0.8.3 as a result of #2818 where `Query.exists()` wouldn’t work on a query that only had a `Query.select_from()` entry but no other entities.

  References: #2995

- [orm] [bug]

  Improved an error message which would occur if a query() were made against a non-selectable, such as a `literal_column()`, and then an attempt was made to use `Query.join()` such that the “left” side would be determined as `None` and then fail. This condition is now detected explicitly.

- [orm] [bug]

  Removed stale names from `sqlalchemy.orm.interfaces.__all__` and refreshed with current names, so that an `import *` from this module again works.

  References: #2975

### sql

- [sql] [bug]

  Fixed bug in `tuple_()` construct where the “type” of essentially the first SQL expression would be applied as the “comparison type” to a compared tuple value; this has the effect in some cases of an inappropriate “type coercion” occurring, such as when a tuple that has a mix of String and Binary values improperly coerces target values to Binary even though that’s not what they are on the left side. `tuple_()` now expects heterogeneous types within its list of values.

  References: #2977

### postgresql

- [postgresql] [feature]

  Enabled “sane multi-row count” checking for the psycopg2 DBAPI, as this seems to be supported as of psycopg2 2.0.9.

- [postgresql] [bug]

  Fixed regression caused by release 0.8.5 / 0.9.3’s compatibility enhancements where index reflection on PostgreSQL versions specific to only the 8.1, 8.2 series again broke, surrounding the ever problematic int2vector type. While int2vector supports array operations as of 8.1, apparently it only supports CAST to a varchar as of 8.3.

  References: #3000

### misc

- [bug] [ext]

  Fixed bug in mutable extension as well as `flag_modified()` where the change event would not be propagated if the attribute had been reassigned to itself.

  References: #2997

## 0.8.5

Released: February 19, 2014

### orm

- [orm] [bug]

  Fixed bug where `Query.get()` would fail to consistently raise the `InvalidRequestError` that invokes when called on a query with existing criterion, when the given identity is already present in the identity map.

  References: #2951

- [orm] [bug]

  Fixed error message when an iterator object is passed to `class_mapper()` or similar, where the error would fail to render on string formatting. Pullreq courtesy Kyle Stark.

- [orm] [bug]

  An adjustment to the `subqueryload()` strategy which ensures that the query runs after the loading process has begun; this is so that the subqueryload takes precedence over other loaders that may be hitting the same attribute due to other eager/noload situations at the wrong time.

  References: #2887

- [orm] [bug]

  Fixed bug when using joined table inheritance from a table to a select/alias on the base, where the PK columns were also not same named; the persistence system would fail to copy primary key values from the base table to the inherited table upon INSERT.

  References: #2885

- [orm] [bug]

  `composite()` will raise an informative error message when the columns/attribute (names) passed don’t resolve to a Column or mapped attribute (such as an erroneous tuple); previously raised an unbound local.

  References: #2889

### engine

- [engine] [bug] [pool]

  Fixed a critical regression caused by #2880 where the newly concurrent ability to return connections from the pool means that the “first_connect” event is now no longer synchronized either, thus leading to dialect mis-configurations under even minimal concurrency situations.

  References: #2880, #2964

### sql

- [sql] [bug]

  Fixed bug where calling `Insert.values()` with an empty list or tuple would raise an IndexError. It now produces an empty insert construct as would be the case with an empty dictionary.

  References: #2944

- [sql] [bug]

  Fixed bug where `ColumnOperators.in_()` would go into an endless loop if erroneously passed a column expression whose comparator included the `__getitem__()` method, such as a column that uses the `ARRAY` type.

  References: #2957

- [sql] [bug]

  Fixed issue where a primary key column that has a Sequence on it, yet the column is not the “auto increment” column, either because it has a foreign key constraint or `autoincrement=False` set, would attempt to fire the Sequence on INSERT for backends that don’t support sequences, when presented with an INSERT missing the primary key value. This would take place on non-sequence backends like SQLite, MySQL.

  References: #2896

- [sql] [bug]

  Fixed bug with `Insert.from_select()` method where the order of the given names would not be taken into account when generating the INSERT statement, thus producing a mismatch versus the column names in the given SELECT statement. Also noted that `Insert.from_select()` implies that Python-side insert defaults cannot be used, since the statement has no VALUES clause.

  References: #2895

- [sql] [enhancement]

  The exception raised when a `BindParameter` is present in a compiled statement without a value now includes the key name of the bound parameter in the error message.

### postgresql

- [postgresql] [bug]

  Added an additional message to psycopg2 disconnect detection, “could not send data to server”, which complements the existing “could not receive data from server” and has been observed by users.

  References: #2936

- [postgresql] [bug]

  > Support has been improved for PostgreSQL reflection behavior on very old (pre 8.1) versions of PostgreSQL, and potentially other PG engines such as Redshift (assuming Redshift reports the version as < 8.1). The query for “indexes” as well as “primary keys” relies upon inspecting a so-called “int2vector” datatype, which refuses to coerce to an array prior to 8.1 causing failures regarding the “ANY()” operator used in the query. Extensive googling has located the very hacky, but recommended-by-PG-core-developer query to use when PG version < 8.1 is in use, so index and primary key constraint reflection now work on these versions.

- [postgresql] [bug]

  Revised this very old issue where the PostgreSQL “get primary key” reflection query were updated to take into account primary key constraints that were renamed; the newer query fails on very old versions of PostgreSQL such as version 7, so the old query is restored in those cases when server_version_info < (8, 0) is detected.

  References: #2291

### mysql

- [mysql] [feature]

  Added new MySQL-specific `DATETIME` which includes fractional seconds support; also added fractional seconds support to `TIMESTAMP`. DBAPI support is limited, though fractional seconds are known to be supported by MySQL Connector/Python. Patch courtesy Geert JM Vanderkelen.

  References: #2941

- [mysql] [bug]

  Added support for the `PARTITION BY` and `PARTITIONS` MySQL table keywords, specified as `mysql_partition_by='value'` and `mysql_partitions='value'` to `Table`. Pull request courtesy Marcus McCurdy.

  References: #2966

- [mysql] [bug]

  Fixed bug which prevented MySQLdb-based dialects (e.g. pymysql) from working in Py3K, where a check for “connection charset” would fail due to Py3K’s more strict value comparison rules. The call in question wasn’t taking the database version into account in any case as the server version was still None at that point, so the method overall has been simplified to rely upon connection.character_set_name().

  References: #2933

- [mysql] [bug]

  Some missing methods added to the cymysql dialect, including _get_server_version_info() and _detect_charset(). Pullreq courtesy Hajime Nakagami.

### sqlite

- [sqlite] [bug]

  Restored a change that was missed in the backport of unique constraint reflection to 0.8, where `UniqueConstraint` with SQLite would fail if reserved keywords were included in the names of columns. Pull request courtesy Roman Podolyaka.

### mssql

- [mssql] [bug] [firebird]

  The “asdecimal” flag used with the `Float` type will now work with Firebird as well as the mssql+pyodbc dialects; previously the decimal conversion was not occurring.

- [mssql] [bug] [pymssql]

  Added “Net-Lib error during Connection reset by peer” message to the list of messages checked for “disconnect” within the pymssql dialect. Courtesy John Anderson.

### misc

- [bug] [py3k]

  Fixed Py3K bug where a missing import would cause “literal binary” mode to fail to import “util.binary_type” when rendering a bound parameter. 0.9 handles this differently. Pull request courtesy Andreas Zeidler.

- [bug] [firebird]

  The firebird dialect will quote identifiers which begin with an underscore. Courtesy Treeve Jelbert.

  References: #2897

- [bug] [firebird]

  Fixed bug in Firebird index reflection where the columns within the index were not sorted correctly; they are now sorted in order of RDB$FIELD_POSITION.

- [bug] [declarative]

  Error message when a string arg sent to `relationship()` which doesn’t resolve to a class or mapper has been corrected to work the same way as when a non-string arg is received, which indicates the name of the relationship which had the configurational error.

  References: #2888

## 0.8.4

Released: December 8, 2013

### orm

- [orm] [bug]

  Fixed a regression introduced by #2818 where the EXISTS query being generated would produce a “columns being replaced” warning for a statement with two same-named columns, as the internal SELECT wouldn’t have use_labels set.

  References: #2818

### engine

- [engine] [bug]

  A DBAPI that raises an error on `connect()` which is not a subclass of dbapi.Error (such as `TypeError`, `NotImplementedError`, etc.) will propagate the exception unchanged. Previously, the error handling specific to the `connect()` routine would both inappropriately run the exception through the dialect’s `Dialect.is_disconnect()` routine as well as wrap it in a `sqlalchemy.exc.DBAPIError`. It is now propagated unchanged in the same way as occurs within the execute process.

  References: #2881

- [engine] [bug] [pool]

  The `QueuePool` has been enhanced to not block new connection attempts when an existing connection attempt is blocking. Previously, the production of new connections was serialized within the block that monitored overflow; the overflow counter is now altered within its own critical section outside of the connection process itself.

  References: #2880

- [engine] [bug] [pool]

  Made a slight adjustment to the logic which waits for a pooled connection to be available, such that for a connection pool with no timeout specified, it will every half a second break out of the wait to check for the so-called “abort” flag, which allows the waiter to break out in case the whole connection pool was dumped; normally the waiter should break out due to a notify_all() but it’s possible this notify_all() is missed in very slim cases. This is an extension of logic first introduced in 0.8.0, and the issue has only been observed occasionally in stress tests.

  References: #2522

- [engine] [bug]

  Fixed bug where SQL statement would be improperly ASCII-encoded when a pre-DBAPI `StatementError` were raised within `Connection.execute()`, causing encoding errors for non-ASCII statements. The stringification now remains within Python unicode thus avoiding encoding errors.

  References: #2871

### sql

- [sql] [feature]

  Added support for “unique constraint” reflection, via the `Inspector.get_unique_constraints()` method. Thanks for Roman Podolyaka for the patch.

  References: #1443

### postgresql

- [postgresql] [bug]

  Fixed bug where index reflection would mis-interpret indkey values when using the pypostgresql adapter, which returns these values as lists vs. psycopg2’s return type of string.

  References: #2855

### mssql

- [mssql] [bug]

  Fixed bug introduced in 0.8.0 where the `DROP INDEX` statement for an index in MSSQL would render incorrectly if the index were in an alternate schema; the schemaname/tablename would be reversed. The format has been also been revised to match current MSSQL documentation. Courtesy Derek Harland.

### oracle

- [oracle] [bug]

  Added ORA-02396 “maximum idle time” error code to list of “is disconnect” codes with cx_oracle.

  References: #2864

- [oracle] [bug]

  Fixed bug where Oracle `VARCHAR` types given with no length (e.g. for a `CAST` or similar) would incorrectly render `None CHAR` or similar.

  References: #2870

### misc

- [bug] [ext]

  Fixed bug which prevented the `serializer` extension from working correctly with table or column names that contain non-ASCII characters.

  References: #2869

## 0.8.3

Released: October 26, 2013

### orm

- [orm] [feature]

  Added new option to `relationship()` `distinct_target_key`. This enables the subquery eager loader strategy to apply a DISTINCT to the innermost SELECT subquery, to assist in the case where duplicate rows are generated by the innermost query which corresponds to this relationship (there’s not yet a general solution to the issue of dupe rows within subquery eager loading, however, when joins outside of the innermost subquery produce dupes). When the flag is set to `True`, the DISTINCT is rendered unconditionally, and when it is set to `None`, DISTINCT is rendered if the innermost relationship targets columns that do not comprise a full primary key. The option defaults to False in 0.8 (e.g. off by default in all cases), None in 0.9 (e.g. automatic by default). Thanks to Alexander Koval for help with this.

  See also

  Subquery Eager Loading will apply DISTINCT to the innermost SELECT for some queries

  References: #2836

- [orm] [bug]

  Fixed bug where list instrumentation would fail to represent a setslice of `[0:0]` correctly, which in particular could occur when using `insert(0, item)` with the association proxy. Due to some quirk in Python collections, the issue was much more likely with Python 3 rather than 2.

  This change is also backported to: 0.7.11

  References: #2807

- [orm] [bug]

  Fixed bug where using an annotation such as `remote()` or `foreign()` on a `Column` before association with a parent `Table` could produce issues related to the parent table not rendering within joins, due to the inherent copy operation performed by an annotation.

  References: #2813

- [orm] [bug]

  Fixed bug where `Query.exists()` failed to work correctly without any WHERE criterion. Courtesy Vladimir Magamedov.

  References: #2818

- [orm] [bug]

  Backported a change from 0.9 whereby the iteration of a hierarchy of mappers used in polymorphic inheritance loads is sorted, which allows the SELECT statements generated for polymorphic queries to have deterministic rendering, which in turn helps with caching schemes that cache on the SQL string itself.

  References: #2779

- [orm] [bug]

  Fixed a potential issue in an ordered sequence implementation used by the ORM to iterate mapper hierarchies; under the Jython interpreter this implementation wasn’t ordered, even though cPython and PyPy maintained ordering.

  References: #2794

- [orm] [bug]

  Fixed bug in ORM-level event registration where the “raw” or “propagate” flags could potentially be mis-configured in some “unmapped base class” configurations.

  References: #2786

- [orm] [bug]

  A performance fix related to the usage of the `defer()` option when loading mapped entities. The function overhead of applying a per-object deferred callable to an instance at load time was significantly higher than that of just loading the data from the row (note that `defer()` is meant to reduce DB/network overhead, not necessarily function call count); the function call overhead is now less than that of loading data from the column in all cases. There is also a reduction in the number of “lazy callable” objects created per load from N (total deferred values in the result) to 1 (total number of deferred cols).

  References: #2778

- [orm] [bug]

  Fixed bug whereby attribute history functions would fail when an object we moved from “persistent” to “pending” using the `make_transient()` function, for operations involving collection-based backrefs.

  References: #2773

### orm declarative

- [orm] [declarative] [feature]

  Added a convenience class decorator `as_declarative()`, is a wrapper for `declarative_base()` which allows an existing base class to be applied using a nifty class-decorated approach.

### examples

- [examples] [feature]

  Improved the examples in `examples/generic_associations`, including that `discriminator_on_association.py` makes use of single table inheritance do the work with the “discriminator”. Also added a true “generic foreign key” example, which works similarly to other popular frameworks in that it uses an open-ended integer to point to any other table, foregoing traditional referential integrity. While we don’t recommend this pattern, information wants to be free.

- [examples] [bug]

  Added “autoincrement=False” to the history table created in the versioning example, as this table shouldn’t have autoinc on it in any case, courtesy Patrick Schmid.

### engine

- [engine] [feature]

  `repr()` for the `URL` of an `Engine` will now conceal the password using asterisks. Courtesy Gunnlaugur Þór Briem.

  References: #2821

- [engine] [bug]

  The regexp used by the `make_url()` function now parses ipv6 addresses, e.g. surrounded by brackets.

  This change is also backported to: 0.7.11

  References: #2851

- [engine] [bug] [oracle]

  Dialect.initialize() is not called a second time if an `Engine` is recreated, due to a disconnect error. This fixes a particular issue in the Oracle 8 dialect, but in general the dialect.initialize() phase should only be once per dialect.

  References: #2776

- [engine] [bug] [pool]

  Fixed bug where `QueuePool` would lose the correct checked out count if an existing pooled connection failed to reconnect after an invalidate or recycle event.

  References: #2772

### sql

- [sql] [feature]

  Added new method to the `insert()` construct `Insert.from_select()`. Given a list of columns and a selectable, renders `INSERT INTO (table) (columns) SELECT ..`.

  References: #722

- [sql] [feature]

  The `update()`, `insert()`, and `delete()` constructs will now interpret ORM entities as target tables to be operated upon, e.g.:

      from sqlalchemy import insert, update, delete

      ins = insert(SomeMappedClass).values(x=5)

      del_ = delete(SomeMappedClass).where(SomeMappedClass.id == 5)

      upd = update(SomeMappedClass).where(SomeMappedClass.id == 5).values(name="ed")

- [sql] [bug]

  Fixed regression dating back to 0.7.9 whereby the name of a CTE might not be properly quoted if it was referred to in multiple FROM clauses.

  This change is also backported to: 0.7.11

  References: #2801

- [sql] [bug] [cte]

  Fixed bug in common table expression system where if the CTE were used only as an `alias()` construct, it would not render using the WITH keyword.

  This change is also backported to: 0.7.11

  References: #2783

- [sql] [bug]

  Fixed bug in `CheckConstraint` DDL where the “quote” flag from a `Column` object would not be propagated.

  This change is also backported to: 0.7.11

  References: #2784

- [sql] [bug]

  Fixed bug where `type_coerce()` would not interpret ORM elements with a `__clause_element__()` method properly.

  References: #2849

- [sql] [bug]

  The `Enum` and `Boolean` types now bypass any custom (e.g. TypeDecorator) type in use when producing the CHECK constraint for the “non native” type. This so that the custom type isn’t involved in the expression within the CHECK, since this expression is against the “impl” value and not the “decorated” value.

  References: #2842

- [sql] [bug]

  The `.unique` flag on `Index` could be produced as `None` if it was generated from a `Column` that didn’t specify `unique` (where it defaults to `None`). The flag will now always be `True` or `False`.

  References: #2825

- [sql] [bug]

  Fixed bug in default compiler plus those of postgresql, mysql, and mssql to ensure that any literal SQL expression values are rendered directly as literals, instead of as bound parameters, within a CREATE INDEX statement. This also changes the rendering scheme for other DDL such as constraints.

  References: #2742

- [sql] [bug]

  A `select()` that is made to refer to itself in its FROM clause, typically via in-place mutation, will raise an informative error message rather than causing a recursion overflow.

  References: #2815

- [sql] [bug]

  Non-working “schema” argument on `ForeignKey` is deprecated; raises a warning. Removed in 0.9.

  References: #2831

- [sql] [bug]

  Fixed bug where using the `column_reflect` event to change the `.key` of the incoming `Column` would prevent primary key constraints, indexes, and foreign key constraints from being correctly reflected.

  References: #2811

- [sql] [bug]

  The `ColumnOperators.notin_()` operator added in 0.8 now properly produces the negation of the expression “IN” returns when used against an empty collection.

- [sql] [bug] [postgresql]

  Fixed bug where the expression system relied upon the `str()` form of a some expressions when referring to the `.c` collection on a `select()` construct, but the `str()` form isn’t available since the element relies on dialect-specific compilation constructs, notably the `__getitem__()` operator as used with a PostgreSQL `ARRAY` element. The fix also adds a new exception class `UnsupportedCompilationError` which is raised in those cases where a compiler is asked to compile something it doesn’t know how to.

  References: #2780

### postgresql

- [postgresql] [bug]

  Removed a 128-character truncation from the reflection of the server default for a column; this code was original from PG system views which truncated the string for readability.

  References: #2844

- [postgresql] [bug]

  Parenthesis will be applied to a compound SQL expression as rendered in the column list of a CREATE INDEX statement.

  References: #2742

- [postgresql] [bug]

  Fixed bug where PostgreSQL version strings that had a prefix preceding the words “PostgreSQL” or “EnterpriseDB” would not parse. Courtesy Scott Schaefer.

  References: #2819

### mysql

- [mysql] [bug]

  Updates to MySQL reserved words for versions 5.5, 5.6, courtesy Hanno Schlichting.

  This change is also backported to: 0.7.11

  References: #2791

- [mysql] [bug]

  The change in #2721, which is that the `deferrable` keyword of `ForeignKeyConstraint` is silently ignored on the MySQL backend, will be reverted as of 0.9; this keyword will now render again, raising errors on MySQL as it is not understood - the same behavior will also apply to the `initially` keyword. In 0.8, the keywords will remain ignored but a warning is emitted. Additionally, the `match` keyword now raises a `CompileError` on 0.9 and emits a warning on 0.8; this keyword is not only silently ignored by MySQL but also breaks the ON UPDATE/ON DELETE options.

  To use a `ForeignKeyConstraint` that does not render or renders differently on MySQL, use a custom compilation option. An example of this usage has been added to the documentation, see MySQL / MariaDB Foreign Keys.

  References: #2721, #2839

- [mysql] [bug]

  MySQL-connector dialect now allows options in the create_engine query string to override those defaults set up in the connect, including “buffered” and “raise_on_warnings”.

  References: #2515

### sqlite

- [sqlite] [bug]

  The newly added SQLite DATETIME arguments storage_format and regexp apparently were not fully implemented correctly; while the arguments were accepted, in practice they would have no effect; this has been fixed.

  References: #2781

### oracle

- [oracle] [bug]

  Fixed bug where Oracle table reflection using synonyms would fail if the synonym and the table were in different remote schemas. Patch to fix courtesy Kyle Derr.

  References: #2853

### misc

- [feature]

  Added a new flag `system=True` to `Column`, which marks the column as a “system” column which is automatically made present by the database (such as PostgreSQL `oid` or `xmin`). The column will be omitted from the `CREATE TABLE` statement but will otherwise be available for querying. In addition, the `CreateColumn` construct can be applied to a custom compilation rule which allows skipping of columns, by producing a rule that returns `None`.

## 0.8.2

Released: July 3, 2013

### orm

- [orm] [feature]

  Added a new method `Query.select_entity_from()` which will in 0.9 replace part of the functionality of `Query.select_from()`. In 0.8, the two methods perform the same function, so that code can be migrated to use the `Query.select_entity_from()` method as appropriate. See the 0.9 migration guide for details.

  References: #2736

- [orm] [bug]

  A warning is emitted when trying to flush an object of an inherited class where the polymorphic discriminator has been assigned to a value that is invalid for the class.

  References: #2750

- [orm] [bug]

  Fixed bug in polymorphic SQL generation where multiple joined-inheritance entities against the same base class joined to each other as well would not track columns on the base table independently of each other if the string of joins were more than two entities long.

  References: #2759

- [orm] [bug]

  Fixed bug where sending a composite attribute into `Query.order_by()` would produce a parenthesized expression not accepted by some databases.

  References: #2754

- [orm] [bug]

  Fixed the interaction between composite attributes and the `aliased()` function. Previously, composite attributes wouldn’t work correctly in comparison operations when aliasing was applied.

  References: #2755

- [orm] [bug] [ext]

  Fixed bug where `MutableDict` didn’t report a change event when `clear()` was called.

  References: #2730

- [orm] [bug]

  Fixed a regression caused by #2682 whereby the evaluation invoked by `Query.update()` and `Query.delete()` would hit upon unsupported `True` and `False` symbols which now appear due to the usage of `IS`.

  References: #2737

- [orm] [bug]

  Fixed a regression from 0.7 caused by this ticket, which made the check for recursion overflow in self-referential eager joining too loose, missing a particular circumstance where a subclass had lazy=”joined” or “subquery” configured and the load was a “with_polymorphic” against the base.

  References: #2481

- [orm] [bug]

  Fixed a regression from 0.7 where the contextmanager feature of `Session.begin_nested()` would fail to correctly roll back the transaction when a flush error occurred, instead raising its own exception while leaving the session still pending a rollback.

  References: #2718

### orm declarative

- [orm] [declarative] [feature]

  ORM descriptors such as hybrid properties can now be referenced by name in a string argument used with `order_by`, `primaryjoin`, or similar in `relationship()`, in addition to column-bound attributes.

  References: #2761

### examples

- [examples] [bug]

  Fixed an issue with the “versioning” recipe whereby a many-to-one reference could produce a meaningless version for the target, even though it was not changed, when backrefs were present. Patch courtesy Matt Chisholm.

- [examples] [bug]

  Fixed a small bug in the dogpile example where the generation of SQL cache keys wasn’t applying deduping labels to the statement the same way `Query` normally does.

### engine

- [engine] [bug]

  Fixed bug where the `reset_on_return` argument to various `Pool` implementations would not be propagated when the pool was regenerated. Courtesy Eevee.

- [engine] [bug] [sybase]

  Fixed a bug where the routine to detect the correct kwargs being sent to `create_engine()` would fail in some cases, such as with the Sybase dialect.

  References: #2732

### sql

- [sql] [feature]

  Provided a new attribute for `TypeDecorator` called `TypeDecorator.coerce_to_is_types`, to make it easier to control how comparisons using `==` or `!=` to `None` and boolean types goes about producing an `IS` expression, or a plain equality expression with a bound parameter.

  References: #2734, #2744

- [sql] [bug]

  Multiple fixes to the correlation behavior of `Select` constructs, first introduced in 0.8.0:

  - To satisfy the use case where FROM entries should be correlated outwards to a SELECT that encloses another, which then encloses this one, correlation now works across multiple levels when explicit correlation is established via `Select.correlate()`, provided that the target select is somewhere along the chain contained by a WHERE/ORDER BY/columns clause, not just nested FROM clauses. This makes `Select.correlate()` act more compatibly to that of 0.7 again while still maintaining the new “smart” correlation.

  - When explicit correlation is not used, the usual “implicit” correlation limits its behavior to just the immediate enclosing SELECT, to maximize compatibility with 0.7 applications, and also prevents correlation across nested FROMs in this case, maintaining compatibility with 0.8.0/0.8.1.

  - The `Select.correlate_except()` method was not preventing the given FROM clauses from correlation in all cases, and also would cause FROM clauses to be incorrectly omitted entirely (more like what 0.7 would do), this has been fixed.

  - Calling select.correlate_except(None) will enter all FROM clauses into correlation as would be expected.

  References: #2668, #2746

- [sql] [bug]

  Fixed bug whereby joining a select() of a table “A” with multiple foreign key paths to a table “B”, to that table “B”, would fail to produce the “ambiguous join condition” error that would be reported if you join table “A” directly to “B”; it would instead produce a join condition with multiple criteria.

  References: #2738

- [sql] [bug] [reflection]

  Fixed bug whereby using `MetaData.reflect()` across a remote schema as well as a local schema could produce wrong results in the case where both schemas had a table of the same name.

  References: #2728

- [sql] [bug]

  Removed the “not implemented” `__iter__()` call from the base `ColumnOperators` class, while this was introduced in 0.8.0 to prevent an endless, memory-growing loop when one also implements a `__getitem__()` method on a custom operator and then calls erroneously `list()` on that object, it had the effect of causing column elements to report that they were in fact iterable types which then throw an error when you try to iterate. There’s no real way to have both sides here so we stick with Python best practices. Careful with implementing `__getitem__()` on your custom operators!

  References: #2726

- [sql] [bug] [mssql]

  Regression from this ticket caused the unsupported keyword “true” to render, added logic to convert this to 1/0 for SQL server.

  References: #2682

### postgresql

- [postgresql] [feature]

  Support for PostgreSQL 9.2 range types has been added. Currently, no type translation is provided, so works directly with strings or psycopg2 2.5 range extension types at the moment. Patch courtesy Chris Withers.

- [postgresql] [feature]

  Added support for “AUTOCOMMIT” isolation when using the psycopg2 DBAPI. The keyword is available via the `isolation_level` execution option. Patch courtesy Roman Podolyaka.

  References: #2072

- [postgresql] [bug]

  The behavior of `extract()` has been simplified on the PostgreSQL dialect to no longer inject a hardcoded `::timestamp` or similar cast into the given expression, as this interfered with types such as timezone-aware datetimes, but also does not appear to be at all necessary with modern versions of psycopg2.

  References: #2740

- [postgresql] [bug]

  Fixed bug in HSTORE type where keys/values that contained backslashed quotes would not be escaped correctly when using the “non native” (i.e. non-psycopg2) means of translating HSTORE data. Patch courtesy Ryan Kelly.

  References: #2766

- [postgresql] [bug]

  Fixed bug where the order of columns in a multi-column PostgreSQL index would be reflected in the wrong order. Courtesy Roman Podolyaka.

  References: #2767

- [postgresql] [bug]

  Fixed the HSTORE type to correctly encode/decode for unicode. This is always on, as the hstore is a textual type, and matches the behavior of psycopg2 when using Python 3. Courtesy Dmitry Mugtasimov.

  References: #2735

### mysql

- [mysql] [feature]

  The `mysql_length` parameter used with `Index` can now be passed as a dictionary of column names/lengths, for use with composite indexes. Big thanks to Roman Podolyaka for the patch.

  References: #2704

- [mysql] [bug]

  Fixed bug when using multi-table UPDATE where a supplemental table is a SELECT with its own bound parameters, where the positioning of the bound parameters would be reversed versus the statement itself when using MySQL’s special syntax.

  References: #2768

- [mysql] [bug]

  Added another conditional to the `mysql+gaerdbms` dialect to detect so-called “development” mode, where we should use the `rdbms_mysqldb` DBAPI. Patch courtesy Brett Slatkin.

  References: #2715

- [mysql] [bug]

  The `deferrable` keyword argument on `ForeignKey` and `ForeignKeyConstraint` will not render the `DEFERRABLE` keyword on the MySQL dialect. For a long time we left this in place because a non-deferrable foreign key would act very differently than a deferrable one, but some environments just disable FKs on MySQL, so we’ll be less opinionated here.

  References: #2721

- [mysql] [bug]

  Updated mysqlconnector dialect to check for disconnect based on the apparent string message sent in the exception; tested against mysqlconnector 1.0.9.

### sqlite

- [sqlite] [bug]

  Added `sqlalchemy.types.BIGINT` to the list of type names that can be reflected by the SQLite dialect; courtesy Russell Stuart.

  References: #2764

### mssql

- [mssql] [bug]

  When querying the information schema on SQL Server 2000, removed a CAST call that was added in 0.8.1 to help with driver issues, which apparently is not compatible on 2000. The CAST remains in place for SQL Server 2005 and greater.

  References: #2747

### misc

- [feature] [firebird]

  Added new flag `retaining=True` to the kinterbasdb and fdb dialects. This controls the value of the `retaining` flag sent to the `commit()` and `rollback()` methods of the DBAPI connection. Due to historical concerns, this flag defaults to `True` in 0.8.2, however in 0.9.0b1 this flag defaults to `False`.

  References: #2763

- [bug] [firebird]

  Type lookup when reflecting the Firebird types LONG and INT64 has been fixed so that LONG is treated as INTEGER, INT64 treated as BIGINT, unless the type has a “precision” in which case it’s treated as NUMERIC. Patch courtesy Russell Stuart.

  References: #2757

- [bug] [ext]

  Fixed bug whereby if a composite type were set up with a function instead of a class, the mutable extension would trip up when it tried to check that column for being a `MutableComposite` (which it isn’t). Courtesy asldevi.

- [requirements]

  The Python mock library is now required in order to run the unit test suite. While part of the standard library as of Python 3.3, previous Python installations will need to install this in order to run unit tests or to use the `sqlalchemy.testing` package for external dialects.

## 0.8.1

Released: April 27, 2013

### orm

- [orm] [feature]

  Added a convenience method to Query that turns a query into an EXISTS subquery of the form `EXISTS (SELECT 1 FROM ... WHERE ...)`.

  References: #2673

- [orm] [bug]

  Fixed bug when a query of the form: `query(SubClass).options(subqueryload(Baseclass.attrname))`, where `SubClass` is a joined inh of `BaseClass`, would fail to apply the `JOIN` inside the subquery on the attribute load, producing a cartesian product. The populated results still tended to be correct as additional rows are just ignored, so this issue may be present as a performance degradation in applications that are otherwise working correctly.

  This change is also backported to: 0.7.11

  References: #2699

- [orm] [bug]

  Fixed bug in unit of work whereby a joined-inheritance subclass could insert the row for the “sub” table before the parent table, if the two tables had no ForeignKey constraints set up between them.

  This change is also backported to: 0.7.11

  References: #2689

- [orm] [bug]

  Fixes to the `sqlalchemy.ext.serializer` extension, including that the “id” passed from the pickler is turned into a string to prevent against bytes being parsed on Py3K, as well as that `relationship()` and `orm.join()` constructs are now properly serialized.

  References: #2698

- [orm] [bug]

  A significant improvement to the inner workings of query.join(), such that the decisionmaking involved on how to join has been dramatically simplified. New test cases now pass such as multiple joins extending from the middle of an already complex series of joins involving inheritance and such. Joining from deeply nested subquery structures is still complicated and not without caveats, but with these improvements the edge cases are hopefully pushed even farther out to the edges.

  References: #2714

- [orm] [bug]

  Added a conditional to the unpickling process for ORM mapped objects, such that if the reference to the object were lost when the object was pickled, we don’t erroneously try to set up _sa_instance_state - fixes a NoneType error.

- [orm] [bug]

  Fixed bug where many-to-many relationship with uselist=False would fail to delete the association row and raise an error if the scalar attribute were set to None. This was a regression introduced by the changes for #2229.

  References: #2710

- [orm] [bug]

  Improved the behavior of instance management regarding the creation of strong references within the Session; an object will no longer have an internal reference cycle created if it’s in the transient state or moves into the detached state - the strong ref is created only when the object is attached to a Session and is removed when the object is detached. This makes it somewhat safer for an object to have a __del__() method, even though this is not recommended, as relationships with backrefs produce cycles too. A warning has been added when a class with a __del__() method is mapped.

  References: #2708

- [orm] [bug]

  Fixed bug whereby ORM would run the wrong kind of query when refreshing an inheritance-mapped class where the superclass was mapped to a non-Table object, like a custom join() or a select(), running a query that assumed a hierarchy that’s mapped to individual Table-per-class.

  References: #2697

- [orm] [bug]

  Fixed __repr__() on mapper property constructs to work before the object is initialized, so that Sphinx builds with recent Sphinx versions can read them.

### orm declarative

- [orm] [declarative] [bug]

  Fixed indirect regression regarding `has_inherited_table()`, where since it considers the current class’ `__table__`, was sensitive to when it was called. This is 0.7’s behavior also, but in 0.7 things tended to “work out” within events like `__mapper_args__()`. `has_inherited_table()` now only considers superclasses, so should return the same answer regarding the current class no matter when it’s called (obviously assuming the state of the superclass).

  References: #2656

### examples

- [examples] [bug]

  Fixed a long-standing bug in the caching example, where the limit/offset parameter values wouldn’t be taken into account when computing the cache key. The _key_from_query() function has been simplified to work directly from the final compiled statement in order to get at both the full statement as well as the fully processed parameter list.

### sql

- [sql] [feature]

  Loosened the check on dialect-specific argument names passed to Table(); since we want to support external dialects and also want to support args without a certain dialect being installed, it only checks the format of the arg now, rather than looking for that dialect in sqlalchemy.dialects.

- [sql] [bug] [mysql]

  Fully implemented the IS and IS NOT operators with regards to the True/False constants. An expression like `col.is_(True)` will now render `col IS true` on the target platform, rather than converting the True/ False constant to an integer bound parameter. This allows the `is_()` operator to work on MySQL when given True/False constants.

  References: #2682

- [sql] [bug]

  A major fix to the way in which a select() object produces labeled columns when apply_labels() is used; this mode produces a SELECT where each column is labeled as in <tablename>_<columnname>, to remove column name collisions for a multiple table select. The fix is that if two labels collide when combined with the table name, i.e. “foo.bar_id” and “foo_bar.id”, anonymous aliasing will be applied to one of the dupes. This allows the ORM to handle both columns independently; previously, 0.7 would in some cases silently emit a second SELECT for the column that was “duped”, and in 0.8 an ambiguous column error would be emitted. The “keys” applied to the .c. collection of the select() will also be deduped, so that the “column being replaced” warning will no longer emit for any select() that specifies use_labels, though the dupe key will be given an anonymous label which isn’t generally user-friendly.

  References: #2702

- [sql] [bug]

  Fixed bug where disconnect detect on error would raise an attribute error if the error were being raised after the Connection object had already been closed.

  References: #2691

- [sql] [bug]

  Reworked internal exception raises that emit a rollback() before re-raising, so that the stack trace is preserved from sys.exc_info() before entering the rollback. This so that the traceback is preserved when using coroutine frameworks which may have switched contexts before the rollback function returns.

  References: #2703

- [sql] [bug] [postgresql]

  The _Binary base type now converts values through the bytes() callable when run on Python 3; in particular psycopg2 2.5 with Python 3.3 seems to now be returning the “memoryview” type, so this is converted to bytes before return.

- [sql] [bug]

  Improvements to Connection auto-invalidation handling. If a non-disconnect error occurs, but leads to a delayed disconnect error within error handling (happens with MySQL), the disconnect condition is detected. The Connection can now also be closed when in an invalid state, meaning it will raise “closed” on next usage, and additionally the “close with result” feature will work even if the autorollback in an error handling routine fails and regardless of whether the condition is a disconnect or not.

  References: #2695

- [sql] [bug]

  Fixed bug whereby a DBAPI that can return “0” for cursor.lastrowid would not function correctly in conjunction with `ResultProxy.inserted_primary_key`.

### postgresql

- [postgresql] [bug]

  Opened up the checking for “disconnect” with psycopg2/libpq to check for all the various “disconnect” messages within the full exception hierarchy. Specifically the “closed the connection unexpectedly” message has now been seen in at least three different exception types. Courtesy Eli Collins.

  References: #2712

- [postgresql] [bug]

  The operators for the PostgreSQL ARRAY type supports input types of sets, generators, etc. even when a dimension is not specified, by turning the given iterable into a collection unconditionally.

  References: #2681

- [postgresql] [bug]

  Added missing HSTORE type to postgresql type names so that the type can be reflected.

  References: #2680

### mysql

- [mysql] [bug]

  Fixes to support the latest cymysql DBAPI, courtesy Hajime Nakagami.

- [mysql] [bug]

  Improvements to the operation of the pymysql dialect on Python 3, including some important decode/bytes steps. Issues remain with BLOB types due to driver issues. Courtesy Ben Trofatter.

  References: #2663

- [mysql] [bug]

  Updated a regexp to correctly extract error code on google app engine v1.7.5 and newer. Courtesy Dan Ring.

### mssql

- [mssql] [bug]

  Part of a longer series of fixes needed for pyodbc+ mssql, a CAST to NVARCHAR(max) has been added to the bound parameter for the table name and schema name in all information schema queries to avoid the issue of comparing NVARCHAR to NTEXT, which seems to be rejected by the ODBC driver in some cases, such as FreeTDS (0.91 only?) plus unicode bound parameters being passed. The issue seems to be specific to the SQL Server information schema tables and the workaround is harmless for those cases where the problem doesn’t exist in the first place.

  References: #2355

- [mssql] [bug]

  Added support for additional “disconnect” messages to the pymssql dialect. Courtesy John Anderson.

- [mssql] [bug]

  Fixed Py3K bug regarding “binary” types and pymssql. Courtesy Marc Abramowitz.

  References: #2683

## 0.8.0

Released: March 9, 2013

Note

There are some new behavioral changes as of 0.8.0 not present in 0.8.0b2. They are present in the migration document as follows:

- The consideration of a “pending” object as an “orphan” has been made more aggressive

- create_all() and drop_all() will now honor an empty list as such

- Correlation is now always context-specific

### orm

- [orm] [feature]

  A meaningful `QueryableAttribute.info` attribute is added, which proxies down to the `.info` attribute on either the `Column` object if directly present, or the `MapperProperty` otherwise. The full behavior is documented and ensured by tests to remain stable.

  References: #2675

- [orm] [feature]

  Can set/change the “cascade” attribute on a `relationship()` construct after it’s been constructed already. This is not a pattern for normal use but we like to change the setting for demonstration purposes in tutorials.

- [orm] [feature]

  Added new helper function `was_deleted()`, returns True if the given object was the subject of a `Session.delete()` operation.

  References: #2658

- [orm] [feature]

  Extended the Runtime Inspection API system so that all Python descriptors associated with the ORM or its extensions can be retrieved. This fulfills the common request of being able to inspect all `QueryableAttribute` descriptors in addition to extension types such as `hybrid_property` and `AssociationProxy`. See `Mapper.all_orm_descriptors`.

- [orm] [bug]

  Improved checking for an existing backref name conflict during mapper configuration; will now test for name conflicts on superclasses and subclasses, in addition to the current mapper, as these conflicts break things just as much. This is new for 0.8, but see below for a warning that will also be triggered in 0.7.11.

  References: #2674

- [orm] [bug]

  Improved the error message emitted when a “backref loop” is detected, that is when an attribute event triggers a bidirectional assignment between two other attributes with no end. This condition can occur not just when an object of the wrong type is assigned, but also when an attribute is mis-configured to backref into an existing backref pair. Also in 0.7.11.

  References: #2674

- [orm] [bug]

  A warning is emitted when a MapperProperty is assigned to a mapper that replaces an existing property, if the properties in question aren’t plain column-based properties. Replacement of relationship properties is rarely (ever?) what is intended and usually refers to a mapper mis-configuration. Also in 0.7.11.

  References: #2674

- [orm] [bug]

  A clear error message is emitted if an event handler attempts to emit SQL on a Session within the after_commit() handler, where there is not a viable transaction in progress.

  References: #2662

- [orm] [bug]

  Detection of a primary key change within the process of cascading a natural primary key update will succeed even if the key is composite and only some of the attributes have changed.

  References: #2665

- [orm] [bug]

  An object that’s deleted from a session will be de-associated with that session fully after the transaction is committed, that is the `object_session()` function will return None.

  References: #2658

- [orm] [bug]

  Fixed bug whereby `Query.yield_per()` would set the execution options incorrectly, thereby breaking subsequent usage of the `Query.execution_options()` method. Courtesy Ryan Kelly.

  References: #2661

- [orm] [bug]

  Fixed the consideration of the `between()` operator so that it works correctly with the new relationship local/remote system.

  References: #1768

- [orm] [bug]

  the consideration of a pending object as an “orphan” has been modified to more closely match the behavior as that of persistent objects, which is that the object is expunged from the `Session` as soon as it is de-associated from any of its orphan-enabled parents. Previously, the pending object would be expunged only if de-associated from all of its orphan-enabled parents. The new flag `legacy_is_orphan` is added to `Mapper` which re-establishes the legacy behavior.

  See the change note and example case at The consideration of a “pending” object as an “orphan” has been made more aggressive for a detailed discussion of this change.

  References: #2655

- [orm] [bug]

  Fixed the (most likely never used) “@collection.link” collection method, which fires off each time the collection is associated or de-associated with a mapped object - the decorator was not tested or functional. The decorator method is now named `collection.linker()` though the name “link” remains for backwards compatibility. Courtesy Luca Wehrstedt.

  References: #2653

- [orm] [bug]

  Made some fixes to the system of producing custom instrumented collections, mainly that the usage of the @collection decorators will now honor the __mro__ of the given class, applying the logic of the sub-most classes’ version of a particular collection method. Previously, it wasn’t predictable when subclassing an existing instrumented class such as `MappedCollection` whether or not custom methods would resolve correctly.

  References: #2654

- [orm] [bug]

  Fixed potential memory leak which could occur if an arbitrary number of `sessionmaker` objects were created. The anonymous subclass created by the sessionmaker, when dereferenced, would not be garbage collected due to remaining class-level references from the event package. This issue also applies to any custom system that made use of ad-hoc subclasses in conjunction with an event dispatcher. Also in 0.7.10.

  References: #2650

- [orm] [bug]

  `Query.merge_result()` can now load rows from an outer join where an entity may be `None` without throwing an error. Also in 0.7.10.

  References: #2640

- [orm] [bug]

  Fixes to the “dynamic” loader on `relationship()`, includes that backrefs will work properly even when autoflush is disabled, history events are more accurate in scenarios where multiple add/remove of the same object occurs.

  References: #2637

- [orm] [removed]

  The undocumented (and hopefully unused) system of producing custom collections using an `__instrumentation__` datastructure associated with the collection has been removed, as this was a complex and untested feature which was also essentially redundant versus the decorator approach. Other internal simplifications to the orm.collections module have been made as well.

### examples

- [examples] [bug]

  Fixed a regression in the examples/dogpile_caching example which was due to the change in #2614.

### sql

- [sql] [feature]

  Added a new argument to `Enum` and its base `SchemaType` `inherit_schema`. When set to `True`, the type will set its `schema` attribute of that of the `Table` to which it is associated. This also occurs during a `Table.tometadata()` operation; the `SchemaType` is now copied in all cases when `Table.tometadata()` happens, and if `inherit_schema=True`, the type will take on the new schema name passed to the method. The `schema` is important when used with the PostgreSQL backend, as the type results in a `CREATE TYPE` statement.

  References: #2657

- [sql] [feature]

  `Index` now supports arbitrary SQL expressions and/or functions, in addition to straight columns. Common modifiers include using `somecolumn.desc()` for a descending index and `func.lower(somecolumn)` for a case-insensitive index, depending on the capabilities of the target backend.

  References: #695

- [sql] [bug]

  The behavior of SELECT correlation has been improved such that the `Select.correlate()` and `Select.correlate_except()` methods, as well as their ORM analogues, will still retain “auto-correlation” behavior in that the FROM clause is modified only if the output would be legal SQL; that is, the FROM clause is left intact if the correlated SELECT is not used in the context of an enclosing SELECT inside of the WHERE, columns, or HAVING clause. The two methods now only specify conditions to the default “auto correlation”, rather than absolute FROM lists.

  References: #2668

- [sql] [bug]

  Fixed a bug regarding column annotations which in particular could impact some usages of the new `remote()` and `local()` annotation functions, where annotations could be lost when the column were used in a subsequent expression.

  References: #1768, #2660

- [sql] [bug]

  The `ColumnOperators.in_()` operator will now coerce values of `None` to `null()`.

  References: #2496

- [sql] [bug]

  Fixed bug where `Table.tometadata()` would fail if a `Column` had both a foreign key as well as an alternate “.key” name for the column. Also in 0.7.10.

  References: #2643

- [sql] [bug]

  insert().returning() raises an informative CompileError if attempted to compile on a dialect that doesn’t support RETURNING.

  References: #2629

- [sql] [bug]

  Tweaked the “REQUIRED” symbol used by the compiler to identify INSERT/UPDATE bound parameters that need to be passed, so that it’s more easily identifiable when writing custom bind-handling code.

  References: #2648

### schema

- [schema] [bug]

  `MetaData.create_all()` and `MetaData.drop_all()` will now accommodate an empty list as an instruction to not create/drop any items, rather than ignoring the collection.

  References: #2664

### postgresql

- [postgresql] [feature]

  Added support for PostgreSQL’s traditional SUBSTRING function syntax, renders as “SUBSTRING(x FROM y FOR z)” when regular `func.substring()` is used. Courtesy Gunnlaugur Þór Briem.

  This change is also backported to: 0.7.11

  References: #2676

- [postgresql] [feature]

  Added `Comparator.any()` and `Comparator.all()` methods, as well as standalone expression constructs. Big thanks to Audrius Kažukauskas for the terrific work here.

- [postgresql] [bug]

  Fixed bug in `array()` construct whereby using it inside of an `insert()` construct would produce an error regarding a parameter issue in the `self_group()` method.

### mysql

- [mysql] [feature]

  New dialect for CyMySQL added, courtesy Hajime Nakagami.

- [mysql] [feature]

  GAE dialect now accepts username/password arguments in the URL, courtesy Owen Nelson.

- [mysql] [bug] [gae]

  Added a conditional import to the `gaerdbms` dialect which attempts to import rdbms_apiproxy vs. rdbms_googleapi to work on both dev and production platforms. Also now honors the `instance` attribute. Courtesy Sean Lynch. Also in 0.7.10.

  References: #2649

- [mysql] [bug]

  GAE dialect won’t fail on None match if the error code can’t be extracted from the exception throw; courtesy Owen Nelson.

### mssql

- [mssql] [feature]

  Added `mssql_include` and `mssql_clustered` options to `Index`, renders the `INCLUDE` and `CLUSTERED` keywords, respectively. Courtesy Derek Harland.

- [mssql] [feature]

  DDL for IDENTITY columns is now supported on non-primary key columns, by establishing a `Sequence` construct on any integer column. Courtesy Derek Harland.

  References: #2644

- [mssql] [bug]

  Added a py3K conditional around unnecessary .decode() call in mssql information schema, fixes reflection in Py3K. Also in 0.7.10.

  References: #2638

- [mssql] [bug]

  Fixed a regression whereby the “collation” parameter of the character types CHAR, NCHAR, etc. stopped working, as “collation” is now supported by the base string types. The TEXT, NCHAR, CHAR, VARCHAR types within the MSSQL dialect are now synonyms for the base types.

### oracle

- [oracle] [bug]

  The cx_oracle dialect will no longer run the bind parameter names through `encode()`, as this is not valid on Python 3, and prevented statements from functioning correctly on Python 3. We now encode only if `supports_unicode_binds` is False, which is not the case for cx_oracle when at least version 5 of cx_oracle is used.

### tests

- [tests] [bug]

  Fixed an import of “logging” in test_execute which was not working on some linux platforms. Also in 0.7.11.

  References: #2669

## 0.8.0b2

Released: December 14, 2012

### orm

- [orm] [feature]

  Added `KeyedTuple._asdict()` and `KeyedTuple._fields` to the `KeyedTuple` class to provide some degree of compatibility with the Python standard library `collections.namedtuple()`.

  References: #2601

- [orm] [feature]

  Allow synonyms to be used when defining primary and secondary joins for relationships.

- [orm] [bug]

  The `Query.select_from()` method can now be used with a `aliased()` construct without it interfering with the entities being selected. Basically, a statement like this:

      ua = aliased(User)
      session.query(User.name).select_from(ua).join(User, User.name > ua.name)

  Will maintain the columns clause of the SELECT as coming from the unaliased “user”, as specified; the select_from only takes place in the FROM clause:

      SELECT users.name AS users_name FROM users AS users_1
      JOIN users ON users.name < users_1.name

  Note that this behavior is in contrast to the original, older use case for `Query.select_from()`, which is that of restating the mapped entity in terms of a different selectable:

      session.query(User.name).select_from(user_table.select().where(user_table.c.id > 5))

  Which produces:

      SELECT anon_1.name AS anon_1_name FROM (SELECT users.id AS id,
      users.name AS name FROM users WHERE users.id > :id_1) AS anon_1

  It was the “aliasing” behavior of the latter use case that was getting in the way of the former use case. The method now specifically considers a SQL expression like `select()` or `alias()` separately from a mapped entity like a `aliased()` construct.

  References: #2635

- [orm] [bug]

  The `MutableComposite` type did not allow for the `MutableBase.coerce()` method to be used, even though the code seemed to indicate this intent, so this now works and a brief example is added. As a side-effect, the mechanics of this event handler have been changed so that new `MutableComposite` types no longer add per-type global event handlers. Also in 0.7.10.

  References: #2624

- [orm] [bug]

  A second overhaul of aliasing/internal pathing mechanics now allows two subclasses to have different relationships of the same name, supported with subquery or joined eager loading on both simultaneously when a full polymorphic load is used.

  References: #2614

- [orm] [bug]

  Fixed bug whereby a multi-hop subqueryload within a particular with_polymorphic load would produce a KeyError. Takes advantage of the same internal pathing overhaul as #2614.

  References: #2617

- [orm] [bug]

  Fixed regression where query.update() would produce an error if an object matched by the “fetch” synchronization strategy wasn’t locally present. Courtesy Scott Torborg.

  References: #2602

### orm extensions

- [orm] [extensions] [feature]

  The `sqlalchemy.ext.mutable` extension now includes the example `MutableDict` class as part of the extension.

### engine

- [engine] [feature]

  The `Connection.connect()` and `Connection.contextual_connect()` methods now return a “branched” version so that the `Connection.close()` method can be called on the returned connection without affecting the original. Allows symmetry when using `Engine` and `Connection` objects as context managers:

      with conn.connect() as c:  # leaves the Connection open
          c.execute("...")

      with engine.connect() as c:  # closes the Connection
          c.execute("...")

- [engine] [bug]

  Fixed `MetaData.reflect()` to correctly use the given `Connection`, if given, without opening a second connection from that connection’s `Engine`.

  This change is also backported to: 0.7.10

  References: #2604

- [engine]

  The “reflect=True” argument to `MetaData` is deprecated. Please use the `MetaData.reflect()` method.

### sql

- [sql] [feature]

  The `Insert` construct now supports multi-valued inserts, that is, an INSERT that renders like “INSERT INTO table VALUES (…), (…), …”. Supported by PostgreSQL, SQLite, and MySQL. Big thanks to Idan Kamara for doing the legwork on this one.

  See also

  Multiple-VALUES support for Insert

  References: #2623

- [sql] [bug]

  Fixed bug where using server_onupdate=<FetchedValue|DefaultClause> without passing the “for_update=True” flag would apply the default object to the server_default, blowing away whatever was there. The explicit for_update=True argument shouldn’t be needed with this usage (especially since the documentation shows an example without it being used) so it is now arranged internally using a copy of the given default object, if the flag isn’t set to what corresponds to that argument.

  This change is also backported to: 0.7.10

  References: #2631

- [sql] [bug]

  Fixed a regression caused by #2410 whereby a `CheckConstraint` would apply itself back to the original table during a `Table.tometadata()` operation, as it would parse the SQL expression for a parent table. The operation now copies the given expression to correspond to the new table.

  References: #2633

- [sql] [bug]

  Fixed bug whereby using a label_length on dialect that was smaller than the size of actual column identifiers would fail to render the columns correctly in a SELECT statement.

  References: #2610

- [sql] [bug]

  The `DECIMAL` type now honors the “precision” and “scale” arguments when rendering DDL.

  References: #2618

- [sql] [bug]

  Made an adjustment to the “boolean”, (i.e. `__nonzero__`) evaluation of binary expressions, i.e. `x1 == x2`, such that the “auto-grouping” applied by `BinaryExpression` in some cases won’t get in the way of this comparison. Previously, an expression like:

      expr1 = mycolumn > 2
      bool(expr1 == expr1)

  Would evaluate as `False`, even though this is an identity comparison, because `mycolumn > 2` would be “grouped” before being placed into the `BinaryExpression`, thus changing its identity. `BinaryExpression` now keeps track of the “original” objects passed in. Additionally the `__nonzero__` method now only returns if the operator is `==` or `!=` - all others raise `TypeError`.

  References: #2621

- [sql] [bug]

  Fixed a gotcha where inadvertently calling list() on a `ColumnElement` would go into an endless loop, if `ColumnOperators.__getitem__()` were implemented. A new NotImplementedError is emitted via `__iter__()`.

- [sql] [bug]

  Fixed bug in type_coerce() whereby typing information could be lost if the statement were used as a subquery inside of another statement, as well as other similar situations. Among other things, would cause typing information to be lost when the Oracle/mssql dialects would apply limit/offset wrappings.

  References: #2603

- [sql] [bug]

  Fixed bug whereby the “.key” of a Column wasn’t being used when producing a “proxy” of the column against a selectable. This probably didn’t occur in 0.7 since 0.7 doesn’t respect the “.key” in a wider range of scenarios.

  References: #2597

### postgresql

- [postgresql] [feature]

  `HSTORE` is now available in the PostgreSQL dialect. Will also use psycopg2’s extensions if available. Courtesy Audrius Kažukauskas.

  References: #2606

### sqlite

- [sqlite] [bug]

  More adjustment to this SQLite related issue which was released in 0.7.9, to intercept legacy SQLite quoting characters when reflecting foreign keys. In addition to intercepting double quotes, other quoting characters such as brackets, backticks, and single quotes are now also intercepted.

  This change is also backported to: 0.7.10

  References: #2568

### mssql

- [mssql] [feature]

  Support for reflection of the “name” of primary key constraints added, courtesy Dave Moore.

  References: #2600

- [mssql] [bug]

  Fixed bug whereby using “key” with Column in conjunction with “schema” for the owning Table would fail to locate result rows due to the MSSQL dialect’s “schema rendering” logic’s failure to take .key into account.

  This change is also backported to: 0.7.10

### oracle

- [oracle] [bug]

  Fixed table reflection for Oracle when accessing a synonym that refers to a DBLINK remote database; while the syntax has been present in the Oracle dialect for some time, up until now it has never been tested. The syntax has been tested against a sample database linking to itself, however there’s still some uncertainty as to what should be used for the “owner” when querying the remote database for table information. Currently, the value of “username” from user_db_links is used to match the “owner”.

  References: #2619

- [oracle] [bug]

  The Oracle LONG type, while an unbounded text type, does not appear to use the cx_Oracle.LOB type when result rows are returned, so the dialect has been repaired to exclude LONG from having cx_Oracle.LOB filtering applied. Also in 0.7.10.

  References: #2620

- [oracle] [bug]

  Repaired the usage of `.prepare()` in conjunction with cx_Oracle so that a return value of `False` will result in no call to `connection.commit()`, hence avoiding “no transaction” errors. Two-phase transactions have now been shown to work in a rudimental fashion with SQLAlchemy and cx_oracle, however are subject to caveats observed with the driver; check the documentation for details. Also in 0.7.10.

  References: #2611

### misc

- [feature] [sybase]

  Reflection support has been added to the Sybase dialect. Big thanks to Ben Trofatter for all the work developing and testing this.

  References: #1753

- [feature] [pool]

  The `Pool` will now log all connection.close() operations equally, including closes which occur for invalidated connections, detached connections, and connections beyond the pool capacity.

- [feature] [pool]

  The `Pool` now consults the `Dialect` for functionality regarding how the connection should be “auto rolled back”, as well as closed. This grants more control of transaction scope to the dialect, so that we will be better able to implement transactional workarounds like those potentially needed for pysqlite and cx_oracle.

  References: #2611

- [feature] [pool]

  Added new `PoolEvents.reset()` hook to capture the event before a connection is auto-rolled back, upon return to the pool. Together with `ConnectionEvents.rollback()` this allows all rollback events to be intercepted.

- [bug] [firebird]

  Added missing import for “fdb” to the experimental “firebird+fdb” dialect.

  References: #2622

- [informix]

  Some cruft regarding informix transaction handling has been removed, including a feature that would skip calling commit()/rollback() as well as some hardcoded isolation level assumptions on begin().. The status of this dialect is not well understood as we don’t have any users working with it, nor any access to an Informix database. If someone with access to Informix wants to help test this dialect, please let us know.

## 0.8.0b1

Released: October 30, 2012

### general

- [general] [removed]

  The “sqlalchemy.exceptions” synonym for “sqlalchemy.exc” is removed fully.

  References: #2433

- [general]

  SQLAlchemy 0.8 now targets Python 2.5 and above. Python 2.4 is no longer supported.

### orm

- [orm] [feature]

  Major rewrite of relationship() internals now allow join conditions which include columns pointing to themselves within composite foreign keys. A new API for very specialized primaryjoin conditions is added, allowing conditions based on SQL functions, CAST, etc. to be handled by placing the annotation functions remote() and foreign() inline within the expression when necessary. Previous recipes using the semi-private _local_remote_pairs approach can be upgraded to this new approach.

  See also

  Rewritten _orm.relationship() mechanics

  References: #1401

- [orm] [feature]

  New standalone function with_polymorphic() provides the functionality of query.with_polymorphic() in a standalone form. It can be applied to any entity within a query, including as the target of a join in place of the “of_type()” modifier.

  References: #2333

- [orm] [feature]

  The of_type() construct on attributes now accepts aliased() class constructs as well as with_polymorphic constructs, and works with query.join(), any(), has(), and also eager loaders subqueryload(), joinedload(), contains_eager()

  References: #1106, #2438

- [orm] [feature]

  Improvements to event listening for mapped classes allows that unmapped classes can be specified for instance- and mapper-events. The established events will be automatically set up on subclasses of that class when the propagate=True flag is passed, and the events will be set up for that class itself if and when it is ultimately mapped.

  References: #2585

- [orm] [feature]

  The “deferred declarative reflection” system has been moved into the declarative extension itself, using the new DeferredReflection class. This class is now tested with both single and joined table inheritance use cases.

  References: #2485

- [orm] [feature]

  Added new core function “inspect()”, which serves as a generic gateway to introspection into mappers, objects, others. The Mapper and InstanceState objects have been enhanced with a public API that allows inspection of mapped attributes, including filters for column-bound or relationship-bound properties, inspection of current object state, history of attributes, etc.

  References: #2208

- [orm] [feature]

  Calling rollback() within a session.begin_nested() will now only expire those objects that had net changes within the scope of that transaction, that is objects which were dirty or were modified on a flush. This allows the typical use case for begin_nested(), that of altering a small subset of objects, to leave in place the data from the larger enclosing set of objects that weren’t modified in that sub-transaction.

  References: #2452

- [orm] [feature]

  Added utility feature Session.enable_relationship_loading(), supersedes relationship.load_on_pending. Both features should be avoided, however.

  References: #2372

- [orm] [feature]

  Added support for .info dictionary argument to column_property(), relationship(), composite(). All MapperProperty classes have an auto-creating .info dict available overall.

- [orm] [feature]

  Adding/removing None from a mapped collection now generates attribute events. Previously, a None append would be ignored in some cases. Related to.

  References: #2229

- [orm] [feature]

  The presence of None in a mapped collection now raises an error during flush. Previously, None values in collections would be silently ignored.

  References: #2229

- [orm] [feature]

  The Query.update() method is now more lenient as to the table being updated. Plain Table objects are better supported now, and additional a joined-inheritance subclass may be used with update(); the subclass table will be the target of the update, and if the parent table is referenced in the WHERE clause, the compiler will call upon UPDATE..FROM syntax as allowed by the dialect to satisfy the WHERE clause. MySQL’s multi-table update feature is also supported if columns are specified by object in the “values” dictionary. PG’s DELETE..USING is also not available in Core yet.

- [orm] [feature]

  New session events after_transaction_create and after_transaction_end allows tracking of new SessionTransaction objects. If the object is inspected, can be used to determine when a session first becomes active and when it deactivates.

- [orm] [feature]

  The Query can now load entity/scalar-mixed “tuple” rows that contain types which aren’t hashable, by setting the flag “hashable=False” on the corresponding TypeEngine object in use. Custom types that return unhashable types (typically lists) can set this flag to False.

  References: #2592

- [orm] [feature]

  Query now “auto correlates” by default in the same way as select() does. Previously, a Query used as a subquery in another would require the correlate() method be called explicitly in order to correlate a table on the inside to the outside. As always, correlate(None) disables correlation.

  References: #2179

- [orm] [feature]

  The after_attach event is now emitted after the object is established in Session.new or Session.identity_map upon Session.add(), Session.merge(), etc., so that the object is represented in these collections when the event is called. Added before_attach event to accommodate use cases that need autoflush w pre-attached object.

  References: #2464

- [orm] [feature]

  The Session will produce warnings when unsupported methods are used inside the “execute” portion of the flush. These are the familiar methods add(), delete(), etc. as well as collection and related-object manipulations, as called within mapper-level flush events like after_insert(), after_update(), etc. It’s been prominently documented for a long time that SQLAlchemy cannot guarantee results when the Session is manipulated within the execution of the flush plan, however users are still doing it, so now there’s a warning. Maybe someday the Session will be enhanced to support these operations inside of the flush, but for now, results can’t be guaranteed.

- [orm] [feature]

  ORM entities can be passed to the core select() construct as well as to the select_from(), correlate(), and correlate_except() methods of select(), where they will be unwrapped into selectables.

  References: #2245

- [orm] [feature]

  Some support for auto-rendering of a relationship join condition based on the mapped attribute, with usage of core SQL constructs. E.g. select([SomeClass]).where(SomeClass.somerelationship) would render SELECT from “someclass” and use the primaryjoin of “somerelationship” as the WHERE clause. This changes the previous meaning of “SomeClass.somerelationship” when used in a core SQL context; previously, it would “resolve” to the parent selectable, which wasn’t generally useful. Also works with query.filter(). Related to.

  References: #2245

- [orm] [feature]

  The registry of classes in declarative_base() is now a WeakValueDictionary. So subclasses of “Base” that are dereferenced will be garbage collected, if they are not referred to by any other mappers/superclass mappers. See the next note for this ticket.

  References: #2526

- [orm] [feature]

  Conflicts between columns on single-inheritance declarative subclasses, with or without using a mixin, can be resolved using a new @declared_attr usage described in the documentation.

  References: #2472

- [orm] [feature]

  declared_attr can now be used on non-mixin classes, even though this is generally only useful for single-inheritance subclass column conflict resolution.

  References: #2472

- [orm] [feature]

  declared_attr can now be used with attributes that are not Column or MapperProperty; including any user-defined value as well as association proxy objects.

  References: #2517

- [orm] [feature]

  Very limited support for inheriting mappers to be GC’ed when the class itself is deferenced. The mapper must not have its own table (i.e. single table inh only) without polymorphic attributes in place. This allows for the use case of creating a temporary subclass of a declarative mapped class, with no table or mapping directives of its own, to be garbage collected when dereferenced by a unit test.

  References: #2526

- [orm] [feature]

  Declarative now maintains a registry of classes by string name as well as by full module-qualified name. Multiple classes with the same name can now be looked up based on a module-qualified string within relationship(). Simple class name lookups where more than one class shares the same name now raises an informative error message.

  References: #2338

- [orm] [feature]

  Can now provide class-bound attributes that override columns which are of any non-ORM type, not just descriptors.

  References: #2535

- [orm] [feature]

  Added with_labels and reduce_columns keyword arguments to Query.subquery(), to provide two alternate strategies for producing queries with uniquely- named columns. .

  References: #1729

- [orm] [feature]

  A warning is emitted when a reference to an instrumented collection is no longer associated with the parent class due to expiration/attribute refresh/collection replacement, but an append or remove operation is received on the now-detached collection.

  References: #2476

- [orm] [bug]

  ORM will perform extra effort to determine that an FK dependency between two tables is not significant during flush if the tables are related via joined inheritance and the FK dependency is not part of the inherit_condition, saves the user a use_alter directive.

  References: #2527

- [orm] [bug]

  The instrumentation events class_instrument(), class_uninstrument(), and attribute_instrument() will now fire off only for descendant classes of the class assigned to listen(). Previously, an event listener would be assigned to listen for all classes in all cases regardless of the “target” argument passed.

  References: #2590

- [orm] [bug]

  with_polymorphic() produces JOINs in the correct order and with correct inheriting tables in the case of sending multi-level subclasses in an arbitrary order or with intermediary classes missing.

  References: #1900

- [orm] [bug]

  Improvements to joined/subquery eager loading dealing with chains of subclass entities sharing a common base, with no specific “join depth” provided. Will chain out to each subclass mapper individually before detecting a “cycle”, rather than considering the base class to be the source of the “cycle”.

  References: #2481

- [orm] [bug]

  The “passive” flag on Session.is_modified() no longer has any effect. is_modified() in all cases looks only at local in-memory modified flags and will not emit any SQL or invoke loader callables/initializers.

  References: #2320

- [orm] [bug]

  The warning emitted when using delete-orphan cascade with one-to-many or many-to-many without single-parent=True is now an error. The ORM would fail to function subsequent to this warning in any case.

  References: #2405

- [orm] [bug]

  Lazy loads emitted within flush events such as before_flush(), before_update(), etc. will now function as they would within non-event code, regarding consideration of the PK/FK values used in the lazy-emitted query. Previously, special flags would be established that would cause lazy loads to load related items based on the “previous” value of the parent PK/FK values specifically when called upon within a flush; the signal to load in this way is now localized to where the unit of work actually needs to load that way. Note that the UOW does sometimes load these collections before the before_update() event is called, so the usage of “passive_updates” or not can affect whether or not a collection will represent the “old” or “new” data, when accessed within a flush event, based on when the lazy load was emitted. The change is backwards incompatible in the exceedingly small chance that user event code depended on the old behavior.

  References: #2350

- [orm] [bug]

  Continuing regarding extra state post-flush due to event listeners; any states that are marked as “dirty” from an attribute perspective, usually via column-attribute set events within after_insert(), after_update(), etc., will get the “history” flag reset in all cases, instead of only those instances that were part of the flush. This has the effect that this “dirty” state doesn’t carry over after the flush and won’t result in UPDATE statements. A warning is emitted to this effect; the set_committed_state() method can be used to assign attributes on objects without producing history events.

  References: #2566, #2582

- [orm] [bug]

  Fixed a disconnect that slowly evolved between a @declared_attr Column and a directly-defined Column on a mixin. In both cases, the Column will be applied to the declared class’ table, but not to that of a joined inheritance subclass. Previously, the directly-defined Column would be placed on both the base and the sub table, which isn’t typically what’s desired.

  References: #2565

- [orm] [bug]

  Declarative can now propagate a column declared on a single-table inheritance subclass up to the parent class’ table, when the parent class is itself mapped to a join() or select() statement, directly or via joined inheritance, and not just a Table.

  References: #2549

- [orm] [bug]

  An error is emitted when uselist=False is combined with a “dynamic” loader. This is a warning in 0.7.9.

- [orm] [removed]

  The legacy “mutable” system of the ORM, including the MutableType class as well as the mutable=True flag on PickleType and postgresql.ARRAY has been removed. In-place mutations are detected by the ORM using the sqlalchemy.ext.mutable extension, introduced in 0.7. The removal of MutableType and associated constructs removes a great deal of complexity from SQLAlchemy’s internals. The approach performed poorly as it would incur a scan of the full contents of the Session when in use.

  References: #2442

- [orm] [removed]

  Deprecated identifiers removed:

  - allow_null_pks mapper() argument (use allow_partial_pks)

  - _get_col_to_prop() mapper method (use get_property_by_column())

  - dont_load argument to Session.merge() (use load=True)

  - sqlalchemy.orm.shard module (use sqlalchemy.ext.horizontal_shard)

- [orm] [moved]

  The InstrumentationManager interface and the entire related system of alternate class implementation is now moved out to sqlalchemy.ext.instrumentation. This is a seldom used system that adds significant complexity and overhead to the mechanics of class instrumentation. The new architecture allows it to remain unused until InstrumentationManager is actually imported, at which point it is bootstrapped into the core.

### examples

- [examples]

  The Beaker caching example has been converted to use dogpile.cache. This is a new caching library written by the same creator of Beaker’s caching internals, and represents a vastly improved, simplified, and modernized system of caching.

  See also

  Dogpile Caching

  References: #2589

### engine

- [engine] [feature]

  Connection event listeners can now be associated with individual Connection objects, not just Engine objects.

  References: #2511

- [engine] [feature]

  The before_cursor_execute event fires off for so-called “_cursor_execute” events, which are usually special-case executions of primary-key bound sequences and default-generation SQL phrases that invoke separately when RETURNING is not used with INSERT.

  References: #2459

- [engine] [feature]

  The libraries used by the test suite have been moved around a bit so that they are part of the SQLAlchemy install again. In addition, a new suite of tests is present in the new sqlalchemy.testing.suite package. This is an under-development system that hopes to provide a universal testing suite for external dialects. Dialects which are maintained outside of SQLAlchemy can use the new test fixture as the framework for their own tests, and will get for free a “compliance” suite of dialect-focused tests, including an improved “requirements” system where specific capabilities and features can be enabled or disabled for testing.

- [engine] [feature]

  Added a new system for registration of new dialects in-process without using an entrypoint. See the docs for “Registering New Dialects”.

  References: #2462

- [engine] [feature]

  The “required” flag is set to True by default, if not passed explicitly, on bindparam() if the “value” or “callable” parameters are not passed. This will cause statement execution to check for the parameter being present in the final collection of bound parameters, rather than implicitly assigning None.

  References: #2556

- [engine] [feature]

  Various API tweaks to the “dialect” API to better support highly specialized systems such as the Akiban database, including more hooks to allow an execution context to access type processors.

- [engine] [feature]

  Inspector.get_primary_keys() is deprecated; use Inspector.get_pk_constraint(). Courtesy Diana Clarke.

  References: #2422

- [engine] [feature]

  New C extension module “utils” has been added for additional function speedups as we have time to implement.

- [engine] [bug]

  The Inspector.get_table_names() order_by=”foreign_key” feature now sorts tables by dependee first, to be consistent with util.sort_tables and metadata.sorted_tables.

- [engine] [bug]

  Fixed bug whereby if a database restart affected multiple connections, each connection would individually invoke a new disposal of the pool, even though only one disposal is needed.

  References: #2522

- [engine] [bug]

  The names of the columns on the .c. attribute of a select().apply_labels() is now based on <tablename>_<colkey> instead of <tablename>_<colname>, for those columns that have a distinctly named .key.

  References: #2397

- [engine] [bug]

  The autoload_replace flag on Table, when False, will cause any reflected foreign key constraints which refer to already-declared columns to be skipped, assuming that the in-Python declared column will take over the task of specifying in-Python ForeignKey or ForeignKeyConstraint declarations.

- [engine] [bug]

  The ResultProxy methods inserted_primary_key, last_updated_params(), last_inserted_params(), postfetch_cols(), prefetch_cols() all assert that the given statement is a compiled construct, and is an insert() or update() statement as is appropriate, else raise InvalidRequestError.

  References: #2498

- [engine]

  ResultProxy.last_inserted_ids is removed, replaced by inserted_primary_key.

### sql

- [sql] [feature]

  Added a new method `Engine.execution_options()` to `Engine`. This method works similarly to `Connection.execution_options()` in that it creates a copy of the parent object which will refer to the new set of options. The method can be used to build sharding schemes where each engine shares the same underlying pool of connections. The method has been tested against the horizontal shard recipe in the ORM as well.

  See also

  `Engine.execution_options()`

- [sql] [feature]

  Major rework of operator system in Core, to allow redefinition of existing operators as well as addition of new operators at the type level. New types can be created from existing ones which add or redefine operations that are exported out to column expressions, in a similar manner to how the ORM has allowed comparator_factory. The new architecture moves this capability into the Core so that it is consistently usable in all cases, propagating cleanly using existing type propagation behavior.

  References: #2547

- [sql] [feature]

  To complement, types can now provide “bind expressions” and “column expressions” which allow compile-time injection of SQL expressions into statements on a per-column or per-bind level. This is to suit the use case of a type which needs to augment bind- and result- behavior at the SQL level, as opposed to in the Python level. Allows for schemes like transparent encryption/ decryption, usage of PostGIS functions, etc.

  References: #1534, #2547

- [sql] [feature]

  The Core operator system now includes the getitem operator, i.e. the bracket operator in Python. This is used at first to provide index and slice behavior to the PostgreSQL ARRAY type, and also provides a hook for end-user definition of custom __getitem__ schemes which can be applied at the type level as well as within ORM-level custom operator schemes. lshift (<<) and rshift (>>) are also supported as optional operators.

  Note that this change has the effect that descriptor-based __getitem__ schemes used by the ORM in conjunction with synonym() or other “descriptor-wrapped” schemes will need to start using a custom comparator in order to maintain this behavior.

- [sql] [feature]

  Revised the rules used to determine the operator precedence for the user-defined operator, i.e. that granted using the `op()` method. Previously, the smallest precedence was applied in all cases, now the default precedence is zero, lower than all operators except “comma” (such as, used in the argument list of a `func` call) and “AS”, and is also customizable via the “precedence” argument on the `op()` method.

  References: #2537

- [sql] [feature]

  Added “collation” parameter to all String types. When present, renders as COLLATE <collation>. This to support the COLLATE keyword now supported by several databases including MySQL, SQLite, and PostgreSQL.

  References: #2276

- [sql] [feature]

  Custom unary operators can now be used by combining operators.custom_op() with UnaryExpression().

- [sql] [feature]

  Enhanced GenericFunction and func.* to allow for user-defined GenericFunction subclasses to be available via the func.* namespace automatically by classname, optionally using a package name, as well as with the ability to have the rendered name different from the identified name in func.*.

- [sql] [feature]

  The cast() and extract() constructs will now be produced via the func.* accessor as well, as users naturally try to access these names from func.* they might as well do what’s expected, even though the returned object is not a FunctionElement.

  References: #2562

- [sql] [feature]

  The Inspector object can now be acquired using the new inspect() service, part of

  References: #2208

- [sql] [feature]

  The column_reflect event now accepts the Inspector object as the first argument, preceding “table”. Code which uses the 0.7 version of this very new event will need modification to add the “inspector” object as the first argument.

  References: #2418

- [sql] [feature]

  The behavior of column targeting in result sets is now case sensitive by default. SQLAlchemy for many years would run a case-insensitive conversion on these values, probably to alleviate early case sensitivity issues with dialects like Oracle and Firebird. These issues have been more cleanly solved in more modern versions so the performance hit of calling lower() on identifiers is removed. The case insensitive comparisons can be re-enabled by setting “case_insensitive=False” on create_engine().

  References: #2423

- [sql] [feature]

  The “unconsumed column names” warning emitted when keys are present in insert.values() or update.values() that aren’t in the target table is now an exception.

  References: #2415

- [sql] [feature]

  Added “MATCH” clause to ForeignKey, ForeignKeyConstraint, courtesy Ryan Kelly.

  References: #2502

- [sql] [feature]

  Added support for DELETE and UPDATE from an alias of a table, which would assumedly be related to itself elsewhere in the query, courtesy Ryan Kelly.

  References: #2507

- [sql] [feature]

  select() features a correlate_except() method, auto correlates all selectables except those passed.

- [sql] [feature]

  The prefix_with() method is now available on each of select(), insert(), update(), delete(), all with the same API, accepting multiple prefix calls, as well as a “dialect name” so that the prefix can be limited to one kind of dialect.

  References: #2431

- [sql] [feature]

  Added reduce_columns() method to select() construct, replaces columns inline using the util.reduce_columns utility function to remove equivalent columns. reduce_columns() also adds “with_only_synonyms” to limit the reduction just to those columns which have the same name. The deprecated fold_equivalents() feature is removed.

  References: #1729

- [sql] [feature]

  Reworked the startswith(), endswith(), contains() operators to do a better job with negation (NOT LIKE), and also to assemble them at compilation time so that their rendered SQL can be altered, such as in the case for Firebird STARTING WITH

  References: #2470

- [sql] [feature]

  Added a hook to the system of rendering CREATE TABLE that provides access to the render for each Column individually, by constructing a @compiles function against the new schema.CreateColumn construct.

  References: #2463

- [sql] [feature]

  ”scalar” selects now have a WHERE method to help with generative building. Also slight adjustment regarding how SS “correlates” columns; the new methodology no longer applies meaning to the underlying Table column being selected. This improves some fairly esoteric situations, and the logic that was there didn’t seem to have any purpose.

- [sql] [feature]

  An explicit error is raised when a ForeignKeyConstraint() that was constructed to refer to multiple remote tables is first used.

  References: #2455

- [sql] [feature]

  Added `ColumnOperators.notin_()`, `ColumnOperators.notlike()`, `ColumnOperators.notilike()` to `ColumnOperators`.

  References: #2580

- [sql] [change]

  The Text() type renders the length given to it, if a length was specified.

- [sql] [changed]

  Most classes in expression.sql are no longer preceded with an underscore, i.e. Label, SelectBase, Generative, CompareMixin. _BindParamClause is also renamed to BindParameter. The old underscore names for these classes will remain available as synonyms for the foreseeable future.

- [sql] [bug]

  Fixed bug where keyword arguments passed to `Compiler.process()` wouldn’t get propagated to the column expressions present in the columns clause of a SELECT statement. In particular this would come up when used by custom compilation schemes that relied upon special flags.

  References: #2593

- [sql] [bug] [orm]

  The auto-correlation feature of `select()`, and by proxy that of `Query`, will not take effect for a SELECT statement that is being rendered directly in the FROM list of the enclosing SELECT. Correlation in SQL only applies to column expressions such as those in the WHERE, ORDER BY, columns clause.

  References: #2595

- [sql] [bug]

  A tweak to column precedence which moves the “concat” and “match” operators to be the same as that of “is”, “like”, and others; this helps with parenthesization rendering when used in conjunction with “IS”.

  References: #2564

- [sql] [bug]

  Applying a column expression to a select statement using a label with or without other modifying constructs will no longer “target” that expression to the underlying Column; this affects ORM operations that rely upon Column targeting in order to retrieve results. That is, a query like query(User.id, User.id.label(‘foo’)) will now track the value of each “User.id” expression separately instead of munging them together. It is not expected that any users will be impacted by this; however, a usage that uses select() in conjunction with query.from_statement() and attempts to load fully composed ORM entities may not function as expected if the select() named Column objects with arbitrary .label() names, as these will no longer target to the Column objects mapped by that entity.

  References: #2591

- [sql] [bug]

  Fixes to the interpretation of the Column “default” parameter as a callable to not pass ExecutionContext into a keyword argument parameter.

  References: #2520

- [sql] [bug]

  All of UniqueConstraint, ForeignKeyConstraint, CheckConstraint, and PrimaryKeyConstraint will attach themselves to their parent table automatically when they refer to a Table-bound Column object directly (i.e. not just string column name), and refer to one and only one Table. Prior to 0.8 this behavior occurred for UniqueConstraint and PrimaryKeyConstraint, but not ForeignKeyConstraint or CheckConstraint.

  References: #2410

- [sql] [bug]

  TypeDecorator now includes a generic repr() that works in terms of the “impl” type by default. This is a behavioral change for those TypeDecorator classes that specify a custom __init__ method; those types will need to re-define __repr__() if they need __repr__() to provide a faithful constructor representation.

  References: #2594

- [sql] [bug]

  column.label(None) now produces an anonymous label, instead of returning the column object itself, consistent with the behavior of label(column, None).

  References: #2168

- [sql] [removed]

  The long-deprecated and non-functional `assert_unicode` flag on `create_engine()` as well as `String` is removed.

### postgresql

- [postgresql] [feature]

  postgresql.ARRAY features an optional “dimension” argument, will assign a specific number of dimensions to the array which will render in DDL as ARRAY[][]…, also improves performance of bind/result processing.

  References: #2441

- [postgresql] [feature]

  postgresql.ARRAY now supports indexing and slicing. The Python [] operator is available on all SQL expressions that are of type ARRAY; integer or simple slices can be passed. The slices can also be used on the assignment side in the SET clause of an UPDATE statement by passing them into Update.values(); see the docs for examples.

- [postgresql] [feature]

  Added new “array literal” construct postgresql.array(). Basically a “tuple” that renders as ARRAY[1,2,3].

- [postgresql] [feature]

  Added support for the PostgreSQL ONLY keyword, which can appear corresponding to a table in a SELECT, UPDATE, or DELETE statement. The phrase is established using with_hint(). Courtesy Ryan Kelly

  References: #2506

- [postgresql] [feature]

  The “ischema_names” dictionary of the PostgreSQL dialect is “unofficially” customizable. Meaning, new types such as PostGIS types can be added into this dictionary, and the PG type reflection code should be able to handle simple types with variable numbers of arguments. The functionality here is “unofficial” for three reasons:

  1. this is not an “official” API. Ideally an “official” API would allow custom type-handling callables at the dialect or global level in a generic way.

  2. This is only implemented for the PG dialect, in particular because PG has broad support for custom types vs. other database backends. A real API would be implemented at the default dialect level.

  3. The reflection code here is only tested against simple types and probably has issues with more compositional types.

  patch courtesy Éric Lemoine.

### mysql

- [mysql] [feature]

  Added TIME type to mysql dialect, accepts “fst” argument which is the new “fractional seconds” specifier for recent MySQL versions. The datatype will interpret a microseconds portion received from the driver, however note that at this time most/all MySQL DBAPIs do not support returning this value.

  References: #2534

- [mysql] [bug]

  Dialect no longer emits expensive server collations query, as well as server casing, on first connect. These functions are still available as semi-private.

  References: #2404

### sqlite

- [sqlite] [feature]

  the SQLite date and time types have been overhauled to support a more open ended format for input and output, using name based format strings and regexps. A new argument “microseconds” also provides the option to omit the “microseconds” portion of timestamps. Thanks to Nathan Wright for the work and tests on this.

  References: #2363

- [sqlite]

  Added `NCHAR`, `NVARCHAR` to the SQLite dialect’s list of recognized type names for reflection. SQLite returns the name given to a type as the name returned.

  References: rc3addcc9ffad

### mssql

- [mssql] [feature]

  SQL Server dialect can be given database-qualified schema names, i.e. “schema=’mydatabase.dbo’”; reflection operations will detect this, split the schema among the “.” to get the owner separately, and emit a “USE mydatabase” statement before reflecting targets within the “dbo” owner; the existing database returned from DB_NAME() is then restored.

- [mssql] [feature]

  updated support for the mxodbc driver; mxodbc 3.2.1 is recommended for full compatibility.

- [mssql] [bug]

  removed legacy behavior whereby a column comparison to a scalar SELECT via == would coerce to an IN with the SQL server dialect. This is implicit behavior which fails in other scenarios so is removed. Code which relies on this needs to be modified to use column.in_(select) explicitly.

  References: #2277

### oracle

- [oracle] [feature]

  The types of columns excluded from the setinputsizes() set can be customized by sending a list of string DBAPI type names to exclude, using the exclude_setinputsizes dialect parameter. This list was previously fixed. The list also now defaults to STRING, UNICODE, removing CLOB, NCLOB from the list.

  References: #2561

- [oracle] [bug]

  Quoting information is now passed along from a Column with quote=True when generating a same-named bound parameter to the bindparam() object, as is the case in generated INSERT and UPDATE statements, so that unknown reserved names can be fully supported.

  References: #2437

- [oracle] [bug]

  The CreateIndex construct in Oracle will now schema-qualify the name of the index to be that of the parent table. Previously this name was omitted which apparently creates the index in the default schema, rather than that of the table.

### misc

- [feature] [access]

  the MS Access dialect has been moved to its own project on Bitbucket, taking advantage of the new SQLAlchemy dialect compliance suite. The dialect is still in very rough shape and probably not ready for general use yet, however it does have extremely rudimental functionality now. https://github.com/gordthompson/sqlalchemy-access

- [feature] [firebird]

  The “startswith()” operator renders as “STARTING WITH”, “~startswith()” renders as “NOT STARTING WITH”, using FB’s more efficient operator.

  References: #2470

- [feature] [firebird]

  An experimental dialect for the fdb driver is added, but is untested as I cannot get the fdb package to build.

  References: #2504

- [bug] [firebird]

  CompileError is raised when VARCHAR with no length is attempted to be emitted, same way as MySQL.

  References: #2505

- [bug] [firebird]

  Firebird now uses strict “ansi bind rules” so that bound parameters don’t render in the columns clause of a statement - they render literally instead.

- [bug] [firebird]

  Support for passing datetime as date when using the DateTime type with Firebird; other dialects support this.

- [moved] [maxdb]

  The MaxDB dialect, which hasn’t been functional for several years, is moved out to a pending bitbucket project, (deleted; to view the MaxDB code see the commit before it was removed at https://github.com/sqlalchemy/sqlalchemy/tree/ba67f7dbc5eb7a1ed2a3e1b56df72a837130f7bb/lib/sqlalchemy/dialects/maxdb)