Toql is an SQL friendly ORM. Instead of mapping a struct field to a column you can also map it to a raw SQL expression. There are small syntax enhancements to work with aliases and auxiliary parameters.

# #![allow(unused_variables)]
#fn main() {
#[derive(Toql)]
struct User {
    #[toql(key)]
    id: u64,

    #[toql(sql="(SELECT COUNT(*) FROM Books b WHERE b.author_id = ..id)")]
    number_of_book:u64
}
#}

Notice the .. ! This special alias will be replaced with the alias crated for User. The generated SELECT might look like this:

SELECT t0.id, (SELECT COUNT(*) FROM Books WHERE author_id = t0.id) FROM User t0

To use aux params in a SQL query use the <param_name> syntax.

# #![allow(unused_variables)]
#fn main() {
#[derive(Toql)]
struct User {
    #[toql(key)]
    id: u64,

    #[toql(sql="(SELECT <page_limit>)")]
    page_limit:u64

     #[toql(sql="(SELECT COUNT(*) FROM Films f WHERE f.age >= <age>)")]
    age_rated_films:u64
}
#}

In the example page_limit might come from a server configuration. It would typically be put in the context and can be used in SQL expressions.

The aux param age might be taken from the authorisation token and put as an aux param into the context or query. Here it restricts the number of films.

There are other places you can use raw SQL:

• Predicates
• Custom Merge