sqlalchemy.sql.elements.TypeCoerce

Associate a SQL expression with a particular type, without rendering CAST.

E.g.:

from sqlalchemy import type_coerce

stmt = select(type_coerce(log_table.date_string, StringDateTime()))

The above construct will produce a .TypeCoerce object, which does not modify the rendering in any way on the SQL side, with the possible exception of a generated label if used in a columns clause context:

SELECT date_string AS date_string FROM log

When result rows are fetched, the StringDateTime type processor will be applied to result rows on behalf of the date_string column.

In order to provide a named label for the expression, use _expression.ColumnElement.label:

stmt = select(
    type_coerce(log_table.date_string, StringDateTime()).label('date')
)

A type that features bound-value handling will also have that behavior take effect when literal values or .bindparam constructs are passed to .type_coerce as targets. For example, if a type implements the .TypeEngine.bind_expression method or .TypeEngine.bind_processor method or equivalent, these functions will take effect at statement compilation/execution time when a literal value is passed, as in:

# bound-value handling of MyStringType will be applied to the
# literal value "some string"
stmt = select(type_coerce("some string", MyStringType))

When using .type_coerce with composed expressions, note that parenthesis are not applied. If .type_coerce is being used in an operator context where the parenthesis normally present from CAST are necessary, use the .TypeCoerce.self_group method:

>>> some_integer = column("someint", Integer)
>>> some_string = column("somestr", String)
>>> expr = type_coerce(some_integer + 5, String) + some_string
>>> print(expr)
someint + :someint_1 || somestr
>>> expr = type_coerce(some_integer + 5, String).self_group() + some_string
>>> print(expr)
(someint + :someint_1) || somestr

Apply a 'grouping' to this _expression.ClauseElement.

This method is overridden by subclasses to return a "grouping" construct, i.e. parenthesis. In particular it's used by "binary" expressions to provide a grouping around themselves when placed into a larger expression, as well as by _expression.select constructs when placed into the FROM clause of another _expression.select. (Note that subqueries should be normally created using the _expression.Select.alias method, as many platforms require nested SELECT statements to be named).

As expressions are composed together, the application of self_group is automatic - end-user code should never need to use this method directly. Note that SQLAlchemy's clause constructs take operator precedence into account - so parenthesis might not be needed, for example, in an expression like x OR (y AND z) - AND takes precedence over OR.

The base self_group method of _expression.ClauseElement just returns self.

Undocumented