Module « sqlalchemy »

Fonction type_coerce - module sqlalchemy

Signature de la fonction type_coerce

def type_coerce(expression, type_) 

Description

type_coerce.__doc__

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 :class:`.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.

        .. note:: the :func:`.type_coerce` construct does not render any
           SQL syntax of its own, including that it does not imply
           parenthesization.   Please use :meth:`.TypeCoerce.self_group`
           if explicit parenthesization is required.

        In order to provide a named label for the expression, use
        :meth:`_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 :func:`.bindparam` constructs are
        passed to :func:`.type_coerce` as targets.
        For example, if a type implements the
        :meth:`.TypeEngine.bind_expression`
        method or :meth:`.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 :func:`.type_coerce` with composed expressions, note that
        **parenthesis are not applied**.   If :func:`.type_coerce` is being
        used in an operator context where the parenthesis normally present from
        CAST are necessary, use the :meth:`.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

        :param expression: A SQL expression, such as a
         :class:`_expression.ColumnElement`
         expression or a Python string which will be coerced into a bound
         literal value.

        :param type\_: A :class:`.TypeEngine` class or instance indicating
         the type to which the expression is coerced.

        .. seealso::

            :ref:`coretutorial_casts`

            :func:`.cast`