operations.py 文件源码

def f(self, name):
        """Indicate a string name that has already had a naming convention
        applied to it.

        This feature combines with the SQLAlchemy ``naming_convention`` feature
        to disambiguate constraint names that have already had naming
        conventions applied to them, versus those that have not.  This is
        necessary in the case that the ``"%(constraint_name)s"`` token
        is used within a naming convention, so that it can be identified
        that this particular name should remain fixed.

        If the :meth:`.Operations.f` is used on a constraint, the naming
        convention will not take effect::

            op.add_column('t', 'x', Boolean(name=op.f('ck_bool_t_x')))

        Above, the CHECK constraint generated will have the name
        ``ck_bool_t_x`` regardless of whether or not a naming convention is
        in use.

        Alternatively, if a naming convention is in use, and 'f' is not used,
        names will be converted along conventions.  If the ``target_metadata``
        contains the naming convention
        ``{"ck": "ck_bool_%(table_name)s_%(constraint_name)s"}``, then the
        output of the following:

            op.add_column('t', 'x', Boolean(name='x'))

        will be::

            CONSTRAINT ck_bool_t_x CHECK (x in (1, 0)))

        The function is rendered in the output of autogenerate when
        a particular constraint name is already converted, for SQLAlchemy
        version **0.9.4 and greater only**.   Even though ``naming_convention``
        was introduced in 0.9.2, the string disambiguation service is new
        as of 0.9.4.

        .. versionadded:: 0.6.4

        """
        if conv:
            return conv(name)
        else:
            raise NotImplementedError(
                "op.f() feature requires SQLAlchemy 0.9.4 or greater.")