operations.py 文件源码

def create_check_constraint(self, name, source, condition,
                                schema=None, **kw):
        """Issue a "create check constraint" instruction using the
        current migration context.

        e.g.::

            from alembic import op
            from sqlalchemy.sql import column, func

            op.create_check_constraint(
                "ck_user_name_len",
                "user",
                func.len(column('name')) > 5
            )

        CHECK constraints are usually against a SQL expression, so ad-hoc
        table metadata is usually needed.   The function will convert the given
        arguments into a :class:`sqlalchemy.schema.CheckConstraint` bound
        to an anonymous table in order to emit the CREATE statement.

        :param name: Name of the check constraint.  The name is necessary
         so that an ALTER statement can be emitted.  For setups that
         use an automated naming scheme such as that described at
         `NamingConventions <http://www.sqlalchemy.org/trac/wiki/UsageRecipes/NamingConventions>`_,
         ``name`` here can be ``None``, as the event listener will
         apply the name to the constraint object when it is associated
         with the table.
        :param source: String name of the source table.
        :param condition: SQL expression that's the condition of the constraint.
         Can be a string or SQLAlchemy expression language structure.
        :param deferrable: optional bool. If set, emit DEFERRABLE or NOT DEFERRABLE when
         issuing DDL for this constraint.
        :param initially: optional string. If set, emit INITIALLY <value> when issuing DDL
         for this constraint.
        :param schema: Optional schema name to operate within.

         ..versionadded:: 0.4.0

        """
        self.impl.add_constraint(
            self._check_constraint(name, source, condition, schema=schema, **kw)
        )