ops.py 文件源码

def create_check_constraint(
            cls, operations,
            constraint_name, table_name, 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
         :ref:`sqla:constraint_naming_conventions`,
         ``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 table_name: 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.  To control
         quoting of the schema outside of the default behavior, use
         the SQLAlchemy construct
         :class:`~sqlalchemy.sql.elements.quoted_name`.

         .. versionadded:: 0.7.0 'schema' can now accept a
            :class:`~sqlalchemy.sql.elements.quoted_name` construct.

        .. versionchanged:: 0.8.0 The following positional argument names
           have been changed:

           * name -> constraint_name
           * source -> table_name

        """
        op = cls(constraint_name, table_name, condition, schema=schema, **kw)
        return operations.invoke(op)