Method as_mutable

lib/sqlalchemy/ext/mutable.py:660–743

Associate a SQL type with this mutable Python type. This establishes listeners that will detect ORM mappings against the given type, adding mutation event trackers to those mappings. The type is returned, unconditionally as an instance, so that :meth:`.as_mutable` c

(cls, sqltype: _TypeEngineArgument[_T])

    @classmethod
    def as_mutable(cls, sqltype: _TypeEngineArgument[_T]) -> TypeEngine[_T]:
        """Associate a SQL type with this mutable Python type.

        This establishes listeners that will detect ORM mappings against
        the given type, adding mutation event trackers to those mappings.

        The type is returned, unconditionally as an instance, so that
        :meth:`.as_mutable` can be used inline::

            Table(
                "mytable",
                metadata,
                Column("id", Integer, primary_key=True),
                Column("data", MyMutableType.as_mutable(PickleType)),
            )

        Note that the returned type is always an instance, even if a class
        is given, and that only columns which are declared specifically with
        that type instance receive additional instrumentation.

        To associate a particular mutable type with all occurrences of a
        particular type, use the :meth:`.Mutable.associate_with` classmethod
        of the particular :class:`.Mutable` subclass to establish a global
        association.

        .. warning::

           The listeners established by this method are *global*
           to all mappers, and are *not* garbage collected.   Only use
           :meth:`.as_mutable` for types that are permanent to an application,
           not with ad-hoc types else this will cause unbounded growth
           in memory usage.

        """
        sqltype = types.to_instance(sqltype)

        # a SchemaType will be copied when the Column is copied,
        # and we'll lose our ability to link that type back to the original.
        # so track our original type w/ columns
        if isinstance(sqltype, SchemaEventTarget):

            @event.listens_for(sqltype, "before_parent_attach")
            def _add_column_memo(
                sqltyp: TypeEngine[Any],
                parent: Column[_T],
            ) -> None:
                parent.info["_ext_mutable_orig_type"] = sqltyp

            schema_event_check = True
        else:
            schema_event_check = False

        def listen_for_type(
            mapper: Mapper[_T],
            class_: Union[DeclarativeAttributeIntercept, type],
        ) -> None:
            if mapper.non_primary:
                return