Method defer

lib/sqlalchemy/orm/strategy_options.py:581–640

r"""Indicate that the given column-oriented attribute should be deferred, e.g. not loaded until accessed. This function is part of the :class:`_orm.Load` interface and supports both method-chained and standalone operation. e.g.:: from sqlalchemy.orm imp

(self, key: _AttrType, raiseload: bool = False)

        return self._set_relationship_strategy(attr, None)

    def defer(self, key: _AttrType, raiseload: bool = False) -> Self:
        r"""Indicate that the given column-oriented attribute should be
        deferred, e.g. not loaded until accessed.

        This function is part of the :class:`_orm.Load` interface and supports
        both method-chained and standalone operation.

        e.g.::

            from sqlalchemy.orm import defer

            session.query(MyClass).options(
                defer(MyClass.attribute_one), defer(MyClass.attribute_two)
            )

        To specify a deferred load of an attribute on a related class,
        the path can be specified one token at a time, specifying the loading
        style for each link along the chain.  To leave the loading style
        for a link unchanged, use :func:`_orm.defaultload`::

            session.query(MyClass).options(
                defaultload(MyClass.someattr).defer(RelatedClass.some_column)
            )

        Multiple deferral options related to a relationship can be bundled
        at once using :meth:`_orm.Load.options`::


            select(MyClass).options(
                defaultload(MyClass.someattr).options(
                    defer(RelatedClass.some_column),
                    defer(RelatedClass.some_other_column),
                    defer(RelatedClass.another_column),
                )
            )

        :param key: Attribute to be deferred.

        :param raiseload: raise :class:`.InvalidRequestError` rather than
         lazy loading a value when the deferred attribute is accessed. Used
         to prevent unwanted SQL from being emitted.

        .. versionadded:: 1.4

        .. seealso::

            :ref:`orm_queryguide_column_deferral` - in the
            :ref:`queryguide_toplevel`

            :func:`_orm.load_only`

            :func:`_orm.undefer`

        """
        strategy = {"deferred": True, "instrument": True}
        if raiseload:
            strategy["raiseload"] = True
        return self._set_column_strategy(