Method init_collection

lib/sqlalchemy/orm/events.py:2948–2989

Receive a 'collection init' event. This event is triggered for a collection-based attribute, when the initial "empty collection" is first generated for a blank attribute, as well as for when the collection is replaced with a new one, such as via a set event.

(
        self,
        target: _O,
        collection: Type[Collection[Any]],
        collection_adapter: CollectionAdapter,
    )

        """  # noqa: E501

    def init_collection(
        self,
        target: _O,
        collection: Type[Collection[Any]],
        collection_adapter: CollectionAdapter,
    ) -> None:
        """Receive a 'collection init' event.

        This event is triggered for a collection-based attribute, when
        the initial "empty collection" is first generated for a blank
        attribute, as well as for when the collection is replaced with
        a new one, such as via a set event.

        E.g., given that ``User.addresses`` is a relationship-based
        collection, the event is triggered here::

            u1 = User()
            u1.addresses.append(a1)  #  <- new collection

        and also during replace operations::

            u1.addresses = [a2, a3]  #  <- new collection

        :param target: the object instance receiving the event.
         If the listener is registered with ``raw=True``, this will
         be the :class:`.InstanceState` object.
        :param collection: the new collection.  This will always be generated
         from what was specified as
         :paramref:`_orm.relationship.collection_class`, and will always
         be empty.
        :param collection_adapter: the :class:`.CollectionAdapter` that will
         mediate internal access to the collection.

        .. seealso::

            :class:`.AttributeEvents` - background on listener options such
            as propagation to subclasses.

            :meth:`.AttributeEvents.init_scalar` - "scalar" version of this
            event.

        """

    def dispose_collection(
        self,