Method from_collection

lib/sqlalchemy/orm/attributes.py:2486–2518

(
        cls,
        attribute: CollectionAttributeImpl,
        state: InstanceState[Any],
        current: Any,
    )

    @classmethod
    def from_collection(
        cls,
        attribute: CollectionAttributeImpl,
        state: InstanceState[Any],
        current: Any,
    ) -> History:
        original = state.committed_state.get(attribute.key, _NO_HISTORY)
        if current is NO_VALUE:
            return cls((), (), ())

        current = getattr(current, "_sa_adapter")
        if original is NO_VALUE:
            return cls(list(current), (), ())
        elif original is _NO_HISTORY:
            return cls((), list(current), ())
        else:
            current_states = [
                ((c is not None) and instance_state(c) or None, c)
                for c in current
            ]
            original_states = [
                ((c is not None) and instance_state(c) or None, c)
                for c in original
            ]

            current_set = dict(current_states)
            original_set = dict(original_states)

            return cls(
                [o for s, o in current_states if s not in original_set],
                [o for s, o in current_states if s in original_set],
                [o for s, o in original_states if s not in current_set],
            )


HISTORY_BLANK = History((), (), ())