Class _ScalarObjectAttributeImpl

lib/sqlalchemy/orm/attributes.py:1339–1550

represents a scalar-holding InstrumentedAttribute, where the target object is also instrumented. Adds events to delete/set operations.

class _ScalarObjectAttributeImpl(_ScalarAttributeImpl):
    """represents a scalar-holding InstrumentedAttribute,
    where the target object is also instrumented.

    Adds events to delete/set operations.

    """

    default_accepts_scalar_loader = False
    uses_objects = True
    supports_population = True
    collection = False

    __slots__ = ()

    def delete(self, state: InstanceState[Any], dict_: _InstanceDict) -> None:
        if self.dispatch._active_history:
            old = self.get(
                state,
                dict_,
                passive=PASSIVE_ONLY_PERSISTENT
                | NO_AUTOFLUSH
                | LOAD_AGAINST_COMMITTED,
            )
        else:
            old = self.get(
                state,
                dict_,
                passive=PASSIVE_NO_FETCH ^ INIT_OK
                | LOAD_AGAINST_COMMITTED
                | NO_RAISE,
            )

        self.fire_remove_event(state, dict_, old, self._remove_token)

        existing = dict_.pop(self.key, NO_VALUE)

        # if the attribute is expired, we currently have no way to tell
        # that an object-attribute was expired vs. not loaded.   So
        # for this test, we look to see if the object has a DB identity.
        if (
            existing is NO_VALUE
            and old is not PASSIVE_NO_RESULT
            and state.key is None
        ):
            raise AttributeError("%s object does not have a value" % self)

    def get_history(
        self,
        state: InstanceState[Any],
        dict_: _InstanceDict,
        passive: PassiveFlag = PASSIVE_OFF,
    ) -> History:
        if self.key in dict_:
            current = dict_[self.key]
        else:
            if passive & INIT_OK:
                passive ^= INIT_OK