test_no_dereference_context_manager_object_id not working

[clysto]

test_no_dereference_context_manager_object_id:

mongoengine/tests/test_context_managers.py

Lines 119 to 154 in 9680259

	def test_no_dereference_context_manager_object_id(self):
	"""Ensure that DBRef items in ListFields aren't dereferenced."""
	connect("mongoenginetest")
	class User(Document):
	name = StringField()
	class Group(Document):
	ref = ReferenceField(User, dbref=False)
	generic = GenericReferenceField()
	members = ListField(ReferenceField(User, dbref=False))
	User.drop_collection()
	Group.drop_collection()
	for i in range(1, 51):
	User(name="user %s" % i).save()
	user = User.objects.first()
	Group(ref=user, members=User.objects, generic=user).save()
	with no_dereference(Group) as NoDeRefGroup:
	assert Group._fields["members"]._auto_dereference
	assert not NoDeRefGroup._fields["members"]._auto_dereference
	with no_dereference(Group) as Group:
	group = Group.objects.first()
	for m in group.members:
	assert not isinstance(m, User)
	assert not isinstance(group.ref, User)
	assert not isinstance(group.generic, User)
	for m in group.members:
	assert isinstance(m, User)
	assert isinstance(group.ref, User)
	assert isinstance(group.generic, User)

run this test:

pytest tests/test_context_managers.py -k "test_no_dereference_context_manager_object_id"

we got no error, but if I put the assert False in with no_dereference(Group) as Group::

        user = User.objects.first()
        Group(ref=user, members=User.objects, generic=user).save()

        with no_dereference(Group) as NoDeRefGroup:
            assert False # <--------
            assert Group._fields["members"]._auto_dereference
            assert not NoDeRefGroup._fields["members"]._auto_dereference

pytest shows that there are still no errors!!!

I think this is because the context manager causes the error to not be caught normally

[clysto]

mongoengine/mongoengine/context_managers.py

Lines 137 to 141 in 9680259

	def __exit__(self, t, value, traceback):
	"""Reset the default and _auto_dereference values."""
	for field in self.deref_fields:
	self.cls._fields[field]._auto_dereference = True
	return self.cls

returned value self.cls suppress the exception.

if i remove the return statement, rerun the test:

the pytest shows that Group._fields["members"]._auto_dereference is actually False. This is because the Group class and NoRefGroup class are the same class.

[bagerard]

Just seeing this now, good catch!. Indeed it's due to the faulty return in exit and existing tests were actually failing. The feature was actually quite broken 😬