'Only should work with DictField even if they have numeric keys.'

def test_dictfield_key_looks_like_a_digit(self):

    class MyDoc(Document, ):
        test = DictField()
    MyDoc.drop_collection()
    doc = MyDoc(test={'47': 1})
    doc.save()
    self.assertEqual(MyDoc.objects.only('test__47').get().test['47'], 1)
