to_db_fields fix (#1553)

tests/queryset/field_list.py

@@ -197,14 +197,18 @@ class OnlyExcludeAllTest(unittest.TestCase):
             title = StringField()
             text = StringField()
 
+        class VariousData(EmbeddedDocument):
+            some = BooleanField()
+
         class BlogPost(Document):
             content = StringField()
             author = EmbeddedDocumentField(User)
             comments = ListField(EmbeddedDocumentField(Comment))
+            various = MapField(field=EmbeddedDocumentField(VariousData))
 
         BlogPost.drop_collection()
 
-        post = BlogPost(content='Had a good coffee today...')
+        post = BlogPost(content='Had a good coffee today...', various={'test_dynamic':{'some': True}})
         post.author = User(name='Test User')
         post.comments = [Comment(title='I aggree', text='Great post!'), Comment(title='Coffee', text='I hate coffee')]
         post.save()
@@ -215,6 +219,9 @@ class OnlyExcludeAllTest(unittest.TestCase):
         self.assertEqual(obj.author.name, 'Test User')
         self.assertEqual(obj.comments, [])
 
+        obj = BlogPost.objects.only('various.test_dynamic.some').get()
+        self.assertEqual(obj.various["test_dynamic"].some, True)
+
         obj = BlogPost.objects.only('content', 'comments.title',).get()
         self.assertEqual(obj.content, 'Had a good coffee today...')
         self.assertEqual(obj.author, None)