From 59a06a242d5d7681bac6280291ba1c97f5f2b621 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bastien=20G=C3=A9rard?= <bastien.gerard@cluepoints.com>
Date: Mon, 15 Oct 2018 22:32:11 +0200
Subject: [PATCH] Fix a bug when using a ReferenceField(AbstractClass) #1920

---
 mongoengine/fields.py         |  9 -------
 tests/document/inheritance.py | 48 +++++++++++++++++++++++++++++------
 2 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index 04e89256..284c614d 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -1176,15 +1176,6 @@ class ReferenceField(BaseField):
             self.error('You can only reference documents once they have been '
                        'saved to the database')
 
-        if (
-            self.document_type._meta.get('abstract') and
-            not isinstance(value, self.document_type)
-        ):
-            self.error(
-                '%s is not an instance of abstract reference type %s' % (
-                    value, self.document_type._class_name)
-            )
-
     def lookup_member(self, member_name):
         return self.document_type._fields.get(member_name)
 
diff --git a/tests/document/inheritance.py b/tests/document/inheritance.py
index b2ab1b52..735c68da 100644
--- a/tests/document/inheritance.py
+++ b/tests/document/inheritance.py
@@ -2,14 +2,11 @@
 import unittest
 import warnings
 
-from datetime import datetime
-
 from tests.fixtures import Base
 
-from mongoengine import Document, EmbeddedDocument, connect
+from mongoengine import Document, EmbeddedDocument, connect, ReferenceField,\
+    BooleanField, GenericReferenceField, IntField, StringField
 from mongoengine.connection import get_db
-from mongoengine.fields import (BooleanField, GenericReferenceField,
-                                IntField, StringField)
 
 __all__ = ('InheritanceTest', )
 
@@ -300,6 +297,41 @@ class InheritanceTest(unittest.TestCase):
         doc = Animal(name='dog')
         self.assertNotIn('_cls', doc.to_mongo())
 
+    def test_using_abstract_class_in_reference_field(self):
+        # Ensures no regression of #1920
+        class AbstractHuman(Document):
+            meta = {'abstract': True}
+
+        class Dad(AbstractHuman):
+            name = StringField()
+
+        class Home(Document):
+            dad = ReferenceField(AbstractHuman)  # Referencing the abstract class
+            address = StringField()
+
+        dad = Dad(name='5').save()
+        Home(dad=dad, address='street').save()
+
+        home = Home.objects.first()
+        home.address = 'garbage'
+        home.save()     # Was failing with ValidationError
+
+    def test_abstract_class_referencing_self(self):
+        # Ensures no regression of #1920
+        class Human(Document):
+            meta = {'abstract': True}
+            creator = ReferenceField('self', dbref=True)
+
+        class User(Human):
+            name = StringField()
+
+        user = User(name='John').save()
+        user2 = User(name='Foo', creator=user).save()
+
+        user2 = User.objects.with_id(user2.id)
+        user2.name = 'Bar'
+        user2.save()    # Was failing with ValidationError
+
     def test_abstract_handle_ids_in_metaclass_properly(self):
 
         class City(Document):
@@ -358,11 +390,11 @@ class InheritanceTest(unittest.TestCase):
             meta = {'abstract': True,
                     'allow_inheritance': False}
 
-        bkk = City(continent='asia')
-        self.assertEqual(None, bkk.pk)
+        city = City(continent='asia')
+        self.assertEqual(None, city.pk)
         # TODO: expected error? Shouldn't we create a new error type?
         with self.assertRaises(KeyError):
-            setattr(bkk, 'pk', 1)
+            setattr(city, 'pk', 1)
 
     def test_allow_inheritance_embedded_document(self):
         """Ensure embedded documents respect inheritance."""