Made type inheritance a validation check for abstract references

mongoengine/fields.py

@@ -996,6 +996,14 @@ 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._class_name,
+                        self.document_type._class_name)
+                    )
+
+
     def lookup_member(self, member_name):
         return self.document_type._fields.get(member_name)
 

tests/fields/fields.py

@@ -2331,6 +2331,31 @@ class FieldTest(unittest.TestCase):
         Sister.drop_collection()
         Brother.drop_collection()
 
+    def test_abstract_reference_base_type(self):
+        """Ensure that an an abstract reference fails validation when given a
+        Document that does not inherit from the abstract type.
+        """
+        class Sibling(Document):
+            name = StringField()
+            meta = {"abstract": True}
+
+        class Brother(Sibling):
+            sibling = ReferenceField(Sibling)
+
+        class Mother(Document):
+            name = StringField()
+
+        Brother.drop_collection()
+        Mother.drop_collection()
+
+        mother = Mother(name="Carol")
+        mother.save()
+        brother = Brother(name="Bob", sibling=mother)
+        self.assertRaises(ValidationError, brother.save)
+
+        Brother.drop_collection()
+        Mother.drop_collection()
+
     def test_generic_reference(self):
         """Ensure that a GenericReferenceField properly dereferences items.
         """