Fixed cascade save edge case

refs MongoEngine/mongoengine#40

docs/changelog.rst

@@ -4,6 +4,7 @@ Changelog
 
 Changes in 0.6.15
 =================
+- Fixed cascade save edge case
 - Fixed geo index creation through reference fields
 - Added support for args / kwargs when using @queryset_manager
 - Deref list custom id fix

mongoengine/document.py

@@ -248,11 +248,16 @@ class Document(BaseDocument):
         _refs = kwargs.get('_refs', []) or []
 
         for name, cls in self._fields.items():
+
             if not isinstance(cls, (ReferenceField, GenericReferenceField)):
                 continue
+
             ref = getattr(self, name)
             if not ref:
                 continue
+            if isinstance(ref, DBRef):
+                continue
+
             ref_id = "%s,%s" % (ref.__class__.__name__, str(ref._data))
             if ref and ref_id not in _refs:
                 _refs.append(ref_id)

tests/test_document.py

@@ -3186,5 +3186,29 @@ name: Field is required ("name")"""
         p = Person(age=15)
         self.assertRaises(ValidationError, p.validate)
 
+    def test_cascaded_save_wrong_reference(self):
+
+        class ADocument(Document):
+            val = IntField()
+
+        class BDocument(Document):
+            a = ReferenceField(ADocument)
+
+        ADocument.drop_collection()
+        BDocument.drop_collection()
+
+        a = ADocument()
+        a.val = 15
+        a.save()
+
+        b = BDocument()
+        b.a = a
+        b.save()
+
+        a.delete()
+
+        b = BDocument.objects.first()
+        b.save(cascade=True)
+
 if __name__ == '__main__':
     unittest.main()