Raise DoesNotExist when dereferencing unknown document

tests/fields/fields.py

@@ -31,7 +31,7 @@ from mongoengine import *
 from mongoengine.connection import get_db
 from mongoengine.base import _document_registry
 from mongoengine.base.datastructures import BaseDict, EmbeddedDocumentList
-from mongoengine.errors import NotRegistered
+from mongoengine.errors import NotRegistered, DoesNotExist
 from mongoengine.python_support import PY3, b, bin_type
 
 __all__ = ("FieldTest", "EmbeddedDocumentListFieldTestCase")
@@ -1726,6 +1726,37 @@ class FieldTest(unittest.TestCase):
 
         self.assertEqual(content, User.objects.first().groups[0].content)
 
+    def test_reference_miss(self):
+        """Ensure an exception is raised when dereferencing unknow document
+        """
+
+        class Foo(Document):
+            pass
+
+        class Bar(Document):
+            ref = ReferenceField(Foo)
+            generic_ref = GenericReferenceField()
+
+        Foo.drop_collection()
+        Bar.drop_collection()
+
+        foo = Foo().save()
+        bar = Bar(ref=foo, generic_ref=foo).save()
+
+        # Reference is no longer valid
+        foo.delete()
+        bar = Bar.objects.get()
+        self.assertRaises(DoesNotExist, lambda: getattr(bar, 'ref'))
+        self.assertRaises(DoesNotExist, lambda: getattr(bar, 'generic_ref'))
+
+        # When auto_dereference is disabled, there is no trouble returning DBRef
+        bar = Bar.objects.get()
+        expected = foo.to_dbref()
+        bar._fields['ref']._auto_dereference = False
+        self.assertEqual(bar.ref, expected)
+        bar._fields['generic_ref']._auto_dereference = False
+        self.assertEqual(bar.generic_ref, {'_ref': expected, '_cls': 'Foo'})
+
     def test_reference_validation(self):
         """Ensure that invalid docment objects cannot be assigned to reference
         fields.