added test for abstract document without pk creation and adapted behaviour

mongoengine/base/document.py

@@ -184,7 +184,7 @@ class BaseDocument(object):
             self__initialised = False
         # Check if the user has created a new instance of a class
         if (self._is_document and self__initialised
-                and self__created and name == self._meta['id_field']):
+                and self__created and name == self._meta.get('id_field')):
             super(BaseDocument, self).__setattr__('_created', False)
 
         super(BaseDocument, self).__setattr__(name, value)

mongoengine/document.py

@@ -152,6 +152,8 @@ class Document(BaseDocument):
         """
 
         def fget(self):
+            if not 'id_field' in self._meta:
+                return None
             return getattr(self, self._meta['id_field'])
 
         def fset(self, value):

tests/document/inheritance.py

@@ -307,6 +307,17 @@ class InheritanceTest(unittest.TestCase):
         doc = Animal(name='dog')
         self.assertFalse('_cls' in doc.to_mongo())
 
+    def test_abstract_document_creation_does_not_fail(self):
+
+        class City(Document):
+            continent = StringField()
+            meta = {'abstract': True,
+                    'allow_inheritance': False}
+        bkk = City(continent='asia')
+        self.assertEqual(None, bkk.pk)
+        # TODO: expected error? Shouldn'twe created a new error type
+        self.assertRaises(KeyError, lambda: setattr(bkk, 'pk', 1))
+
     def test_allow_inheritance_embedded_document(self):
         """Ensure embedded documents respect inheritance
         """