Fixes scalar lookups for primary_key

fixes hmarr/mongoengine#519

docs/changelog.rst

@@ -4,6 +4,7 @@ Changelog
 
 Changes in 0.6.X
 ================
+- Fixes scalar lookups for primary_key
 - Fixes error with _delta handling DBRefs
 
 Changes in 0.6.11

mongoengine/queryset.py

@@ -1496,8 +1496,6 @@ class QuerySet(object):
         def lookup(obj, name):
             chunks = name.split('__')
             for chunk in chunks:
-                if hasattr(obj, '_db_field_map'):
-                    chunk = obj._db_field_map.get(chunk, chunk)
                 obj = getattr(obj, chunk)
             return obj
 

tests/test_queryset.py

@@ -3006,6 +3006,19 @@ class QuerySetTest(unittest.TestCase):
         self.assertEqual(plist[1], (20, False))
         self.assertEqual(plist[2], (30, True))
 
+    def test_scalar_primary_key(self):
+
+        class SettingValue(Document):
+            key = StringField(primary_key=True)
+            value = StringField()
+
+        SettingValue.drop_collection()
+        s = SettingValue(key="test", value="test value")
+        s.save()
+
+        val = SettingValue.objects.scalar('key', 'value')
+        self.assertEqual(list(val), [('test', 'test value')])
+
     def test_scalar_cursor_behaviour(self):
         """Ensure that a query returns a valid set of results.
         """