models: Fix equality for fields set to the default

Fixes #837

(cherry picked from commit bdd1fb983b)

docs/changelog.rst

@@ -10,6 +10,12 @@ v0.19.5 (UNRELEASED)
 
 - Models: Hide empty collections from :func:`repr()` representations.
 
+- Field values are no longer stored on the model instance when the value
+  matches the default value for the field. This makes two models equal when
+  they have a field which in one case is implicitly set to the default value
+  and in the other case explicitly set to the default value, but with otherwise
+  equal fields. (Fixes: :issue:`837`)
+
 
 v0.19.4 (2014-09-01)
 ====================

mopidy/models.py

@@ -18,6 +18,8 @@ class ImmutableObject(object):
                 raise TypeError(
                     '__init__() got an unexpected keyword argument "%s"' %
                     key)
+            if value == getattr(self, key):
+                continue  # Don't explicitly set default values
             self.__dict__[key] = value
 
     def __setattr__(self, name, value):
@@ -72,13 +74,11 @@ class ImmutableObject(object):
         for key in self.__dict__.keys():
             public_key = key.lstrip('_')
             value = values.pop(public_key, self.__dict__[key])
-            if value is not None:
-                data[public_key] = value
+            data[public_key] = value
         for key in values.keys():
             if hasattr(self, key):
                 value = values.pop(key)
-                if value is not None:
-                    data[key] = value
+                data[key] = value
         if values:
             raise TypeError(
                 'copy() got an unexpected keyword argument "%s"' % key)

tests/test_models.py

@@ -171,8 +171,8 @@ class ArtistTest(unittest.TestCase):
 
     def test_serialize_falsy_values(self):
         self.assertDictEqual(
-            {'__model__': 'Artist', 'uri': '', 'name': None},
-            Artist(uri='', name=None).serialize())
+            {'__model__': 'Artist', 'uri': '', 'name': ''},
+            Artist(uri='', name='').serialize())
 
     def test_to_json_and_back(self):
         artist1 = Artist(uri='uri', name='name')
@@ -735,6 +735,24 @@ class TrackTest(unittest.TestCase):
         self.assertNotEqual(track1, track2)
         self.assertNotEqual(hash(track1), hash(track2))
 
+    def test_ignores_values_with_default_value_none(self):
+        track1 = Track(name='name1')
+        track2 = Track(name='name1', album=None)
+        self.assertEqual(track1, track2)
+        self.assertEqual(hash(track1), hash(track2))
+
+    def test_ignores_values_with_default_value_zero(self):
+        track1 = Track(name='name1')
+        track2 = Track(name='name1', track_no=0)
+        self.assertEqual(track1, track2)
+        self.assertEqual(hash(track1), hash(track2))
+
+    def test_copy_can_reset_to_default_value(self):
+        track1 = Track(name='name1')
+        track2 = Track(name='name1', album=Album()).copy(album=None)
+        self.assertEqual(track1, track2)
+        self.assertEqual(hash(track1), hash(track2))
+
 
 class TlTrackTest(unittest.TestCase):
     def test_tlid(self):