item fields no longer dirtied if unchanged when assigned

This is especially important for read(), which will assign many times while, in many cases, causing few actual changes. A store() that follows soon after will now be much more lightweight.

--HG--
extra : convert_revision : svn%3A41726ec3-264d-0410-9c23-a9f1637257cc/trunk%4079

beets/library.py

@@ -121,8 +121,10 @@ class Item(object):
         Otherwise, performs an ordinary setattr."""
         
         if key in item_keys:
-            self.record[key] = value
-            self.dirty[key] = True
+            if (not (key in self.record)) or (self.record[key] != value):
+                # don't dirty if value unchanged
+                self.record[key] = value
+                self.dirty[key] = True
         else:
             object.__setattr__(self, key, value)
     

test/test_db.py

@@ -117,8 +117,12 @@ class GetSetTest(unittest.TestCase):
         self.assertEqual(self.i.bpm, 4915)
     
     def test_set_sets_dirty_flag(self):
-        self.i.comp = True
+        self.i.comp = not self.i.comp
         self.assertTrue(self.i.dirty['comp'])
+    
+    def test_set_does_not_dirty_if_value_unchanged(self):
+        self.i.title = self.i.title
+        self.assertTrue(not self.i.dirty['title'])
 
 class DestinationTest(unittest.TestCase):
     def setUp(self):