db: Don't notify if the active-playlist doesn't change

This lets us skip a handful of database calls if we detect that we're
setting the active playlist to the same value.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

emmental/db/__init__.py

@@ -82,6 +82,8 @@ class Connection(connection.Connection):
 
     def set_active_playlist(self, plist: playlist.Playlist) -> None:
         """Set the currently active playlist."""
+        if self.active_playlist == plist:
+            return
         if self.active_playlist is not None:
             self.active_playlist.active = False
 

tests/db/test_db.py

@@ -114,6 +114,11 @@ class TestConnection(tests.util.TestCase):
         self.assertFalse(plist1.active)
         self.assertTrue(plist2.active)
 
+        notify = unittest.mock.Mock()
+        self.sql.connect("notify::active-playlist", notify)
+        self.sql.set_active_playlist(plist2)
+        notify.assert_not_called()
+
         self.sql.set_active_playlist(None)
         self.assertIsNone(self.sql.active_playlist)
         self.assertFalse(plist2.active)