local: Add support for list_distinct and implement for json backend

mopidy/local/__init__.py

@@ -89,6 +89,18 @@ class Library(object):
         """
         raise NotImplementedError
 
+    def list_distinct(self, field, query=None):
+        """
+        List distinct values for a given field from the library.
+
+        :param string field: One of ``artist``, ``albumartist``, ``album``,
+            ``composer``, ``performer``, ``date``or ``genre``.
+        :param dict query: Query to use for limiting results, see
+            :method:`search` for details about the query format.
+        :rtype: set of values corresponding to the requested field type.
+        """
+        return set()
+
     def load(self):
         """
         (Re)load any tracks stored in memory, if any, otherwise just return

mopidy/local/json.py

@@ -155,6 +155,38 @@ class JsonLibrary(local.Library):
         except KeyError:
             return []
 
+    def list_distinct(self, field, query=None):
+        if field == 'artist':
+            def distinct(track):
+                return {a.name for a in track.artists}
+        elif field == 'albumartist':
+            def distinct(track):
+                album = track.album or models.Album()
+                return {a.name for a in album.artists}
+        elif field == 'album':
+            def distinct(track):
+                album = track.album or models.Album()
+                return {album.name}
+        elif field == 'composer':
+            def distinct(track):
+                return {a.name for a in track.composers}
+        elif field == 'performer':
+            def distinct(track):
+                return {a.name for a in track.performers}
+        elif field == 'date':
+            def distinct(track):
+                return {track.date}
+        elif field == 'genre':
+            def distinct(track):
+                return {track.genre}
+        else:
+            return set()
+
+        result = set()
+        for track in search.search(self._tracks.values(), query).tracks:
+            result.update(distinct(track))
+        return result
+
     def search(self, query=None, limit=100, offset=0, uris=None, exact=False):
         tracks = self._tracks.values()
         # TODO: pass limit and offset into search helpers

mopidy/local/library.py

@@ -23,6 +23,11 @@ class LocalLibraryProvider(backend.LibraryProvider):
             return []
         return self._library.browse(uri)
 
+    def list_distinct(self, field, query=None):
+        if not self._library:
+            return set()
+        return self._library.list_distinct(field, query)
+
     def refresh(self, uri=None):
         if not self._library:
             return 0