Add support for multiple tags for multiple values (fixes #44)

mopidy_mpd/translator.py

@@ -42,7 +42,7 @@ def track_to_mpd_format(track, position=None, stream_title=None):
     result = [
         ("file", track.uri),
         ("Time", track.length and (track.length // 1000) or 0),
-        ("Artist", concat_multi_values(track.artists, "name")),
+        *multi_tag_list(track.artists, "name", "Artist"),
         ("Album", track.album and track.album.name or ""),
     ]
 
@@ -69,9 +69,8 @@ def track_to_mpd_format(track, position=None, stream_title=None):
         result.append(("MUSICBRAINZ_ALBUMID", track.album.musicbrainz_id))
 
     if track.album is not None and track.album.artists:
-        result.append(
-            ("AlbumArtist", concat_multi_values(track.album.artists, "name"))
-        )
+        result += multi_tag_list(track.album.artists, "name", "AlbumArtist")
+
         musicbrainz_ids = concat_multi_values(
             track.album.artists, "musicbrainz_id"
         )
@@ -84,14 +83,10 @@ def track_to_mpd_format(track, position=None, stream_title=None):
             result.append(("MUSICBRAINZ_ARTISTID", musicbrainz_ids))
 
     if track.composers:
-        result.append(
-            ("Composer", concat_multi_values(track.composers, "name"))
-        )
+        result += multi_tag_list(track.composers, "name", "Composer")
 
     if track.performers:
-        result.append(
-            ("Performer", concat_multi_values(track.performers, "name"))
-        )
+        result += multi_tag_list(track.performers, "name", "Performer")
 
     if track.genre:
         result.append(("Genre", track.genre))
@@ -151,6 +146,28 @@ def concat_multi_values(models, attribute):
     )
 
 
+def multi_tag_list(objects, attribute, tag):
+    """
+    Format multiple objects for output to MPD client in a list with one tag per
+    value.
+
+    :param objects: the model objects
+    :type objects: array of :class:`mopidy.models.Artist`,
+        :class:`mopidy.models.Album`, or :class:`mopidy.models.Track`
+    :param attribute: the attribute to use
+    :type attribute: string
+    :param tag: the name of the tag
+    :type tag: string
+    :rtype: list of tuples of string and attribute value
+    """
+
+    return [
+        (tag, getattr(obj, attribute))
+        for obj in objects
+        if getattr(obj, attribute, None) is not None
+    ]
+
+
 def tracks_to_mpd_format(tracks, start=0, end=None):
     """
     Format list of tracks for output to MPD client.

tests/test_translator.py

@@ -9,17 +9,23 @@
 class TrackMpdFormatTest(unittest.TestCase):
     track = Track(
         uri="à uri",
-        artists=[Artist(name="an artist")],
+        artists=[Artist(name="an artist"), Artist(name="yet another artist")],
         name="a nàme",
         album=Album(
             name="an album",
             num_tracks=13,
-            artists=[Artist(name="an other artist")],
+            artists=[
+                Artist(name="an other artist"),
+                Artist(name="still another artist"),
+            ],
             uri="urischeme:àlbum:12345",
         ),
         track_no=7,
-        composers=[Artist(name="a composer")],
-        performers=[Artist(name="a performer")],
+        composers=[Artist(name="a composer"), Artist(name="another composer")],
+        performers=[
+            Artist(name="a performer"),
+            Artist(name="another performer"),
+        ],
         genre="a genre",
         date="1977-01-01",
         disc_no=1,
@@ -69,11 +75,15 @@ def test_track_to_mpd_format_for_nonempty_track(self):
         assert ("file", "à uri") in result
         assert ("Time", 137) in result
         assert ("Artist", "an artist") in result
+        assert ("Artist", "yet another artist") in result
         assert ("Title", "a nàme") in result
         assert ("Album", "an album") in result
         assert ("AlbumArtist", "an other artist") in result
+        assert ("AlbumArtist", "still another artist") in result
         assert ("Composer", "a composer") in result
+        assert ("Composer", "another composer") in result
         assert ("Performer", "a performer") in result
+        assert ("Performer", "another performer") in result
         assert ("Genre", "a genre") in result
         assert ("Track", "7/13") in result
         assert ("Date", "1977-01-01") in result
@@ -82,7 +92,7 @@ def test_track_to_mpd_format_for_nonempty_track(self):
         assert ("Id", 122) in result
         assert ("X-AlbumUri", "urischeme:àlbum:12345") in result
         assert ("Comment", "a comment") not in result
-        assert len(result) == 15
+        assert len(result) == 19
 
     def test_track_to_mpd_format_with_last_modified(self):
         track = self.track.replace(last_modified=995303899000)