Fix race condition when requesting songs, causing them to get the same order value.

marietje/queues/migrations/0004_remove_playlistsong_order.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.5 on 2017-09-23 22:59
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('queues', '0003_queuecommand'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='playlistsong',
+            name='order',
+        ),
+    ]

marietje/queues/models.py

@@ -36,22 +36,20 @@ class PlaylistSong(models.Model):
     # 3: Cancelled.
     state = models.IntegerField(default=0)
 
-    order = models.IntegerField()
-
     def move_up(self):
-        other_song = PlaylistSong.objects.filter(playlist=self.playlist, order__lt=self.order)\
+        other_song = PlaylistSong.objects.filter(playlist=self.playlist, id__lt=self.id)\
-            .order_by('-order').first()
+            .order_by('-id').first()
         self.switch_order(other_song)
 
     def move_down(self):
-        other_song = PlaylistSong.objects.filter(playlist=self.playlist, order__gt=self.order).order_by('order').first()
+        other_song = PlaylistSong.objects.filter(playlist=self.playlist, id__gt=self.id).order_by('id').first()
         self.switch_order(other_song)
 
     def switch_order(self, other_song):
-        old_order = self.order
+        old_id = self.id
-        self.order = other_song.order
+        self.id = other_song.id
+        other_song.id = old_id
         self.save()
-        other_song.order = old_order
         other_song.save()
 
     def __str__(self):
@@ -91,7 +89,7 @@ class Queue(models.Model):
             self.songs = PlaylistSong.objects\
                 .filter(Q(playlist=self.playlist_id) | Q(playlist_id=self.random_playlist_id),
                         Q(state=0) | Q(state=1))\
-                .order_by('-state', 'playlist_id', 'order')\
+                .order_by('-state', 'playlist_id', 'id')\
                 .select_related('song', 'user')
         return self.songs
 
@@ -112,12 +110,10 @@ class Queue(models.Model):
         return songs[1:]
 
     def request(self, song, user):
-        playlist_songs = PlaylistSong.objects.filter(playlist=self.playlist, state=0).order_by('order')
+        playlist_songs = PlaylistSong.objects.filter(playlist=self.playlist, state=0).order_by('id')
 
-        order = 0
         seconds_in_a_row = 0
         for playlist_song in playlist_songs:
-            order = playlist_song.order
             if playlist_song.user != user:
                 seconds_in_a_row = 0
             else:
@@ -129,27 +125,17 @@ class Queue(models.Model):
                     and not user.is_superuser and settings.LIMIT_HOURS[0] <= now.hour < settings.LIMIT_HOURS[1]:
                 return False
 
-        if order is None:
+        playlist_song = PlaylistSong(playlist=self.playlist, song=song, user=user)
-            order = 0
-        order += 1
-        playlist_song = PlaylistSong(playlist=self.playlist, song=song, user=user, order=order)
         playlist_song.save()
         return True
 
     def fill_random_queue(self):
         song_count = PlaylistSong.objects.filter(playlist_id=self.random_playlist_id, state=0).count()
         while song_count < 5:
-            order = PlaylistSong.objects.filter(playlist_id=self.random_playlist_id)\
-                .aggregate(Max('order'))['order__max']
-            if order is None:
-                order = 0
-            order += 1
             song = Song.objects.filter(deleted=False).order_by('?').first()
             if song is None:
                 return
-            playlist_song = PlaylistSong(playlist=self.random_playlist,
+            playlist_song = PlaylistSong(playlist=self.random_playlist, song=song, user=None)
-                                         song=song,
-                                         user=None, order=order)
             playlist_song.save()
             song_count += 1