feat: handle playlist_id according to the new field name

program/serializers.py

@@ -969,6 +969,13 @@ class TimeSlotSerializer(serializers.ModelSerializer):
         source="repetition_of",
         help_text="This timeslot is a repetition of `Timeslot` ID.",
     )
+    playlist_id = serializers.PrimaryKeyRelatedField(
+        allow_null=True,
+        help_text="",
+        queryset=Playlist.objects.all(),
+        required=False,
+        source="playlist",
+    )
 
     class Meta:
         model = TimeSlot
@@ -1024,7 +1031,7 @@ class TimeSlotSerializer(serializers.ModelSerializer):
             instance.repetition_of = validated_data.get("repetition_of")
 
         if "playlist_id" in validated_data:
-            instance.playlist_id = validated_data.get("playlist_id")
+            instance.playlist = validated_data.get("playlist_id")
 
         instance.save()