models.py

from django.db import models
from django.utils import timezone

from mptt.models import MPTTModel, TreeOneToOneField


class Playlist(models.Model):
    name = models.CharField(max_length=50)
    is_public = models.BooleanField(default=False)
    user = models.ForeignKey('users.User', related_name="playlists")
    creation_date = models.DateTimeField(default=timezone.now)

    def __str__(self):
        return self.name

    def add_track(self, track, previous=None):
        plt = PlaylistTrack(previous=previous, track=track, playlist=self)
        plt.save()

        return plt


class PlaylistTrack(MPTTModel):
    track = models.ForeignKey('music.Track', related_name='playlist_tracks')
    previous = TreeOneToOneField('self', blank=True, null=True, related_name='next')
    playlist = models.ForeignKey(Playlist, related_name='playlist_tracks')

    class MPTTMeta:
        level_attr = 'position'
        parent_attr = 'previous'

    class Meta:
        ordering = ('-playlist', 'position')