Django音乐应用用户播放列表无法显示问题排查

我正在开发一个音乐流媒体网站，尝试在<div id="divId">中展示用户的播放列表，但页面始终显示“用户没有播放列表”，可数据库里明明存在对应用户的播放列表。问题出在哪？会不会是播放列表的视图逻辑有问题？

HTML代码 #

<div id="divId">
    {% if myPlaylists %}
        <p style="margin: 5px; font-size: 0.75rem; font-weight: 700; color: rgb(138, 138, 138); text-align: left;">Add This Song To Your Playlist</p>
    {% for playlist in myPlaylists %}
        <a class="left-panel-btn" id="D_{{playlist.playlist_id}}" onclick="sendPostRequestPlaylistSong(this)">{{playlistInfo.playlist_name}}</a><br>
    {% endfor %}
    {% else %}
        <p style="margin: 5px; font-size: 0.8rem; font-weight: 700; color: rgb(138, 138, 138); text-align: left;">You don't have any Playlist.</p>
        <a class="create-p" onclick="$('#divId').css({display: 'none'}); document.getElementById('modal-wrapper-playlist').style.display='block'"><i class="fas fa-plus"></i> Create Playlist</a>
    {% endif %}
</div>

Models.py代码 #

class Song(models.Model):
    song_id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=50)
    artist = models.CharField(max_length=50)
    album = models.CharField(max_length=50, blank=True)
    genre = models.CharField(max_length=20, blank=True, default='Album')
    song = models.FileField(upload_to="songs/", validators=[FileExtensionValidator(allowed_extensions=['mp3', 'wav'])], default="name")
    image = models.ImageField(upload_to="songimage/", validators=[FileExtensionValidator(allowed_extensions=['jpeg', 'jpg', 'png'])], default="https://placehold.co/300x300/png")
    data = models.DateTimeField(auto_now=False, auto_now_add=True)
    slug = models.SlugField()

    def __str__(self):
        return self.name

    class Meta:
        ordering = ['name']

class Playlist(models.Model):
    playlist_id = models.AutoField(primary_key=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    playlist_name = models.CharField(max_length=50, default="name")
    image = models.ImageField(upload_to="playlist_images/", validators=[FileExtensionValidator(allowed_extensions=['jpeg', 'jpg', 'png'])], default="media/images/music-placeholder.png")
    plays = models.IntegerField(default=0)
    songs = models.ManyToManyField(Song, related_name='playlist')
    slug = models.SlugField()

    def __str__(self):
        return self.playlist_name

Views.py代码 #

def playlist(request, playlist_id):
    user = request.user
    if user.is_authenticated:
        myPlaylists = Playlist.objects.filter(user=user)
        if request.method == "POST":
            song_id = request.POST["music_id"]
            playlist = Playlist.objects.filter(playlist_id=playlist_id).first()
            if song_id in playlist.songs.all():
                playlist.songs.remove(song_id)
                playlist.plays -= 1
                playlist.save()
            message = "Successfull"
            print(message)
            return HttpResponse(json.dumps({'message': message}))
        else:
            images = os.listdir("media/playlist_images")
            print(images)
            currPlaylist = Playlist.objects.filter(playlist_id=playlist_id).first()
            songs = currPlaylist.songs
            playlistSongs = [currPlaylist.songs.all()]
            recommendedSingers = []

            return render(request, "music/playlist.html", {'playlistInfo': currPlaylist,
                                                       'playlistSongs': playlistSongs,
                                                       'myPlaylists': myPlaylists,
                                                       'recommendedSingers': recommendedSingers})

以下是几个关键问题点及对应的修复方法：

1. 未处理用户未登录的边界情况

   • 当前视图仅在user.is_authenticated为True时才会查询myPlaylists并传递给模板，如果用户未登录，myPlaylists根本不会被传入模板，导致模板触发{% else %}分支，显示“无播放列表”。
   • 修复：在视图开头初始化空查询集，确保所有分支都能传递myPlaylists：

     def playlist(request, playlist_id):
         user = request.user
         myPlaylists = Playlist.objects.none()  # 默认空查询集
         if user.is_authenticated:
             myPlaylists = Playlist.objects.filter(user=user)
         # 后续代码保持不变，确保render或返回响应时都传递myPlaylists
     

2. 模板循环中的变量错误

   • HTML模板循环播放列表时，错误地使用了{{playlistInfo.playlist_name}}（当前单个播放列表的名称），而不是循环项{{playlist.playlist_name}}，即使播放列表能显示，也会重复显示同一个名称。
   • 修复：修改循环内的变量：

     {% for playlist in myPlaylists %}
         <a class="left-panel-btn" id="D_{{playlist.playlist_id}}" onclick="sendPostRequestPlaylistSong(this)">{{playlist.playlist_name}}</a><br>
     {% endfor %}
     

3. POST请求中歌曲存在判断逻辑错误

   • if song_id in playlist.songs.all()的写法错误：playlist.songs.all()返回的是Song对象列表，而song_id是从POST中获取的字符串ID，两者无法直接比较，导致判断永远为False。
   • 修复：改用exists()方法判断歌曲是否在播放列表中：

     song = Song.objects.get(song_id=song_id)
     if playlist.songs.filter(song_id=song_id).exists():
         playlist.songs.remove(song)
         playlist.plays -= 1
         playlist.save()
     

4. 播放列表歌曲数据格式问题

   • playlistSongs = [currPlaylist.songs.all()]将查询集包裹在列表中，会导致模板遍历困难，应该直接传递查询集本身。
   • 修复：

     playlistSongs = currPlaylist.songs.all()
     

5. 验证用户与播放列表的关联关系

   • 确认数据库中播放列表的user字段确实关联到当前登录的用户，可以在视图中添加调试打印：

     print(f"当前用户: {user.username}, 查询到的播放列表数量: {myPlaylists.count()}")
     

   • 如果打印结果显示数量为0，检查数据库中播放列表的用户关联是否正确。

内容的提问来源于stack exchange，提问作者Federico Monetti