django - 如何展平 django-rest-framework 序列化程序中的对象列表？

Question

我有 3 个由 ForeignKey 连接的 django 模型:

# models.py
class Album(models.Model):
    some_fields

class Track(models.Model):
    some_fields
    album = models.ForeignKey(
        Album,
        related_name='tracks',
        on_delete=models.CASCADE,
    )

class Comment(models.Model):
    some_fields
    track = models.ForeignKey(
        Track,
        related_name='comments',
        on_delete=models.CASCADE,
    )

我想序列化专辑模型以查看其所有轨道的所有评论。我创建了这样的序列化程序文件:

# serializers.py
class TrackSerializer(serializers.ModelSerializer):

    class Meta:
        model = Album
        fields = (some_fields, 'comments')

class AlbumSerializer(serializers.ModelSerializer):
    tracks = TrackSerializer(many=True, read_only=True)

    class Meta:
        model = Album
        fields = (some_fields, 'tracks')

通过这种方式，我获得了所有数据，但在嵌套列表中。我想直接在专辑对象下查看专辑轨道的所有评论。

# Output albums
[{
    "some_fields": some_values,
    "tracks": [{ "some_fields": some_values, "comments": [ comment1, comment2 ]},
            { "some_fields": some_values, "comments": []},
            { "some_fields": some_values, "comments": [ comment3 ]},]
},
{
    "some_fields": some_values,
    "tracks": [{ "some_fields": some_values, "comments": [ comment4, comment5 ]},
            { "some_fields": some_values, "comments": []},
            { "some_fields": some_values, "comments": [ comment6 ]},]
}]

# Desired output albums
[{
    "some_fields": some_values,
    "tracks": [{ "some_fields": some_values},
            { "some_fields": some_values},
            { "some_fields": some_values},],
    "comments": [ comment1, comment2, comment3]
},
{
    "some_fields": some_values,
    "tracks": [{ "some_fields": some_values},
            { "some_fields": some_values},
            { "some_fields": some_values},],
    "comments": [ comment4, comment5, comment6]
}]

我试图直接在序列化程序文件中展平列表，但我得到“类型错误:‘ListSerializer’对象不可迭代”。

# serializers.py
class AlbumSerializer(serializers.ModelSerializer):
    tracks = TrackSerializer(many=True, read_only=True)
    comments = [comment for track in tracks for comment in track.comments]

    class Meta:
        model = Album
        fields = (some_fields, 'tracks', 'comments')

有没有什么巧妙的方法可以直接用序列化程序输出扁平化的列表？或者我应该稍后在 views.py 中做？现在它看起来像这样:

# views.py
class AlbumMixin(object):
    model = Album
    raise_exception = True
    serializer_class = AlbumSerializer

    def get_queryset(self):
        return Album.objects.all()

class AlbumList(AlbumMixin, generics.ListCreateAPIView):
    pass

Answer 1

您可以在 AlbumSerializer 上添加一个 serializers.SerializerMethodField 并返回必要的注释。

像这样:

class CommentSerializer(serializers.ModelSerializer):
    class Meta:
        model = Comment
        fields = "__all__"


class AlbumSerializer(serializers.ModelSerializer):
    comments = serializers.SerializerMethodField()
    tracks = TrackSerializer(many=True, read_only=True)

    class Meta:
        model = Album
        fields = (some_fields, "comments", "tracks")

    def get_comments(self, obj):
        comments = Comment.objects.filter(track__in=obj.tracks.all())
        return CommentSerializer(comments, many=True).data
        # or you can get rid of CommentSerializer
        # return comments.values("some_field")

参见 SerializerMethodField 文档 here

更新

您可以使用@c6754 中的查询来改进查询

comments = Comment.objects.filter(track__album_id=obj.id)