Django Rest API - 将 prefetch_related 与 ModelSerializer 一起使用

Question

每篇博文我都有一个评论栏。 我想将 Views.py 中的 Comment.objects.all() 传递给 ModelSerializer def get_cmets(self, obj) 以减少 sql 查询的数量。因为我正在序列化博客文章列表

Views.py

class BlogViewSet(ModelViewSet):
    queryset = Blog.objects.all().annotate(
        author_name=F('author__username')
    )
    serializer_class = BlogSerializer
    permission_classes = [IsOwnerOrReadOnly]

        def list(self, request):
            return Response({'blogs': BlogSerializer(self.queryset, many=True).data})

Serializers.py

class BlogSerializer(ModelSerializer):
    author_name = serializers.CharField(read_only=True)
    comments = SerializerMethodField()

    class Meta:
        model = Blog
        fields = ('title_text', 'main_text', 'datepublished', 'author_name', 'id', 'comments')


    def get_comments(self, obj):
        # filter comment
        comment_object = Comment.objects.filter(post_id=obj.id)
        comments = CommentSerializer(comment_object, many=True).data
        return comments

Answer 1

您不必从视图中传递任何内容。

• 首先，您必须更改 BlogSerializer 中的 comments 字段。

class CommentSerializer(ModelSerializer):
    # This serializer should have all the details of your comments.
    ....
    class Meta:
        model = Comment
        fields = "__all__" # Or whatever fields you want to set.

class BlogSerializer(ModelSerializer):
    author_name = serializers.CharField(read_only=True)
    comments = CommentSerializer(many=True, read_only=True) # I am not sure of the source of your comment reverse manager name

    class Meta:
        model = Blog
        fields = ('title_text', 'main_text', 'datepublished', 'author_name', 'id', 'comments')

• 其次，您必须对视图的查询集进行少量更改，以减少使用prefetch_related 发送到数据库的查询数量

class BlogViewSet(ModelViewSet):
    queryset = Blog.objects.prefetch_related('comments').all().annotate(
        author_name=F('author__username')
    )
    serializer_class = BlogSerializer
    permission_classes = [IsOwnerOrReadOnly]

        def list(self, request):
            return Response({'blogs': BlogSerializer(self.get_queryset(), many=True).data})

我在代码 sn-ps 中假设您没有为 Comment 模型在 Blog ForeignKey 上设置 related_name，因此默认情况下，Blog 上的相关管理器将是 @ 987654332@

更新

你的模型应该是这样的，为了让这个解决方案起作用

class Comment(models.Model):
    ...
    blog = models.ForeignKey('Blog', on_delete=models.CASCADE, related_name='comments')
    ...

class Blog(models.Model):
    # comment = models.ForeignKey(Comment, on_delete=models.CASCADE, null=True) 
    # this foreign key shouldn't be here, remove it.

    ....

对 Serializer 和 View 进行更改

# in BlogSerializer
    comments = CommentSerializer(many=True, read_only=True)
# In BlogViewSet
    queryset = Blog.objects.prefetch_related('comments').all().annotate(
        author_name=F('author__username')
    )