Django

Question

我有以下简单的 models.py 文件：

from django.db import models
from model_utils.managers import InheritanceManager

class Clique(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    name = models.CharField(max_length=100, blank=False)

class Post(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    headline = models.TextField()
    clique = models.ForeignKey(Clique,
                               on_delete=models.CASCADE,
                               blank=True,
                               null=True)
    objects = InheritanceManager()
    def __str__(self):
        return self.headline


class VideoPost(Post):
    video = models.BooleanField(default=True)


class ImagePost(Post):
    image = models.BooleanField(default=True)

所以，有一个 Clique 模型可以包含多个 Post 实例。 Post 个实例可以是 ImagePost 或 VideoPost。因此，ImagePost和VideoPost都继承了Post.

现在，假设我要检索 ImagePost 子类实例。所以，我的 views.py 文件中有以下视图：

class PostList(generics.ListAPIView):
    serializer_class = PostSerializer

    def get_queryset(self):
        return Post.objects.select_subclasses(ImagePost)

当我在 url 中传递端点 posts/ 时，将触发此视图，它应该只给我 ImagePost 个实例，对吗？但我也从数据库中获取了 VideoPost 个实例：

[
    {
        "clique": "http://127.0.0.1:8000/cliques/1/", 
        "comment_set": [], 
        "created": "2019-06-18T09:52:47.929623Z", 
        "headline": "FirstImagePost", 
        "id": 1, 
        "url": "http://127.0.0.1:8000/posts/1/"
    }, 
    {
        "clique": "http://127.0.0.1:8000/cliques/1/", 
        "comment_set": [], 
        "created": "2019-06-18T09:53:20.266653Z", 
        "headline": "FirstVideoPost", 
        "id": 2, 
        "url": "http://127.0.0.1:8000/posts/2/"
    }
]

为什么会这样？我浏览了官方文档 here 。有人可以帮忙

为了完整起见，我的 serializers.py 文件如下所示：

from rest_framework import serializers
from posts.models import Post, VideoPost, ImagePost, Clique

class CliqueSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Clique
        fields = ('id', 'name', 'post_set')
        read_only_fields = ('post_set', )

class PostSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Post
        fields = ('url', 'id', 'created', 'headline', 'clique', 'comment_set',)
        read_only_fields = ('comment_set',)


class VideoPostSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = VideoPost
        fields = '__all__'


class ImagePostSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = ImagePost
        fields = '__all__'

Answer 1

从文档来看，select_subclasses 似乎没有为您按子类类型进行过滤，它仅在与您提供的内容匹配时才将其转换为子类。

你的情况

Post.objects.select_subclasses(ImagePost)

会将所有 ImagePost 转换为 ImagePost 实例，将其他实例保留为 Post 对象，它不会将其过滤掉。

来自此处的文档：

nearby_places = Place.objects.select_subclasses("restaurant")
# restaurants will be Restaurant instances, bars will still be Place instances

在你的情况下你可以简单地做：

Post.objects.filter(imagepost__image=True).select_subclasses(ImagePost)

虽然我认为你不需要select_subclasses(ImagePost)部分

Django - InheritanceManager 不工作

Django - InheritanceManager is not working

python

inheritance

subclass