两个字段的unique_together与read_only_fields混乱 [英] unique_together of two field messes with read_only_fields

问题描述

我具有用于评分课程的以下代码，应该从请求授权和URL中自动添加用户和课程：

I have this code for rating lessons, user and lesson should be added automatically from request authorization and URL:

＃views.py

class RatingViewSet(
    mixins.ListModelMixin,
    mixins.CreateModelMixin,
    viewsets.GenericViewSet
):
    permission_classes = [permissions.IsAuthenticated]
    serializer_class = RatingSerializer

    def perform_create(self, serializer):
        lessonInstance = Lesson.objects.get(id = self.kwargs['lessonID'])
        serializer.save(user=self.request.user, lesson = lessonInstance)
    def get_queryset(self):
        lessonID = self.kwargs['lessonID']
        return Rating.objects.filter(user=self.request.user, lesson=lessonID)

＃serializers.py

class RatingSerializer(serializers.ModelSerializer):
    class Meta:
        model = Rating
        fields = ('id', 'lesson','user', 'difficulty')
        read_only_fields = ('id', 'user','lesson')

＃models.py

class Rating(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL)
    lesson = models.ForeignKey('lessons.Lesson')
    difficulty = models.IntegerField()
    class meta:
        unique_together('user','lesson')

我希望每个用户/课程最多获得1个评分，因此 unique_together（'user'，'lesson'）。但是存在一个问题：只要代码中存在该约束，没有 user 或 lesson 字段的请求都会被拒绝带有必填字段的错误，即使它们是 read_only 。

I want to have max 1 rating per user/lesson, hence unique_together('user','lesson'). But there is a problem: as long as that constraint is in the code, requests without user or lesson fields get denied with field required error, even though they are read_only.

（如果我使用 unique_together（'user'，'lesson'）进行迁移，则删除该行即可，但是一旦出现该行，我就会报错。）

(If I migrate with unique_together('user','lesson'), then delete that line it works, but as soon as it's there I get errors.)

我想在那儿保留那段代码，所以我不会在以后的迁移中不小心删除 unique_together 约束。

I want to keep that bit of code there so I don't accidentally remove the unique_together constraint on later migrations.

推荐答案

这是特例，需要使用其他方法。这是 django-rest-framework 文档（请参见注释）说明这种情况：

This is a special-case that requires a different approach. Here's what django-rest-framework documentation (see the Note) says about this case:

正确的方法解决此问题的方法是在串行器
上显式指定字段，同时提供 read_only = True 和 default =…
关键字参数。

The right way to deal with this is to specify the field explicitly on the serializer, providing both the read_only=True and default=… keyword arguments.

在您的情况下，您需要明确定义用户 RatingSerializer 上的用户和课程字段，例如：

In your case, you need to explicitly define the user and lesson fields on your RatingSerializer, like this:

class RatingSerializer(serializers.ModelSerializer):
    user = serializers.PrimaryKeyRelatedField(read_only=True, default=serializers.CurrentUserDefault())  # gets the user from request
    lesson = serializers.PrimaryKeyRelatedField(read_only=True, default=None)  # or any other appropriate value

    class Meta:
        model = Rating
        fields = ('id', 'lesson','user', 'difficulty')

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