Django Rest Framework POST 和 GET 嵌套序列化程序

Question

我一直在为看板风格的项目板开发自己的 API。我附上了一张 UML 图来显示“板”应用程序是如何组织的。

My Application's Model UML Diagram

我的问题是，当我想创建一张新卡时，我希望能够通过在 POST 参数中传递的主键创建带有标签列表的卡，如下所示:

{
    "title": "Test Card",
    "description": "This is a Test Card!",
    "created_by": 1,
    "labels": [1,2]
}

我的另一个要求是我想检索序列化标签作为卡片对象的一部分，如下所示:

{
    "id": 1,
    "board": 1,
    "title": "Some Card",
    "description": "The description of Some Card.",
    "created_by": 1,
    "assignees": [
        {
            "id": 1,
            "username": "test1",
            "email": "test1_user@hotmail.co.uk"
        }
    ],
    "labels": [
        {
            "id": 1,
            "board": 1,
            "title": "Pink Label",
            "color": "#f442cb"
        }
    ],
    "comment_set": []
}

我将假设要实现 POST 和 GET 功能的这种差异，我将不得不拥有 2 个不同的序列化程序？

然而，这篇文章的主要问题与上面提到的 POST 数据的创建逻辑有关。我不断收到这样的错误:

{
    "labels": [
        {
            "non_field_errors": [
                "Invalid data. Expected a dictionary, but got int."
            ]
        },
        {
            "non_field_errors": [
                "Invalid data. Expected a dictionary, but got int."
            ]
        }
    ]
}

我在我的 CardSerializer 中尝试了许多不同的 DRF 序列化程序组合，但最终总是得到与上述格式相同的错误消息:“预期但得到”。任何帮助或指示，甚至有人告诉我这是糟糕的 REST 设计，例如，将不胜感激! :)

编辑:我应该补充一点，如果我将 CardSerializer 标签字段从 LabelSerializer 更改为 PrimaryKeyRelatedField (如代码中的注释所示)，我收到以下错误:

禁止直接分配给多对多集合的前端。改用labels.set()。

以下是我的源代码的相关部分:

模型.py

class Card(models.Model):
"""Represents a card."""

    # Parent
    board = models.ForeignKey(Board, on_delete=models.CASCADE)
    column = models.ForeignKey(Column, on_delete=models.CASCADE, null=True)

    # Fields
    title = models.CharField(max_length=255, null=False)
    description = models.TextField()

    assignees = models.ManyToManyField(User, blank=True, related_name='card_assignees')
    labels = models.ManyToManyField(Label, blank=True, related_name='card_labels')

    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(blank=True, null=True)  # Blank for django-admin

    created_by = models.ForeignKey(User, on_delete=models.CASCADE, related_name='card_created_by')

View .py

class CardList(generics.ListCreateAPIView):
    queryset = Card.objects.all()
    serializer_class = CardSerializer

    def get_queryset(self):
        columns = Column.objects.filter(board_id=self.kwargs['board_pk'])
        queryset = Card.objects.filter(column__in=columns)
        return queryset

    def post(self, request, *args, **kwargs):
        board = Board.objects.get(pk=kwargs['board_pk'])

        post_data = {
            'title': request.data.get('title'),
            'description': request.data.get('description'),
            'created_by': request.data.get('created_by'),
            'assignees': request.data.get('assignees'),
            'labels': request.data.get('labels'),
        }
        serializer = CardSerializer(data=post_data, context={'board': board})

        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status.HTTP_201_CREATED)
        return Response(serializer.errors, status.HTTP_400_BAD_REQUEST)

serializers.py

class UserSerializer(serializers.ModelSerializer):
    """Serializer to map the User instance to JSON."""

    class Meta:
        model = User
        fields = ('id', 'username', 'email')


class CommentSerializer(serializers.ModelSerializer):
    """Serializer to map the Comment instance to JSON."""

    class Meta:
        model = Comment
        fields = '__all__'


class LabelSerializer(serializers.ModelSerializer):
    """Serializer to map the Label instance to JSON."""

    class Meta:
        model = Label
        fields = ('id', 'board', 'title', 'color')


class CardSerializer(serializers.ModelSerializer):
    """Serializer to map the Card instance to JSON."""
    assignees = UserSerializer(many=True, read_only=True)
    labels = LabelSerializer(many=True)
    comment_set = CommentSerializer(many=True, read_only=True)

    # assignees = PrimaryKeyRelatedField(many=True, read_only=True)
    # labels = PrimaryKeyRelatedField(many=True, queryset=Label.objects.all())

    def create(self, validated_data):
        board = self.context['board']
        card = Card.objects.create(
            board=board,
            **validated_data
        )
        return card

    class Meta:
        model = Card
        fields = ('id', 'board', 'title', 'description', 'created_by', 'assignees', 'labels', 'comment_set')
        read_only_fields = ('id', 'board')

Answer 1

我设法找到了解决方案，但这可能不符合最佳实践。如果有人能澄清这一点，那就太好了。但是，就目前而言:

我将 CardSerializer 中的 create 函数更改为以下内容:

def create(self, validated_data):
    board = self.context['board']
    labels_data = validated_data.pop('labels')
    card = Card.objects.create(
        board=board,
        **validated_data
    )
    card.labels.set(labels_data)
    return card

card.labels.set(labels_data) 行表示我绕过以下错误消息:

Direct assignment to the forward side of a many-to-many set is prohibited.

这就是为什么我不确定这是否是“正确”的事情，但它现在似乎有效。