django-rest-framework + django-多态模型序列化

Question

我想知道是否有人有将 Django REST 框架与 django-polymorphic 相结合的 Pythonic 解决方案。

给定：

class GalleryItem(PolymorphicModel):
    gallery_item_field = models.CharField()

class Photo(GalleryItem):
    custom_photo_field = models.CharField()

class Video(GalleryItem):
    custom_image_field = models.CharField()

如果我想要 django-rest-framework 中所有 GalleryItem 的列表，它只会给我 GalleryItem（父模型）的字段，因此：id、gallery_item_field 和 polymorphic_ctype。那不是我想要的。如果是照片实例，我想要 custom_photo_field，如果是视频，我想要 custom_image_field。

Answer 1

这是一个通用且可重复使用的解决方案。这是一个通用的Serializer，但修改它以使用ModelSerializer 并不难。它也不处理父类的序列化（在我的例子中，我更多地将父类用作接口）。

from typing import Dict, Type

from rest_framework import serializers


class PolymorphicSerializer(serializers.Serializer):
    """
    Serializer to handle multiple subclasses of another class

    - For serialized dict representations, a 'type' key with the class name as
      the value is expected: ex. {'type': 'Decimal', ... }
    - This type information is used in tandem with get_serializer_map(...) to
      manage serializers for multiple subclasses
    """
    def get_serializer_map(self) -> Dict[str, Type[serializers.Serializer]]:
        """
        Return a dict to map class names to their respective serializer classes

        To be implemented by all PolymorphicSerializer subclasses
        """
        raise NotImplementedError

    def to_representation(self, obj):
        """
        Translate object to internal data representation

        Override to allow polymorphism
        """
        type_str = obj.__class__.__name__

        try:
            serializer = self.get_serializer_map()[type_str]
        except KeyError:
            raise ValueError(
                'Serializer for "{}" does not exist'.format(type_str),
            )

        data = serializer(obj, context=self.context).to_representation(obj)
        data['type'] = type_str
        return data

    def to_internal_value(self, data):
        """
        Validate data and initialize primitive types

        Override to allow polymorphism
        """
        try:
            type_str = data['type']
        except KeyError:
            raise serializers.ValidationError({
                'type': 'This field is required',
            })

        try:
            serializer = self.get_serializer_map()[type_str]
        except KeyError:
            raise serializers.ValidationError({
                'type': 'Serializer for "{}" does not exist'.format(type_str),
            })

        validated_data = serializer(context=self.context) \
            .to_internal_value(data)
        validated_data['type'] = type_str
        return validated_data

    def create(self, validated_data):
        """
        Translate validated data representation to object

        Override to allow polymorphism
        """
        serializer = self.get_serializer_map()[validated_data['type']]
        return serializer(context=self.context).create(validated_data)

并使用它：

class ParentClassSerializer(PolymorphicSerializer):
    """
    Serializer for ParentClass objects
    """
    def get_serializer_map(self) -> Dict[str, Type[serializers.Serializer]]:
        """
        Return serializer map
        """
        return {
            ChildClass1.__name__: ChildClass1Serializer,
            ChildClass2.__name__: ChildClass2Serializer,
        }

Answer 2

为了完成，我添加了to_internal_value() 实现，因为我在最近的项目中需要它。

如何判断类型

有可能区分不同的“类”很方便；为此，我将 type 属性添加到基本多态模型中：

class GalleryItem(PolymorphicModel):
    gallery_item_field = models.CharField()

    @property
    def type(self):
        return self.__class__.__name__

这允许将type 称为“字段”和“只读字段”。

type 将包含 python 类名。

向序列化器添加类型

您可以将type 添加到“字段”和“只读字段”中 （如果你想在所有子模型中使用它们，你需要在所有序列化器中指定类型字段）

class PhotoSerializer(serializers.ModelSerializer):
    class Meta:
        model = models.Photo

    fields = ( ..., 'type', )
    read_only_fields = ( ..., 'type', )


class VideoSerializer(serializers.ModelSerializer):
    class Meta:
        model = models.Video

    fields = ( ..., 'type', )
    read_only_fields = ( ..., 'type', )

class GalleryItemModuleSerializer(serializers.ModelSerializer):
    class Meta:
        model = models.GalleryItem

    fields = ( ..., 'type', )
    read_only_fields = ( ..., 'type', )

    def to_representation(self, obj):
        pass # see the other comment

    def to_internal_value(self, data):
    """
    Because GalleryItem is Polymorphic
    """
    if data.get('type') == "Photo":
        self.Meta.model = models.Photo
        return PhotoSerializer(context=self.context).to_internal_value(data)
    elif data.get('type') == "Video":
        self.Meta.model = models.Video
        return VideoSerializer(context=self.context).to_internal_value(data)

    self.Meta.model = models.GalleryItem
    return super(GalleryItemModuleSerializer, self).to_internal_value(data)

Answer 3

到目前为止，我只针对 GET 请求进行了测试，并且可行：

class PhotoSerializer(serializers.ModelSerializer):

    class Meta:
        model = models.Photo


class VideoSerializer(serializers.ModelSerializer):

    class Meta:
        model = models.Video


class GalleryItemModuleSerializer(serializers.ModelSerializer):

    class Meta:
        model = models.GalleryItem

    def to_representation(self, obj):
        """
        Because GalleryItem is Polymorphic
        """
        if isinstance(obj, models.Photo):
            return PhotoSerializer(obj, context=self.context).to_representation(obj)
        elif isinstance(obj, models.Video):
           return VideoSerializer(obj, context=self.context).to_representation(obj)
        return super(GalleryItemModuleSerializer, self).to_representation(obj)

对于 POST 和 PUT 请求，您可能希望执行类似于使用 to_internal_value 定义覆盖 to_representation 定义的操作。