Django休息框架嵌套自引用对象

Question

我的模型看起来像这样:

class Category(models.Model):
    parentCategory = models.ForeignKey('self', blank=True, null=True, related_name='subcategories')
    name = models.CharField(max_length=200)
    description = models.CharField(max_length=500)

我设法用序列化器获得所有类别的平面json表示:

class CategorySerializer(serializers.HyperlinkedModelSerializer):
    parentCategory = serializers.PrimaryKeyRelatedField()
    subcategories = serializers.ManyRelatedField()

    class Meta:
        model = Category
        fields = ('parentCategory', 'name', 'description', 'subcategories')

现在我想要做的是子类别列表具有子类别的内联json表示而不是它们的ID.我怎么用django-rest-framework做到这一点？我试图在文档中找到它,但似乎不完整.

Answer 1

而不是使用ManyRelatedField,使用嵌套的序列化程序作为您的字段:

class SubCategorySerializer(serializers.ModelSerializer):
    class Meta:
        model = Category
        fields = ('name', 'description')

class CategorySerializer(serializers.ModelSerializer):
    parentCategory = serializers.PrimaryKeyRelatedField()
    subcategories = serializers.SubCategorySerializer()

    class Meta:
        model = Category
        fields = ('parentCategory', 'name', 'description', 'subcategories')

如果您想处理任意嵌套字段,您应该查看自定义文档的默认字段部分.您当前无法直接将序列化程序声明为字段,但您可以使用这些方法覆盖默认情况下使用的字段.

class CategorySerializer(serializers.ModelSerializer):
    parentCategory = serializers.PrimaryKeyRelatedField()

    class Meta:
        model = Category
        fields = ('parentCategory', 'name', 'description', 'subcategories')

        def get_related_field(self, model_field):
            # Handles initializing the `subcategories` field
            return CategorySerializer()

实际上,正如你所指出的,上述情况并不完全正确.这有点像黑客,但您可能会尝试在已经声明序列化程序后添加字段.

class CategorySerializer(serializers.ModelSerializer):
    parentCategory = serializers.PrimaryKeyRelatedField()

    class Meta:
        model = Category
        fields = ('parentCategory', 'name', 'description', 'subcategories')

CategorySerializer.base_fields['subcategories'] = CategorySerializer()

声明递归关系的机制是需要添加的.

编辑:请注意,现在有一个专门处理这种用例的第三方软件包.请参阅djangorestframework-recursive.

Answer 2

@ wjin的解决方案对我很有用,直到我升级到Django REST框架3.0.0,它弃用了tonative.这是我的DRF 3.0解决方案,稍作修改.

假设您有一个带有自引用字段的模型,例如名为"replies"的属性中的线程注释.您有此注释线程的树表示,并且您希望序列化树

首先,定义可重用的RecursiveField类

class RecursiveField(serializers.Serializer):
    def to_representation(self, value):
        serializer = self.parent.parent.__class__(value, context=self.context)
        return serializer.data

然后,对于序列化程序,使用RecursiveField序列化"回复"的值

class CommentSerializer(serializers.Serializer):
    replies = RecursiveField(many=True)

    class Meta:
        model = Comment
        fields = ('replies, ....)

简单易用,您只需要4行代码即可实现可重复使用的解决方案.

注意:如果你的数据结构比树更复杂,比如说有 向无环图(FANCY!)那么你可以试试@ wjin的包 - 看看他的解决方案.但是我对基于MPTTModel的树的解决方案没有任何问题.

Answer 3

在这里比赛的后期,但这是我的解决方案.假设我正在序列化一个Blah,还有多个Blah类型的孩子.

    class RecursiveField(serializers.Serializer):
        def to_native(self, value):
            return self.parent.to_native(value)

使用此字段,我可以序列化具有许多子对象的递归定义对象

    class BlahSerializer(serializers.Serializer):
        name = serializers.Field()
        child_blahs = RecursiveField(many=True)

我为DRF3.0编写了一个递归字段,并将其打包为pip https://pypi.python.org/pypi/djangorestframework-recursive/

Answer 4

另一个适用于Django REST Framework 3.3.2的选项:

class CategorySerializer(serializers.ModelSerializer):
    class Meta:
        model = Category
        fields = ('id', 'name', 'parentid', 'subcategories')

    def get_fields(self):
        fields = super(CategorySerializer, self).get_fields()
        fields['subcategories'] = CategorySerializer(many=True)
        return fields

Answer 5

另一种选择是在序列化模型的视图中进行递归.这是一个例子:

class DepartmentSerializer(ModelSerializer):
    class Meta:
        model = models.Department


class DepartmentViewSet(ModelViewSet):
    model = models.Department
    serializer_class = DepartmentSerializer

    def serialize_tree(self, queryset):
        for obj in queryset:
            data = self.get_serializer(obj).data
            data['children'] = self.serialize_tree(obj.children.all())
            yield data

    def list(self, request):
        queryset = self.get_queryset().filter(level=0)
        data = self.serialize_tree(queryset)
        return Response(data)

    def retrieve(self, request, pk=None):
        self.object = self.get_object()
        data = self.serialize_tree([self.object])
        return Response(data)

Answer 6

我能够用a实现这个结果serializers.SerializerMethodField.我不确定这是不是最好的方式,但对我有用:

class CategorySerializer(serializers.ModelSerializer):

    subcategories = serializers.SerializerMethodField(
        read_only=True, method_name="get_child_categories")

    class Meta:
        model = Category
        fields = [
            'name',
            'category_id',
            'subcategories',
        ]

    def get_child_categories(self, obj):
        """ self referral field """
        serializer = CategorySerializer(
            instance=obj.subcategories_set.all(),
            many=True
        )
        return serializer.data

Answer 7

我最近遇到了同样的问题,并提出了迄今为止似乎有效的解决方案,即使是任意深度.解决方案是Tom Christie的一个小修改:

class CategorySerializer(serializers.ModelSerializer):
    parentCategory = serializers.PrimaryKeyRelatedField()

    def convert_object(self, obj):
        #Add any self-referencing fields here (if not already done)
        if not self.fields.has_key('subcategories'):
            self.fields['subcategories'] = CategorySerializer()      
        return super(CategorySerializer,self).convert_object(obj) 

    class Meta:
        model = Category
        #do NOT include self-referencing fields here
        #fields = ('parentCategory', 'name', 'description', 'subcategories')
        fields = ('parentCategory', 'name', 'description')
#This is not needed
#CategorySerializer.base_fields['subcategories'] = CategorySerializer()

我不确定它在任何情况下都能可靠地工作,不过......

Answer 8

该解决方案与此处发布的其他解决方案几乎相似，但在根级别的子重复问题方面略有不同（如果您认为这是一个问题）。举个例子

class RecursiveSerializer(serializers.Serializer):
    def to_representation(self, value):
        serializer = self.parent.parent.__class__(value, context=self.context)
        return serializer.data

class CategoryListSerializer(ModelSerializer):
    sub_category = RecursiveSerializer(many=True, read_only=True)

    class Meta:
        model = Category
        fields = (
            'name',
            'slug',
            'parent', 
            'sub_category'
    )

如果你有这个观点

class CategoryListAPIView(ListAPIView):
    queryset = Category.objects.all()
    serializer_class = CategoryListSerializer

这将产生以下结果，

[
{
    "name": "parent category",
    "slug": "parent-category",
    "parent": null,
    "sub_category": [
        {
            "name": "child category",
            "slug": "child-category",
            "parent": 20,  
            "sub_category": []
        }
    ]
},
{
    "name": "child category",
    "slug": "child-category",
    "parent": 20,
    "sub_category": []
}
]

这里parent category有一个child categoryjson 表示正是我们想要它表示的。

child category但您可以看到在根级别有重复。

正如有些人在上面发布的答案的评论部分中询问的那样，我们如何才能在根级别停止这种子重复，只需使用 过滤您的查询集parent=None，如下所示

class CategoryListAPIView(ListAPIView):
    queryset = Category.objects.filter(parent=None)
    serializer_class = CategoryListSerializer

它会解决问题。

注意：这个答案可能与问题没有直接关系，但问题在某种程度上是相关的。而且这种使用方法RecursiveSerializer是昂贵的。如果您使用其他有性能倾向的选项会更好。

Answer 9

这是适用于drf 3.0.5和django 2.7.4的caipirginka解决方案的改编:

class CategorySerializer(serializers.ModelSerializer):

    def to_representation(self, obj):
        #Add any self-referencing fields here (if not already done)
        if 'branches' not in self.fields:
            self.fields['subcategories'] = CategorySerializer(obj, many=True)      
        return super(CategorySerializer, self).to_representation(obj) 

    class Meta:
        model = Category
        fields = ('id', 'description', 'parentCategory')

请注意,使用object和many = True属性调用第6行中的CategorySerializer.

Answer 10

我以为我会参加这个有趣的活动!

通过wjin和Mark Chackerian,我创建了一个更通用的解决方案,它适用于具有直通模型的直接树状模型和树结构.我不确定这是否属于它自己的答案,但我想我不妨把它放在某个地方.我包含了一个max_depth选项,它可以防止无限递归,在最深层次上,子节点被表示为URLS(如果你不想它是一个url,那就是最后的else子句).

from rest_framework.reverse import reverse
from rest_framework import serializers

class RecursiveField(serializers.Serializer):
    """
    Can be used as a field within another serializer,
    to produce nested-recursive relationships. Works with
    through models, and limited and/or arbitrarily deep trees.
    """
    def __init__(self, **kwargs):
        self._recurse_through = kwargs.pop('through_serializer', None)
        self._recurse_max = kwargs.pop('max_depth', None)
        self._recurse_view = kwargs.pop('reverse_name', None)
        self._recurse_attr = kwargs.pop('reverse_attr', None)
        self._recurse_many = kwargs.pop('many', False)

        super(RecursiveField, self).__init__(**kwargs)

    def to_representation(self, value):
        parent = self.parent
        if isinstance(parent, serializers.ListSerializer):
            parent = parent.parent

        lvl = getattr(parent, '_recurse_lvl', 1)
        max_lvl = self._recurse_max or getattr(parent, '_recurse_max', None)

        # Defined within RecursiveField(through_serializer=A)
        serializer_class = self._recurse_through
        is_through = has_through = True

        # Informed by previous serializer (for through m2m)
        if not serializer_class:
            is_through = False
            serializer_class = getattr(parent, '_recurse_next', None)

        # Introspected for cases without through models.
        if not serializer_class:
            has_through = False
            serializer_class = parent.__class__

        if is_through or not max_lvl or lvl <= max_lvl: 
            serializer = serializer_class(
                value, many=self._recurse_many, context=self.context)

            # Propagate hereditary attributes.
            serializer._recurse_lvl = lvl + is_through or not has_through
            serializer._recurse_max = max_lvl

            if is_through:
                # Delay using parent serializer till next lvl.
                serializer._recurse_next = parent.__class__

            return serializer.data
        else:
            view = self._recurse_view or self.context['request'].resolver_match.url_name
            attr = self._recurse_attr or 'id'
            return reverse(view, args=[getattr(value, attr)],
                           request=self.context['request'])