Django rest framework nested self-referential obje

Question

I have model that looks like this:

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)

I managed to get flat json representation of all categories with serializer:

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

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

Now what I want to do is for subcategories list to have inline json representation of subcategories instead of their ids. How would I do that with django-rest-framework? I tried to find it in documentation, but it seems incomplete.

Answer 1

This is an adaptation from the caipirginka solution that works on drf 3.0.5 and django 2.7.4:

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')

Note that the CategorySerializer in 6th line is called with the object and the many=True attribute.

Answer 2

Instead of using ManyRelatedField, use a nested serializer as your field:

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')

If you want to deal with arbitrarily nested fields you should take a look at the customising the default fields part of the docs. You can't currently directly declare a serializer as a field on itself, but you can use these methods to override what fields are used by default.

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()

---

Actually, as you've noted the above isn't quite right. This is a bit of a hack, but you might try adding the field in after the serializer is already declared.

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

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

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

A mechanism of declaring recursive relationships is something that needs to be added.

---

Edit: Note that there is now a third-party package available that specifically deals with this kind of use-case. See djangorestframework-recursive.

Answer 3

Another option would be to recurse in the view that serializes your model. Here's an example:

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 4

I recently had the same problem and came up with a solution that seems to work so far, even for arbitrary depth. The solution is a small modification of the one from Tom Christie:

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()

I'm not sure it can reliably work in any situation, though...

Answer 5

Late to the game here, but here's my solution. Let's say I'm serializing a Blah, with multiple children also of type Blah.

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

Using this field I can serialize my recursively-defined objects that have many child-objects

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

---

I wrote a recursive field for DRF3.0 and packaged it for pip https://pypi.python.org/pypi/djangorestframework-recursive/

Answer 6

Another option that works with Django REST Framework 3.3.2:

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