Django rest framework nested self-referential objects

Solution 1:

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.

Solution 2:

@wjin's solution was working great for me until I upgraded to Django REST framework 3.0.0, which deprecates to_native. Here's my DRF 3.0 solution, which is a slight modification.

Say you have a model with a self-referential field, for example threaded comments in a property called "replies". You have a tree representation of this comment thread, and you want to serialize the tree

First, define your reusable RecursiveField class

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

Then, for your serializer, use the the RecursiveField to serialize the value of "replies"

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

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

Easy peasy, and you only need 4 lines of code for a re-usable solution.

NOTE: If your data structure is more complicated than a tree, like say a directed acyclic graph (FANCY!) then you could try @wjin's package -- see his solution. But I haven't had any problems with this solution for MPTTModel based trees.

Solution 3:

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

Solution 4:

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/