How to serialize hierarchical relationship in Django REST

Question

I have a Django model that is hierarchical using django-mptt, which looks like:

class UOMCategory(MPTTModel, BaseModel):
    """
        This represents categories of different unit of measurements.
    """
    name = models.CharField(max_length=50, unique=True)
    description = models.CharField(max_length=50, unique=True)
    parent = TreeForeignKey('self', null=True, blank=True, related_name='%(app_label)s_%(class)s_sub_uom_categories')

The problem now is I created a REST API using Django REST Framework; how do I make sure that parent field returns serialized data?

Here is the Model Serializer:

class UOMCategorySerializer(BaseModelSerializer):
    """
    REST API Serializer for UOMCategory model
    """
    class Meta:
        model = UOMCategory

Answer 1

In DRF you can use a serializer as a field in another serializer. However, recursion is not possible.

Tom Christie posted a solution on another question (Django rest framework nested self-referential objects). His solution will also work with your problem.

In your UOMCategorySerializer.Meta class you specify the fields you want to use, also list the parent and/or children field(s) there. Then you use Tom Christies solution.

In your case this would give:

class UOMCategorySerializer(ModelSerializer):
    class Meta:
        model = UOMCategory
        fields = ('name', 'description', 'parent', 'children')

Tom Christies solution: By specifying what field to use for parent and/or children, you avoid using too much (and possibily endless) recursion:

UOMCategorySerializer.base_fields['parent'] = UOMCategorySerializer()
UOMCategorySerializer.base_fields['children'] = UOMCategorySerializer(many=True)

The above works for me in a similar situation.

Answer 2

Simple DRF API view using MPTT cache and DRF serializer.

from rest_framework import serializers
from rest_framework.generics import GenericAPIView
from rest_framework.response import Response

from events.models import Category


class CategorySerializer(serializers.ModelSerializer):
    class Meta:
        model = Category
        fields = (
            "name",
            "slug",
        )


class CategoryTreeView(GenericAPIView):
    serializer_class = CategorySerializer

    def get(self, request, *args, **kwargs):
        root_nodes = Category.objects.all().get_cached_trees()

        data = []
        for n in root_nodes:
            data.append(self.recursive_node_to_dict(n))

        return Response(data)

    def recursive_node_to_dict(self, node):
        result = self.get_serializer(instance=node).data
        children = [self.recursive_node_to_dict(c) for c in node.get_children()]
        if children:
            result["children"] = children
        return result