[PYTHON] I want to create an API that returns a model with a recursive relationship in the Django REST Framework

Goal of this article

Consider the case of a model with recursive relations (such as a tree structure). Create an API that recursively returns json using Django REST Framework.

environment

MacOS(10.11.6 / ElCapitane) Python 3.5.2 Django 1.10.4 DjangoRESTFramework 3.5.3

Model

Defines a model with a recursive relationship. Consider a model that has more subcategories within the category. The reverse relation name is subcategories.

models.py

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)

Serializer Define SubCategorySerializer that inherits ModelSerializer, and overwrite subcategories, which is the inverse relation of Category, with SubCategorySerializer. At this time, parentCategory should return serializers.PrimaryKeyRelatedField ().

serializers.py

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')

View

It is OK if you specify CategorySerializer for Serializer in View. The query set should be a query that can uniquely retrieve the top hierarchy. If you use get (), you will get the object, so use filter () that returns a query. (For example, define is_root in the model and get it with filter (is_root = True))

view.py

class CategoryListViewSet(viewsets.ModelViewSet):
    queryset = Category.objects.filter(id='e.g...root_category_id').prefetch_related('subcategories__subcategories')
    serializer_class = CategorySeriarizer

Another way

It can also be realized by defining and returning the following RecursiveField. I think this is also good because it is flexible.

serializers.py

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

class CategorySerializer(serializers.Serializer):
    subcategories = RecursiveField(many=True)

    class Meta:
        model = Comment
        fields = ('parendCategory','name', 'description', 'subcategories')

result

It is a different model from the above example, but if it is a file system model with a simple tree structure and recursive relations, this json will be returned.

hoge.json

[
    {
        "name": "RootDirectory",
        "is_root": true,
        "is_dir": true,
        "parent_file": null,
        "child_files": [
            {
                "name": "root_file",
                "is_root": false,
                "is_dir": false,
                "parent_file": 34,
                "child_files": []
            },
            {
                "name": "TestDir",
                "is_root": false,
                "is_dir": true,
                "parent_file": 34,
                "child_files": [
                    {
                        "name": "test.zip",
                        "is_root": false,
                        "is_dir": false,
                        "parent_file": 35,
                        "child_files": []
                    },
                    {
                        "name": "test_dir_file.png ",
                        "is_root": false,
                        "is_dir": false,
                        "parent_file": 35,
                        "child_files": []
                    }
                ]
            }
        ]
    }
]

Let's all have fun with Django and create a REST API! !!

reference

http://www.django-rest-framework.org/api-guide/relations/#custom-relational-fields http://stackoverflow.com/questions/13376894/django-rest-framework-nested-self-referential-objects