Django REST Polymorphic

Polymorphic serializers for Django REST Framework.

Overview

django-rest-polymorphic allows you to easily define serializers for your inherited models that you have created using django-polymorphic library.

Installation

Install using pip:

$ pip install django-rest-polymorphic

Usage

Define your polymorphic models:

# models.py
from django.db import models
from polymorphic.models import PolymorphicModel


class Project(PolymorphicModel):
    topic = models.CharField(max_length=30)


class ArtProject(Project):
    artist = models.CharField(max_length=30)


class ResearchProject(Project):
    supervisor = models.CharField(max_length=30)

Define serializers for each polymorphic model the way you did it when you used django-rest-framework:

# serializers.py
from rest_framework import serializers
from .models import Project, ArtProject, ResearchProject


class ProjectSerializer(serializers.ModelSerializer):
    class Meta:
        model = Project
        fields = ('topic', )


class ArtProjectSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = ArtProject
        fields = ('topic', 'artist', 'url')
        extra_kwargs = {
            'url': {'view_name': 'project-detail', 'lookup_field': 'pk'},
        }


class ResearchProjectSerializer(serializers.ModelSerializer):
    class Meta:
        model = ResearchProject
        fields = ('topic', 'supervisor')

Note that if you extend HyperlinkedModelSerializer instead of ModelSerializer you need to define extra_kwargs to direct the URL to the appropriate view for your polymorphic serializer.

Then you have to create a polymorphic serializer that serves as a mapper between models and serializers which you have defined above:

# serializers.py
from rest_polymorphic.serializers import PolymorphicSerializer


class ProjectPolymorphicSerializer(PolymorphicSerializer):
    model_serializer_mapping = {
        Project: ProjectSerializer,
        ArtProject: ArtProjectSerializer,
        ResearchProject: ResearchProjectSerializer
    }

Create viewset with serializer_class equals to your polymorphic serializer:

# views.py
from rest_framework import viewsets
from .models import Project
from .serializers import ProjectPolymorphicSerializer


class ProjectViewSet(viewsets.ModelViewSet):
    queryset = Project.objects.all()
    serializer_class = ProjectPolymorphicSerializer

Test it:

$ http GET "http://localhost:8000/projects/"

HTTP/1.0 200 OK
Content-Length: 227
Content-Type: application/json

[
    {
        "resourcetype": "Project",
        "topic": "John's gathering"
    },
    {
        "artist": "T. Turner",
        "resourcetype": "ArtProject",
        "topic": "Sculpting with Tim",
        "url": "http://localhost:8000/projects/2/"
    },
    {
        "resourcetype": "ResearchProject",
        "supervisor": "Dr. Winter",
        "topic": "Swallow Aerodynamics"
    }
]

$ http POST "http://localhost:8000/projects/" resourcetype="ArtProject" topic="Guernica" artist="Picasso"

HTTP/1.0 201 Created
Content-Length: 67
Content-Type: application/json

{
    "artist": "Picasso",
    "resourcetype": "ArtProject",
    "topic": "Guernica",
    "url": "http://localhost:8000/projects/4/"
}

Customize resource type

As you can see from the example above, in order to specify the type of your polymorphic model, you need to send a request with resource type field. The value of resource type should be the name of the model.

If you want to change the resource type field name from resourcetype to something else, you should override resource_type_field_name attribute:

class ProjectPolymorphicSerializer(PolymorphicSerializer):
    resource_type_field_name = 'projecttype'
    ...

If you want to change the behavior of resource type, you should override to_resource_type method:

class ProjectPolymorphicSerializer(PolymorphicSerializer):
    ...

    def to_resource_type(self, model_or_instance):
        return model_or_instance._meta.object_name.lower()

Now, the request for creating new object will look like this:

$ http POST "http://localhost:8000/projects/" projecttype="artproject" topic="Guernica" artist="Picasso"