Django REST Polymorphic

Warnings

• breaking The core `PolymorphicSerializer` functionality has been incorporated directly into `django-polymorphic` (specifically at `polymorphic.contrib.drf.serializers.PolymorphicSerializer`). While `django-rest-polymorphic` still exists, the recommended approach for new projects or migrating existing ones is to switch imports.
  Fix: Change import statements from `from rest_polymorphic.serializers import PolymorphicSerializer` to `from polymorphic.contrib.drf.serializers import PolymorphicSerializer`.
• gotcha When extending `HyperlinkedModelSerializer` instead of `ModelSerializer`, you need to explicitly define `extra_kwargs` to direct the URL to the appropriate view for your polymorphic serializer. This ensures correct URL generation for specific child types.
  Fix: Add `extra_kwargs` to your child serializers' `Meta` class, for example: `extra_kwargs = {'url': {'view_name': 'drf:project-detail', 'lookup_field': 'pk'}}`.
• gotcha By default, the polymorphic type is identified by a field named `resource_type`. If you need to use a different field name in your API requests/responses, you must override the `resource_type_field_name` attribute.
  Fix: Set `resource_type_field_name = 'your_custom_type_field'` on your `PolymorphicSerializer` subclass.
• gotcha Using `django-polymorphic` (and consequently `django-rest-polymorphic`) for model inheritance can have performance implications. Each query to a base polymorphic model will result in `INNER JOIN` operations to fetch fields from subclassed models.
  Fix: Be mindful of performance for very deep inheritance hierarchies or extremely large datasets. Consider alternative inheritance strategies if performance becomes a critical bottleneck. Ensure appropriate database indexing.

Install

• pip install django-rest-polymorphic Install with pip

Imports

• PolymorphicSerializer

  from rest_polymorphic.serializers import PolymorphicSerializer

  While this was the original import for django-rest-polymorphic, the core functionality (PolymorphicSerializer) has been incorporated into django-polymorphic itself. The recommended import path for new projects or migrations is now `from polymorphic.contrib.drf.serializers import PolymorphicSerializer`.

Quickstart

This quickstart demonstrates how to set up polymorphic models using `django-polymorphic`, define individual `ModelSerializer`s for each concrete type, and then create a `PolymorphicSerializer` to handle the mapping. Finally, it shows how to integrate this into a Django REST Framework `ViewSet` to expose a polymorphic API endpoint. You would then include this ViewSet in your Django project's `urls.py`.

from django.db import models
from rest_framework import serializers, viewsets
from polymorphic.models import PolymorphicModel
from rest_polymorphic.serializers import PolymorphicSerializer

# 1. Define polymorphic models using django-polymorphic
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)

# 2. Define serializers for each concrete model
class ProjectSerializer(serializers.ModelSerializer):
    class Meta:
        model = Project
        fields = ('topic', 'resource_type') # 'resource_type' is added automatically by PolymorphicSerializer

class ArtProjectSerializer(serializers.ModelSerializer):
    class Meta:
        model = ArtProject
        fields = ('topic', 'artist', 'resource_type')

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

# 3. Create a PolymorphicSerializer to map models to serializers
class ProjectPolymorphicSerializer(PolymorphicSerializer):
    model_serializer_mapping = {
        Project: ProjectSerializer,
        ArtProject: ArtProjectSerializer,
        ResearchProject: ResearchProjectSerializer
    }

# 4. Use the polymorphic serializer in a ViewSet
class ProjectViewSet(viewsets.ModelViewSet):
    queryset = Project.objects.all()
    serializer_class = ProjectPolymorphicSerializer