Quickstart

Install the project using:

pip install django-polymorphic

Update the settings file:

INSTALLED_APPS += (
    'polymorphic',
    'django.contrib.contenttypes',
)

Making Your Models Polymorphic

Use PolymorphicModel instead of Django’s Model, like so:

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)

All models inheriting from your polymorphic models will be polymorphic as well.

Using Polymorphic Models

Create some objects:

>>> Project.objects.create(topic="Department Party")
>>> ArtProject.objects.create(topic="Painting with Tim", artist="T. Turner")
>>> ResearchProject.objects.create(topic="Swallow Aerodynamics", supervisor="Dr. Winter")

Get polymorphic query results:

>>> Project.objects.all()
[ <Project:         id 1, topic "Department Party">,
  <ArtProject:      id 2, topic "Painting with Tim", artist "T. Turner">,
  <ResearchProject: id 3, topic "Swallow Aerodynamics", supervisor "Dr. Winter"> ]

Use instance_of() and not_instance_of() for narrowing the result to specific subtypes:

>>> Project.objects.instance_of(ArtProject)
[ <ArtProject:      id 2, topic "Painting with Tim", artist "T. Turner"> ]

>>> Project.objects.instance_of(ArtProject) | Project.objects.instance_of(ResearchProject)
[ <ArtProject:      id 2, topic "Painting with Tim", artist "T. Turner">,
  <ResearchProject: id 3, topic "Swallow Aerodynamics", supervisor "Dr. Winter"> ]

Polymorphic filtering: Get all projects where Mr. Turner is involved as an artist or supervisor (note the three underscores):

>>> Project.objects.filter(Q(ArtProject___artist='T. Turner') | Q(ResearchProject___supervisor='T. Turner'))
[ <ArtProject:      id 2, topic "Painting with Tim", artist "T. Turner">,
  <ResearchProject: id 4, topic "Color Use in Late Cubism", supervisor "T. Turner"> ]

This is basically all you need to know, as django-polymorphic mostly works fully automatic and just delivers the expected results.

Note

While django-polymorphic makes subclassed models easy to use in Django, we still encourage to use them with caution. Each subclassed model will require Django to perform an INNER JOIN to fetch the model fields from the database. While taking this in mind, there are valid reasons for using subclassed models. That’s what this library is designed for!