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Quickstart
===========
Install the project using::
pip install django-polymorphic
Update the settings file::
INSTALLED_APPS += (
'polymorphic',
'django.contrib.contenttypes',
)
The current release of *django-polymorphic* supports Django 1.4, 1.5 and 1.6 and Python 3 is supported.
Making Your Models Polymorphic
------------------------------
Use ``PolymorphicModel`` instead of Django's ``models.Model``, like so::
from polymorphic 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`` or ``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: When using the ``dumpdata`` management command on polymorphic tables
(or any table that has a reference to :class:`~django.contrib.contenttypes.models.ContentType`),
include the ``--natural`` flag in the arguments. This makes sure the
:class:`~django.contrib.contenttypes.models.ContentType` models will be referenced by name
instead of their primary key as that changes between Django instances.
.. 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!
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