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Port documentation to Sphinx, cleanup README

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Diederik van der Boor
2013-05-19 17:15:41 +02:00
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docs/Makefile
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# Makefile for Sphinx documentation
#
# You can set these variables from the command line.
SPHINXOPTS =
SPHINXBUILD = sphinx-build
PAPER =
BUILDDIR = _build
# Internal variables.
PAPEROPT_a4 = -D latex_paper_size=a4
PAPEROPT_letter = -D latex_paper_size=letter
ALLSPHINXOPTS = -d $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
# the i18n builder cannot share the environment and doctrees with the others
I18NSPHINXOPTS = $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
.PHONY: help clean html dirhtml singlehtml pickle json htmlhelp qthelp devhelp epub latex latexpdf text man changes linkcheck doctest gettext
help:
@echo "Please use \`make <target>' where <target> is one of"
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@echo
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@echo "# assistant -collectionFile $(BUILDDIR)/qthelp/django-polymorphic.qhc"
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@echo "# devhelp"
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docs/admin.rst
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Django admin integration
========================
Off course, it's possible to register individual polymorphic models in the Django admin interface.
However, to use these models in a single cohesive interface, some extra base classes are available.
The polymorphic admin interface works in a simple way:
* The add screen gains an additional step where the desired child model is selected.
* The edit screen displays the admin interface of the child model.
* The list screen still displays all objects of the base class.
The polymorphic admin is implemented via a parent admin that forwards the *edit* and *delete* views
to the ``ModelAdmin`` of the derived child model. The *list* page is still implemented by the parent model admin.
Both the parent model and child model need to have a ``ModelAdmin`` class.
Only the ``ModelAdmin`` class of the parent/base model has to be registered in the Django admin site.
The parent model
----------------
The parent model needs to inherit ``PolymorphicParentModelAdmin``, and implement the following:
* ``base_model`` should be set
* ``child_models`` or ``get_child_models()`` should return a list with (Model, ModelAdmin) tuple.
The exact implementation can depend on the way your module is structured.
For simple inheritance situations, ``child_models`` is the best solution.
For large applications, ``get_child_models()`` can be used to query a plugin registration system.
The child models
----------------
The admin interface of the derived models should inherit from ``PolymorphicChildModelAdmin``.
Again, ``base_model`` should be set in this class as well.
This class implements the following features:
* It corrects the breadcrumbs in the admin pages.
* It extends the template lookup paths, to look for both the parent model and child model in the ``admin/app/model/change_form.html`` path.
* It allows to set ``base_form`` so the derived class will automatically include other fields in the form.
* It allows to set ``base_fieldsets`` so the derived class will automatically display any extra fields.
The standard ``ModelAdmin`` attributes ``form`` and ``fieldsets`` should rather be avoided at the base class,
because it will hide any additional fields which are defined in the derived model. Instead,
use the ``base_form`` and ``base_fieldsets`` instead. The ``PolymorphicChildModelAdmin`` will
automatically detect the additional fields that the child model has, display those in a separate fieldset.
Example
-------
.. code-block:: python
from django.contrib import admin
from polymorphic.admin import PolymorphicParentModelAdmin, PolymorphicChildModelAdmin
class ModelAChildAdmin(PolymorphicChildModelAdmin):
""" Base admin class for all child models """
base_model = ModelA
# By using these `base_...` attributes instead of the regular ModelAdmin `form` and `fieldsets`,
# the additional fields of the child models are automatically added to the admin form.
base_form = ...
base_fieldsets = (
...
)
class ModelBAdmin(ModelAChildAdmin):
# define custom features here
class ModelCAdmin(ModelBAdmin):
# define custom features here
class ModelAParentAdmin(PolymorphicParentModelAdmin):
""" The parent model admin """
base_model = ModelA
child_models = (
(ModelB, ModelBAdmin),
(ModelC, ModelCAdmin),
)
# Only the parent needs to be registered:
admin.site.register(ModelA, ModelAParentAdmin)
docs/advanced.rst
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Advanced features
=================
In the examples below, these models are being used::
from polymorphic import PolymorphicModel
class ModelA(PolymorphicModel):
field1 = models.CharField(max_length=10)
class ModelB(ModelA):
field2 = models.CharField(max_length=10)
class ModelC(ModelB):
field3 = models.CharField(max_length=10)
Filtering for classes (equivalent to python's isinstance() ):
-------------------------------------------------------------
>>> ModelA.objects.instance_of(ModelB)
.
[ <ModelB: id 2, field1 (CharField), field2 (CharField)>,
<ModelC: id 3, field1 (CharField), field2 (CharField), field3 (CharField)> ]
In general, including or excluding parts of the inheritance tree::
ModelA.objects.instance_of(ModelB [, ModelC ...])
ModelA.objects.not_instance_of(ModelB [, ModelC ...])
You can also use this feature in Q-objects (with the same result as above):
>>> ModelA.objects.filter( Q(instance_of=ModelB) )
Polymorphic filtering (for fields in derived classes)
-----------------------------------------------------
For example, cherrypicking objects from multiple derived classes
anywhere in the inheritance tree, using Q objects (with the
syntax: ``exact model name + three _ + field name``):
>>> ModelA.objects.filter( Q(ModelB___field2 = 'B2') | Q(ModelC___field3 = 'C3') )
.
[ <ModelB: id 2, field1 (CharField), field2 (CharField)>,
<ModelC: id 3, field1 (CharField), field2 (CharField), field3 (CharField)> ]
Combining Querysets
-------------------
Querysets could now be regarded as object containers that allow the
aggregation of different object types, very similar to python
lists - as long as the objects are accessed through the manager of
a common base class:
>>> Base.objects.instance_of(ModelX) | Base.objects.instance_of(ModelY)
.
[ <ModelX: id 1, field_x (CharField)>,
<ModelY: id 2, field_y (CharField)> ]
ManyToManyField, ForeignKey, OneToOneField
------------------------------------------
Relationship fields referring to polymorphic models work as
expected: like polymorphic querysets they now always return the
referred objects with the same type/class these were created and
saved as.
E.g., if in your model you define::
field1 = OneToOneField(ModelA)
then field1 may now also refer to objects of type ``ModelB`` or ``ModelC``.
A ManyToManyField example::
# The model holding the relation may be any kind of model, polymorphic or not
class RelatingModel(models.Model):
many2many = models.ManyToManyField('ModelA') # ManyToMany relation to a polymorphic model
>>> o=RelatingModel.objects.create()
>>> o.many2many.add(ModelA.objects.get(id=1))
>>> o.many2many.add(ModelB.objects.get(id=2))
>>> o.many2many.add(ModelC.objects.get(id=3))
>>> o.many2many.all()
[ <ModelA: id 1, field1 (CharField)>,
<ModelB: id 2, field1 (CharField), field2 (CharField)>,
<ModelC: id 3, field1 (CharField), field2 (CharField), field3 (CharField)> ]
Using Third Party Models (without modifying them)
-------------------------------------------------
Third party models can be used as polymorphic models without
restrictions by subclassing them. E.g. using a third party
model as the root of a polymorphic inheritance tree::
from thirdparty import ThirdPartyModel
class MyThirdPartyBaseModel(PolymorhpicModel, ThirdPartyModel):
pass # or add fields
Or instead integrating the third party model anywhere into an
existing polymorphic inheritance tree::
class MyBaseModel(SomePolymorphicModel):
my_field = models.CharField(max_length=10)
class MyModelWithThirdParty(MyBaseModel, ThirdPartyModel):
pass # or add fields
Non-Polymorphic Queries
-----------------------
If you insert ``.non_polymorphic()`` anywhere into the query chain, then
django_polymorphic will simply leave out the final step of retrieving the
real objects, and the manager/queryset will return objects of the type of
the base class you used for the query, like vanilla Django would
(``ModelA`` in this example).
>>> qs=ModelA.objects.non_polymorphic().all()
>>> qs
[ <ModelA: id 1, field1 (CharField)>,
<ModelA: id 2, field1 (CharField)>,
<ModelA: id 3, field1 (CharField)> ]
There are no other changes in the behaviour of the queryset. For example,
enhancements for ``filter()`` or ``instance_of()`` etc. still work as expected.
If you do the final step yourself, you get the usual polymorphic result:
>>> ModelA.objects.get_real_instances(qs)
[ <ModelA: id 1, field1 (CharField)>,
<ModelB: id 2, field1 (CharField), field2 (CharField)>,
<ModelC: id 3, field1 (CharField), field2 (CharField), field3 (CharField)> ]
About Queryset Methods
----------------------
* ``annotate()`` and ``aggregate()`` work just as usual, with the
addition that the ``ModelX___field`` syntax can be used for the
keyword arguments (but not for the non-keyword arguments).
* ``order_by()`` similarly supports the ``ModelX___field`` syntax
for specifying ordering through a field in a submodel.
* ``distinct()`` works as expected. It only regards the fields of
the base class, but this should never make a difference.
* ``select_related()`` works just as usual, but it can not (yet) be used
to select relations in derived models
(like ``ModelA.objects.select_related('ModelC___fieldxy')`` )
* ``extra()`` works as expected (it returns polymorphic results) but
currently has one restriction: The resulting objects are required to have
a unique primary key within the result set - otherwise an error is thrown
(this case could be made to work, however it may be mostly unneeded)..
The keyword-argument "polymorphic" is no longer supported.
You can get back the old non-polymorphic behaviour
by using ``ModelA.objects.non_polymorphic().extra(...)``.
* ``get_real_instances()`` allows you to turn a
queryset or list of base model objects efficiently into the real objects.
For example, you could do ``base_objects_queryset=ModelA.extra(...).non_polymorphic()``
and then call ``real_objects=base_objects_queryset.get_real_instances()``. Or alternatively
.``real_objects=ModelA.objects.get_real_instances(base_objects_queryset_or_object_list)``
* ``values()`` & ``values_list()`` currently do not return polymorphic
results. This may change in the future however. If you want to use these
methods now, it's best if you use ``Model.base_objects.values...`` as
this is guaranteed to not change.
* ``defer()`` and ``only()`` are not yet supported (support will be added
in the future).
Using enhanced Q-objects in any Places
--------------------------------------
The queryset enhancements (e.g. ``instance_of``) only work as arguments
to the member functions of a polymorphic queryset. Occationally it may
be useful to be able to use Q objects with these enhancements in other places.
As Django doesn't understand these enhanced Q objects, you need to
transform them manually into normal Q objects before you can feed them
to a Django queryset or function::
normal_q_object = ModelA.translate_polymorphic_Q_object( Q(instance_of=Model2B) )
This function cannot be used at model creation time however (in models.py),
as it may need to access the ContentTypes database table.
Nicely Displaying Polymorphic Querysets
---------------------------------------
In order to get the output as seen in all examples here, you need to use the
:class:`~polymorphic.showfields.ShowFieldType` class mixin::
from polymorphic import PolymorphicModel, ShowFieldType
class ModelA(ShowFieldType, PolymorphicModel):
field1 = models.CharField(max_length=10)
You may also use :class:`~polymorphic.showfields.ShowFieldContent`
or :class:`~polymorphic.showfields.ShowFieldTypeAndContent` to display
additional information when printing querysets (or converting them to text).
When showing field contents, they will be truncated to 20 characters. You can
modify this behaviour by setting a class variable in your model like this::
class ModelA(ShowFieldType, PolymorphicModel):
polymorphic_showfield_max_field_width = 20
...
Similarly, pre-V1.0 output formatting can be re-estated by using
``polymorphic_showfield_old_format = True``.
.. _restrictions:
Restrictions & Caveats
----------------------
* Database Performance regarding concrete Model inheritance in general.
Please see the :ref:`performance`.
* Queryset methods ``values()``, ``values_list()``, ``select_related()``,
``defer()`` and ``only()`` are not yet fully supported (see above).
``extra()`` has one restriction: the resulting objects are required to have
a unique primary key within the result set.
* Diamond shaped inheritance: There seems to be a general problem
with diamond shaped multiple model inheritance with Django models
(tested with V1.1 - V1.3).
An example is here: http://code.djangoproject.com/ticket/10808.
This problem is aggravated when trying to enhance models.Model
by subclassing it instead of modifying Django core (as we do here
with PolymorphicModel).
* The enhanced filter-definitions/Q-objects only work as arguments
for the methods of the polymorphic querysets. Please see above
for ``translate_polymorphic_Q_object``.
* 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.
.. old links:
- http://code.djangoproject.com/wiki/ModelInheritance
- http://lazypython.blogspot.com/2009/02/second-look-at-inheritance-and.html
- http://www.djangosnippets.org/snippets/1031/
- http://www.djangosnippets.org/snippets/1034/
- http://groups.google.com/group/django-developers/browse_frm/thread/7d40ad373ebfa912/a20fabc661b7035d?lnk=gst&q=model+inheritance+CORBA#a20fabc661b7035d
- http://groups.google.com/group/django-developers/browse_thread/thread/9bc2aaec0796f4e0/0b92971ffc0aa6f8?lnk=gst&q=inheritance#0b92971ffc0aa6f8
- http://groups.google.com/group/django-developers/browse_thread/thread/3947c594100c4adb/d8c0af3dacad412d?lnk=gst&q=inheritance#d8c0af3dacad412d
- http://groups.google.com/group/django-users/browse_thread/thread/52f72cffebb705e/b76c9d8c89a5574f
- http://peterbraden.co.uk/article/django-inheritance
- http://www.hopelessgeek.com/2009/11/25/a-hack-for-multi-table-inheritance-in-django
- http://stackoverflow.com/questions/929029/how-do-i-access-the-child-classes-of-an-object-in-django-without-knowing-the-name/929982#929982
- http://stackoverflow.com/questions/1581024/django-inheritance-how-to-have-one-method-for-all-subclasses
- http://groups.google.com/group/django-users/browse_thread/thread/cbdaf2273781ccab/e676a537d735d9ef?lnk=gst&q=polymorphic#e676a537d735d9ef
- http://groups.google.com/group/django-users/browse_thread/thread/52f72cffebb705e/bc18c18b2e83881e?lnk=gst&q=model+inheritance#bc18c18b2e83881e
- http://code.djangoproject.com/ticket/10808
- http://code.djangoproject.com/ticket/7270
docs/changelog.rst
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Changelog
==========
Version 0.4.2 (2013-04-10)
--------------------------
* Used proper ``__version__`` marker.
Version 0.4.1 (2013-04-10)
--------------------------
* Add Django 1.5 and 1.6 support
* Add proxy model support
* Add default admin ``list_filter`` for polymorphic model type.
* Fix queryset support of related objects.
* Performed an overall cleanup of the project
* **Deprecated** the ``queryset_class`` argument of the ``PolymorphicManager`` constructor, use the class attribute instead.
* **Dropped** Django 1.1, 1.2 and 1.3 support
Version 0.4 (2013-03-25)
------------------------
* Update example project for Django 1.4
* Added tox and Travis configuration
Version 0.3.1 (2013-02-28)
--------------------------
* SQL optimization, avoid query in pre_save_polymorphic()
Version 0.3 (2013-02-28)
------------------------
Many changes to the codebase happened, but no new version was released to pypi for years.
0.3 contains fixes submitted by many contributors, huge thanks to everyone!
* Added a polymorphic admin interface.
* PEP8 and code cleanups by various authors
Version 0.2 (2012-11-12)
------------------------
The 0.2 release serves as legacy release.
It supports Django 1.1 up till 1.4 and Python 2.4 up till 2.7.
For a detailed list of it's changes, see the :doc:`archived changelog <changelog_archive>`.
docs/changelog_archive.rst
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Archive of old changelog entries
================================
2011-01-24 V1.0 Release Candidate 1
------------------------------------
* Fixed GitHub issue 15 (query result incomplete with inheritance).
Thanks to John Debs for reporting and the test case.
2011-12-20 Renaming, refactoring, new maintainer
------------------------------------------------
Since the original author disappeared from the internet, we undertook to
maintain and upgrade this piece of software.
The latest "legacy" tag should be V1.0-RC-1. Anything above that should be
considered experimental and unstable until further notice (there be dragons).
New features, bug fixes and other improvements will be added to trunk from now on.
2010-11-11 V1.0 Beta 2
-----------------------
Beta 2 accumulated somewhat more changes than intended, and also
has been delayed by DBMS benchmark testing I wanted to do on model
inheritance. These benchmarks show that there are considerable
problems with concrete model inheritance and contemporary DBM systems.
The results will be forthcoming on the google discussion forum.
Please also see: http://www.jacobian.org/writing/concrete-inheritance/
The API should be stable now with Beta 2, so it's just about potential
bugfixes from now on regarding V1.0.
Beta 2 is still intended for testing and development environments and not
for production. No complaints have been heard regarding Beta 1 however,
and Beta 1 is used on a few production sites by some enterprising users.
There will be a release candidate for V1.0 in the very near future.
New Features and changes
~~~~~~~~~~~~~~~~~~~~~~~~
* API CHANGE: ``.extra()`` has been re-implemented. Now it's polymorphic by
default and works (nearly) without restrictions (please see docs). This is a (very)
incompatible API change regarding previous versions of django_polymorphic.
Support for the ``polymorphic`` keyword parameter has been removed.
You can get back the non-polymorphic behaviour by using
``ModelA.objects.non_polymorphic().extra(...)``.
* API CHANGE: ``ShowFieldContent`` and ``ShowFieldTypeAndContent`` now
use a slightly different output format. If this causes too much trouble for
your test cases, you can get the old behaviour back (mostly) by adding
``polymorphic_showfield_old_format = True`` to your model definitions.
``ShowField...`` now also produces more informative output for custom
primary keys.
* ``.non_polymorphic()`` queryset member function added. This is preferable to
using ``.base_objects...``, as it just makes the resulting queryset non-polymorphic
and does not change anything else in the behaviour of the manager used (while
``.base_objects`` is just a different manager).
* ``.get_real_instances()``: implementation modified to allow the following
more simple and intuitive use::
>>> qs = ModelA.objects.all().non_polymorphic()
>>> qs.get_real_instances()
which is equivalent to::
>>> ModelA.objects.all()
* added member function:
``normal_q_object = ModelA.translate_polymorphic_Q_object(enhanced_q_object)``
* misc changes/improvements
Bugfixes
~~~~~~~~
* Custom fields could cause problems when used as the primary key.
In derived models, Django's automatic ".pk" field does not always work
correctly for such custom fields: "some_object.pk" and "some_object.id"
return different results (which they shouldn't, as pk should always be just
an alias for the primary key field). It's unclear yet if the problem lies in
Django or the affected custom fields. Regardless, the problem resulting
from this has been fixed with a small workaround.
"python manage.py test polymorphic" also tests and reports on this problem now.
Thanks to Mathieu Steele for reporting and the test case.
2010-10-18 V1.0 Beta 1
----------------------
This release is mostly a cleanup and maintenance release that also
improves a number of minor things and fixes one (non-critical) bug.
Some pending API changes and corrections have been folded into this release
in order to make the upcoming V1.0 API as stable as possible.
This release is also about getting feedback from you in case you don't
approve of any of these changes or would like to get additional
API fixes into V1.0.
The release contains a considerable amount of changes in some of the more
critical parts of the software. It's intended for testing and development
environments and not for production environments. For these, it's best to
wait a few weeks for the proper V1.0 release, to allow some time for any
potential problems to show up (if they exist).
If you encounter any such problems, please post them in the discussion group
or open an issue on GitHub or BitBucket (or send me an email).
There also have been a number of minor API changes.
Please see the README for more information.
New Features
~~~~~~~~~~~~
* official Django 1.3 alpha compatibility
* ``PolymorphicModel.__getattribute__`` hack removed.
This improves performance considerably as python's __getattribute__
generally causes a pretty large processing overhead. It's gone now.
* the ``polymorphic_dumpdata`` management command is not needed anymore
and has been disabled, as the regular Django dumpdata command now automatically
works correctly with polymorphic models (for all supported versions of Django).
* ``.get_real_instances()`` has been elevated to an official part of the API::
real_objects = ModelA.objects.get_real_instances(base_objects_list_or_queryset)
allows you to turn a queryset or list of base objects into a list of the real instances.
This is useful if e.g. you use ``ModelA.base_objects.extra(...)`` and then want to
transform the result to its polymorphic equivalent.
* ``translate_polymorphic_Q_object`` (see DOCS)
* improved testing
* Changelog added: CHANGES.rst/html
Bugfixes
~~~~~~~~
* Removed requirement for primary key to be an IntegerField.
Thanks to Mathieu Steele and Malthe Borch.
API Changes
~~~~~~~~~~~
**polymorphic_dumpdata**
The management command ``polymorphic_dumpdata`` is not needed anymore
and has been disabled, as the regular Django dumpdata command now automatically
works correctly with polymorphic models (for all supported versions of Django).
**Output of Queryset or Object Printing**
In order to improve compatibility with vanilla Django, printing quersets
(__repr__ and __unicode__) does not use django_polymorphic's pretty printing
by default anymore. To get the old behaviour when printing querysets,
you need to replace your model definition:
>>> class Project(PolymorphicModel):
by:
>>> class Project(PolymorphicModel, ShowFieldType):
The mixin classes for pretty output have been renamed:
``ShowFieldTypes, ShowFields, ShowFieldsAndTypes``
are now:
``ShowFieldType, ShowFieldContent and ShowFieldTypeAndContent``
(the old ones still exist for compatibility)
**Running the Test suite with Django 1.3**
Django 1.3 requires ``python manage.py test polymorphic`` instead of
just ``python manage.py test``.
2010-2-22
---------
IMPORTANT: API Changed (import path changed), and Installation Note
The django_polymorphic source code has been restructured
and as a result needs to be installed like a normal Django App
- either via copying the "polymorphic" directory into your
Django project or by running setup.py. Adding 'polymorphic'
to INSTALLED_APPS in settings.py is still optional, however.
The file `polymorphic.py` cannot be used as a standalone
extension module anymore, as is has been split into a number
of smaller files.
Importing works slightly different now: All relevant symbols are
imported directly from 'polymorphic' instead from
'polymorphic.models'::
# new way
from polymorphic import PolymorphicModel, ...
# old way, doesn't work anymore
from polymorphic.models import PolymorphicModel, ...
+ minor API addition: 'from polymorphic import VERSION, get_version'
New Features
~~~~~~~~~~~~
Python 2.4 compatibility, contributed by Charles Leifer. Thanks!
Bugfixes
~~~~~~~~
Fix: The exception "...has no attribute 'sub_and_superclass_dict'"
could be raised. (This occurred if a subclass defined __init__
and accessed class members before calling the superclass __init__).
Thanks to Mattias Brändström.
Fix: There could be name conflicts if
field_name == model_name.lower() or similar.
Now it is possible to give a field the same name as the class
(like with normal Django models).
(Found through the example provided by Mattias Brändström)
2010-2-4
--------
New features (and documentation)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
queryset order_by method added
queryset aggregate() and extra() methods implemented
queryset annotate() method implemented
queryset values(), values_list(), distinct() documented; defer(),
only() allowed (but not yet supported)
setup.py added. Thanks to Andrew Ingram.
More about these additions in the docs:
http://bserve.webhop.org/wiki/django_polymorphic/doc
Bugfixes
~~~~~~~~
* fix remaining potential accessor name clashes (but this only works
with Django 1.2+, for 1.1 no changes). Thanks to Andrew Ingram.
* fix use of 'id' model field, replaced with 'pk'.
* fix select_related bug for objects from derived classes (till now
sel.-r. was just ignored)
"Restrictions & Caveats" updated
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Django 1.1 only - the names of polymorphic models must be unique
in the whole project, even if they are in two different apps.
This results from a restriction in the Django 1.1 "related_name"
option (fixed in Django 1.2).
* Django 1.1 only - when ContentType is used in models, Django's
seralisation or fixtures cannot be used. This issue seems to be
resolved for Django 1.2 (changeset 11863: Fixed #7052, Added
support for natural keys in serialization).
2010-1-30
---------
Fixed ContentType related field accessor clash (an error emitted
by model validation) by adding related_name to the ContentType
ForeignKey. This happened if your polymorphc model used a ContentType
ForeignKey. Thanks to Andrew Ingram.
2010-1-29
---------
Restructured django_polymorphic into a regular Django add-on
application. This is needed for the management commands, and
also seems to be a generally good idea for future enhancements
as well (and it makes sure the tests are always included).
The ``poly`` app - until now being used for test purposes only
- has been renamed to ``polymorphic``. See DOCS.rst
("installation/testing") for more info.
2010-1-28
---------
Added the polymorphic_dumpdata management command (github issue 4),
for creating fixtures, this should be used instead of
the normal Django dumpdata command.
Thanks to Charles Leifer.
Important: Using ContentType together with dumpdata generally
needs Django 1.2 (important as any polymorphic model uses
ContentType).
2010-1-26
---------
IMPORTANT - database schema change (more info in change log).
I hope I got this change in early enough before anyone started
to use polymorphic.py in earnest. Sorry for any inconvenience.
This should be the final DB schema now.
Django's ContentType is now used instead of app-label and model-name
This is a cleaner and more efficient solution
Thanks to Ilya Semenov for the suggestion.
docs/conf.py
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# -*- coding: utf-8 -*-
#
# django-polymorphic documentation build configuration file, created by
# sphinx-quickstart on Sun May 19 12:20:47 2013.
#
# This file is execfile()d with the current directory set to its containing dir.
#
# Note that not all possible configuration values are present in this
# autogenerated file.
#
# All configuration values have a default; values that are commented out
# serve to show the default.
import sys, os
# If extensions (or modules to document with autodoc) are in another directory,
# add these directories to sys.path here. If the directory is relative to the
# documentation root, use os.path.abspath to make it absolute, like shown here.
sys.path.insert(0, os.path.abspath('_ext'))
sys.path.insert(0, os.path.abspath('..'))
os.environ['DJANGO_SETTINGS_MODULE'] = 'djangodummy.settings'
# -- General configuration -----------------------------------------------------
# If your documentation needs a minimal Sphinx version, state it here.
#needs_sphinx = '1.0'
# Add any Sphinx extension module names here, as strings. They can be extensions
# coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
extensions = [
'sphinx.ext.autodoc',
'sphinx.ext.graphviz',
'sphinx.ext.intersphinx'
]
# Add any paths that contain templates here, relative to this directory.
templates_path = ['_templates']
# The suffix of source filenames.
source_suffix = '.rst'
# The encoding of source files.
#source_encoding = 'utf-8-sig'
# The master toctree document.
master_doc = 'index'
# General information about the project.
project = u'django-polymorphic'
copyright = u'2013, Bert Constantin, Chris Glass, Diederik van der Boor'
# The version info for the project you're documenting, acts as replacement for
# |version| and |release|, also used in various other places throughout the
# built documents.
#
# The short X.Y version.
version = '0.4.2.dev0'
# The full version, including alpha/beta/rc tags.
release = '0.4.2'
# The language for content autogenerated by Sphinx. Refer to documentation
# for a list of supported languages.
#language = None
# There are two options for replacing |today|: either, you set today to some
# non-false value, then it is used:
#today = ''
# Else, today_fmt is used as the format for a strftime call.
#today_fmt = '%B %d, %Y'
# List of patterns, relative to source directory, that match files and
# directories to ignore when looking for source files.
exclude_patterns = ['_build']
# The reST default role (used for this markup: `text`) to use for all documents.
#default_role = None
# If true, '()' will be appended to :func: etc. cross-reference text.
#add_function_parentheses = True
# If true, the current module name will be prepended to all description
# unit titles (such as .. function::).
#add_module_names = True
# If true, sectionauthor and moduleauthor directives will be shown in the
# output. They are ignored by default.
#show_authors = False
# The name of the Pygments (syntax highlighting) style to use.
pygments_style = 'sphinx'
# A list of ignored prefixes for module index sorting.
#modindex_common_prefix = []
# -- Options for HTML output ---------------------------------------------------
# The theme to use for HTML and HTML Help pages. See the documentation for
# a list of builtin themes.
html_theme = 'default'
# Theme options are theme-specific and customize the look and feel of a theme
# further. For a list of options available for each theme, see the
# documentation.
#html_theme_options = {}
# Add any paths that contain custom themes here, relative to this directory.
#html_theme_path = []
# The name for this set of Sphinx documents. If None, it defaults to
# "<project> v<release> documentation".
#html_title = None
# A shorter title for the navigation bar. Default is the same as html_title.
#html_short_title = None
# The name of an image file (relative to this directory) to place at the top
# of the sidebar.
#html_logo = None
# The name of an image file (within the static path) to use as favicon of the
# docs. This file should be a Windows icon file (.ico) being 16x16 or 32x32
# pixels large.
#html_favicon = None
# Add any paths that contain custom static files (such as style sheets) here,
# relative to this directory. They are copied after the builtin static files,
# so a file named "default.css" will overwrite the builtin "default.css".
html_static_path = ['_static']
# If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
# using the given strftime format.
#html_last_updated_fmt = '%b %d, %Y'
# If true, SmartyPants will be used to convert quotes and dashes to
# typographically correct entities.
#html_use_smartypants = True
# Custom sidebar templates, maps document names to template names.
#html_sidebars = {}
# Additional templates that should be rendered to pages, maps page names to
# template names.
#html_additional_pages = {}
# If false, no module index is generated.
#html_domain_indices = True
# If false, no index is generated.
#html_use_index = True
# If true, the index is split into individual pages for each letter.
#html_split_index = False
# If true, links to the reST sources are added to the pages.
#html_show_sourcelink = True
# If true, "Created using Sphinx" is shown in the HTML footer. Default is True.
#html_show_sphinx = True
# If true, "(C) Copyright ..." is shown in the HTML footer. Default is True.
#html_show_copyright = True
# If true, an OpenSearch description file will be output, and all pages will
# contain a <link> tag referring to it. The value of this option must be the
# base URL from which the finished HTML is served.
#html_use_opensearch = ''
# This is the file name suffix for HTML files (e.g. ".xhtml").
#html_file_suffix = None
# Output file base name for HTML help builder.
htmlhelp_basename = 'django-polymorphicdoc'
# -- Options for LaTeX output --------------------------------------------------
latex_elements = {
# The paper size ('letterpaper' or 'a4paper').
#'papersize': 'letterpaper',
# The font size ('10pt', '11pt' or '12pt').
#'pointsize': '10pt',
# Additional stuff for the LaTeX preamble.
#'preamble': '',
}
# Grouping the document tree into LaTeX files. List of tuples
# (source start file, target name, title, author, documentclass [howto/manual]).
latex_documents = [
('index', 'django-polymorphic.tex', u'django-polymorphic Documentation',
u'Bert Constantin, Chris Glass, Diederik van der Boor', 'manual'),
]
# The name of an image file (relative to this directory) to place at the top of
# the title page.
#latex_logo = None
# For "manual" documents, if this is true, then toplevel headings are parts,
# not chapters.
#latex_use_parts = False
# If true, show page references after internal links.
#latex_show_pagerefs = False
# If true, show URL addresses after external links.
#latex_show_urls = False
# Documents to append as an appendix to all manuals.
#latex_appendices = []
# If false, no module index is generated.
#latex_domain_indices = True
# -- Options for manual page output --------------------------------------------
# One entry per manual page. List of tuples
# (source start file, name, description, authors, manual section).
man_pages = [
('index', 'django-polymorphic', u'django-polymorphic Documentation',
[u'Bert Constantin, Chris Glass, Diederik van der Boor'], 1)
]
# If true, show URL addresses after external links.
#man_show_urls = False
# -- Options for Texinfo output ------------------------------------------------
# Grouping the document tree into Texinfo files. List of tuples
# (source start file, target name, title, author,
# dir menu entry, description, category)
texinfo_documents = [
('index', 'django-polymorphic', u'django-polymorphic Documentation',
u'Bert Constantin, Chris Glass, Diederik van der Boor', 'django-polymorphic', 'One line description of project.',
'Miscellaneous'),
]
# Documents to append as an appendix to all manuals.
#texinfo_appendices = []
# If false, no module index is generated.
#texinfo_domain_indices = True
# How to display URL addresses: 'footnote', 'no', or 'inline'.
#texinfo_show_urls = 'footnote'
# Example configuration for intersphinx: refer to the Python standard library.
intersphinx_mapping = {
#'http://docs.python.org/': None,
'https://docs.djangoproject.com/en/dev': 'https://docs.djangoproject.com/en/dev/_objects',
}
docs/contributing.rst
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Contributing
============
You can contribute to *django-polymorphic* to forking the code on GitHub:
https://github.com/chrisglass/django_polymorphic
Running tests
-------------
We require features to be backed by a unit test.
This way, we can test *django-polymorphic* against new Django versions.
To run the included test suite, execute::
./runtests.py
To test support for multiple Python and Django versions, run tox from the repository root::
pip install tox
tox
The Python versions need to be installed at your system.
On Linux, download the versions at http://www.python.org/download/releases/.
On MacOS X, use Homebrew_ to install other Python versions.
We currently support Python 2.6 and 2.7.
Python 3.3 support is being worked on.
Example project
----------------
The repository (or tar file) contains a complete Django project
that may be used for tests or experiments, without any installation needed.
The management command ``pcmd.py`` in the app ``pexp`` can be used for quick tests
or experiments - modify this file (pexp/management/commands/pcmd.py) to your liking.
Supported Django versions
-------------------------
The current release should be usable with the supported releases of Django;
the current stable release and the previous release. Supporting older Django
versions is a nice-to-have feature, but not mandatory.
In case you need to use *django-polymorphic* with older Django versions,
consider installing a previous version.
.. _Homebrew: http://mxcl.github.io/homebrew/
docs/index.rst
+71
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Welcome to django-polymorphic's documentation!
==============================================
Django-polymorphic simplifies using inherited models in Django projects.
When a query is made at the base model, the inherited model classes are returned.
When we store models that derive from a ``Project`` model...
>>> 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")
...and want to retrieve all our projects, the subclassed models are returned!
>>> 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"> ]
Using vanilla Django, we get the base class objects, which is rarely what we wanted:
>>> Project.objects.all()
[ <Project: id 1, topic "Department Party">,
<Project: id 2, topic "Painting with Tim">,
<Project: id 3, topic "Swallow Aerodynamics"> ]
Features
--------
* Full admin integation.
* ORM integration:
* support for ForeignKey, ManyToManyField, OneToOneField descriptors.
* support for proxy models
* Filtering/ordering of derived models (``ArtProject___artist``).
* Filtering model types: ``instance_of(...)`` and ``not_instance_of(...)``
* Combining querysets of different models (``qs3 = qs1 | qs2``)
* Support for custom user-defined managers.
* Uses the minumum amount of queries needed to fetch the derived models.
* Disabling polymorphic behavior when needed.
Getting started
---------------
.. toctree::
:maxdepth: 2
quickstart
admin
performance
Advanced topics
---------------
.. toctree::
:maxdepth: 2
advanced
managers
changelog
contributing
Indices and tables
==================
* :ref:`genindex`
* :ref:`modindex`
* :ref:`search`
docs/make.bat
+190
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@ECHO OFF
REM Command file for Sphinx documentation
if "%SPHINXBUILD%" == "" (
set SPHINXBUILD=sphinx-build
)
set BUILDDIR=_build
set ALLSPHINXOPTS=-d %BUILDDIR%/doctrees %SPHINXOPTS% .
set I18NSPHINXOPTS=%SPHINXOPTS% .
if NOT "%PAPER%" == "" (
set ALLSPHINXOPTS=-D latex_paper_size=%PAPER% %ALLSPHINXOPTS%
set I18NSPHINXOPTS=-D latex_paper_size=%PAPER% %I18NSPHINXOPTS%
)
if "%1" == "" goto help
if "%1" == "help" (
:help
echo.Please use `make ^<target^>` where ^<target^> is one of
echo. html to make standalone HTML files
echo. dirhtml to make HTML files named index.html in directories
echo. singlehtml to make a single large HTML file
echo. pickle to make pickle files
echo. json to make JSON files
echo. htmlhelp to make HTML files and a HTML help project
echo. qthelp to make HTML files and a qthelp project
echo. devhelp to make HTML files and a Devhelp project
echo. epub to make an epub
echo. latex to make LaTeX files, you can set PAPER=a4 or PAPER=letter
echo. text to make text files
echo. man to make manual pages
echo. texinfo to make Texinfo files
echo. gettext to make PO message catalogs
echo. changes to make an overview over all changed/added/deprecated items
echo. linkcheck to check all external links for integrity
echo. doctest to run all doctests embedded in the documentation if enabled
goto end
)
if "%1" == "clean" (
for /d %%i in (%BUILDDIR%\*) do rmdir /q /s %%i
del /q /s %BUILDDIR%\*
goto end
)
if "%1" == "html" (
%SPHINXBUILD% -b html %ALLSPHINXOPTS% %BUILDDIR%/html
if errorlevel 1 exit /b 1
echo.
echo.Build finished. The HTML pages are in %BUILDDIR%/html.
goto end
)
if "%1" == "dirhtml" (
%SPHINXBUILD% -b dirhtml %ALLSPHINXOPTS% %BUILDDIR%/dirhtml
if errorlevel 1 exit /b 1
echo.
echo.Build finished. The HTML pages are in %BUILDDIR%/dirhtml.
goto end
)
if "%1" == "singlehtml" (
%SPHINXBUILD% -b singlehtml %ALLSPHINXOPTS% %BUILDDIR%/singlehtml
if errorlevel 1 exit /b 1
echo.
echo.Build finished. The HTML pages are in %BUILDDIR%/singlehtml.
goto end
)
if "%1" == "pickle" (
%SPHINXBUILD% -b pickle %ALLSPHINXOPTS% %BUILDDIR%/pickle
if errorlevel 1 exit /b 1
echo.
echo.Build finished; now you can process the pickle files.
goto end
)
if "%1" == "json" (
%SPHINXBUILD% -b json %ALLSPHINXOPTS% %BUILDDIR%/json
if errorlevel 1 exit /b 1
echo.
echo.Build finished; now you can process the JSON files.
goto end
)
if "%1" == "htmlhelp" (
%SPHINXBUILD% -b htmlhelp %ALLSPHINXOPTS% %BUILDDIR%/htmlhelp
if errorlevel 1 exit /b 1
echo.
echo.Build finished; now you can run HTML Help Workshop with the ^
.hhp project file in %BUILDDIR%/htmlhelp.
goto end
)
if "%1" == "qthelp" (
%SPHINXBUILD% -b qthelp %ALLSPHINXOPTS% %BUILDDIR%/qthelp
if errorlevel 1 exit /b 1
echo.
echo.Build finished; now you can run "qcollectiongenerator" with the ^
.qhcp project file in %BUILDDIR%/qthelp, like this:
echo.^> qcollectiongenerator %BUILDDIR%\qthelp\django-polymorphic.qhcp
echo.To view the help file:
echo.^> assistant -collectionFile %BUILDDIR%\qthelp\django-polymorphic.ghc
goto end
)
if "%1" == "devhelp" (
%SPHINXBUILD% -b devhelp %ALLSPHINXOPTS% %BUILDDIR%/devhelp
if errorlevel 1 exit /b 1
echo.
echo.Build finished.
goto end
)
if "%1" == "epub" (
%SPHINXBUILD% -b epub %ALLSPHINXOPTS% %BUILDDIR%/epub
if errorlevel 1 exit /b 1
echo.
echo.Build finished. The epub file is in %BUILDDIR%/epub.
goto end
)
if "%1" == "latex" (
%SPHINXBUILD% -b latex %ALLSPHINXOPTS% %BUILDDIR%/latex
if errorlevel 1 exit /b 1
echo.
echo.Build finished; the LaTeX files are in %BUILDDIR%/latex.
goto end
)
if "%1" == "text" (
%SPHINXBUILD% -b text %ALLSPHINXOPTS% %BUILDDIR%/text
if errorlevel 1 exit /b 1
echo.
echo.Build finished. The text files are in %BUILDDIR%/text.
goto end
)
if "%1" == "man" (
%SPHINXBUILD% -b man %ALLSPHINXOPTS% %BUILDDIR%/man
if errorlevel 1 exit /b 1
echo.
echo.Build finished. The manual pages are in %BUILDDIR%/man.
goto end
)
if "%1" == "texinfo" (
%SPHINXBUILD% -b texinfo %ALLSPHINXOPTS% %BUILDDIR%/texinfo
if errorlevel 1 exit /b 1
echo.
echo.Build finished. The Texinfo files are in %BUILDDIR%/texinfo.
goto end
)
if "%1" == "gettext" (
%SPHINXBUILD% -b gettext %I18NSPHINXOPTS% %BUILDDIR%/locale
if errorlevel 1 exit /b 1
echo.
echo.Build finished. The message catalogs are in %BUILDDIR%/locale.
goto end
)
if "%1" == "changes" (
%SPHINXBUILD% -b changes %ALLSPHINXOPTS% %BUILDDIR%/changes
if errorlevel 1 exit /b 1
echo.
echo.The overview file is in %BUILDDIR%/changes.
goto end
)
if "%1" == "linkcheck" (
%SPHINXBUILD% -b linkcheck %ALLSPHINXOPTS% %BUILDDIR%/linkcheck
if errorlevel 1 exit /b 1
echo.
echo.Link check complete; look for any errors in the above output ^
or in %BUILDDIR%/linkcheck/output.txt.
goto end
)
if "%1" == "doctest" (
%SPHINXBUILD% -b doctest %ALLSPHINXOPTS% %BUILDDIR%/doctest
if errorlevel 1 exit /b 1
echo.
echo.Testing of doctests in the sources finished, look at the ^
results in %BUILDDIR%/doctest/output.txt.
goto end
)
:end
docs/managers.rst
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Custom Managers, Querysets & Manager Inheritance
================================================
Using a Custom Manager
----------------------
A nice feature of Django is the possibility to define one's own custom object managers.
This is fully supported with django_polymorphic: For creating a custom polymorphic
manager class, just derive your manager from ``PolymorphicManager`` instead of
``models.Manager``. As with vanilla Django, in your model class, you should
explicitly add the default manager first, and then your custom manager::
from polymorphic import PolymorphicModel, PolymorphicManager
class TimeOrderedManager(PolymorphicManager):
def get_query_set(self):
qs = super(TimeOrderedManager,self).get_query_set()
return qs.order_by('-start_date') # order the queryset
def most_recent(self):
qs = self.get_query_set() # get my ordered queryset
return qs[:10] # limit => get ten most recent entries
class Project(PolymorphicModel):
objects = PolymorphicManager() # add the default polymorphic manager first
objects_ordered = TimeOrderedManager() # then add your own manager
start_date = DateTimeField() # project start is this date/time
The first manager defined ('objects' in the example) is used by
Django as automatic manager for several purposes, including accessing
related objects. It must not filter objects and it's safest to use
the plain ``PolymorphicManager`` here.
Manager Inheritance
-------------------
Polymorphic models inherit/propagate all managers from their
base models, as long as these are polymorphic. This means that all
managers defined in polymorphic base models continue to work as
expected in models inheriting from this base model::
from polymorphic import PolymorphicModel, PolymorphicManager
class TimeOrderedManager(PolymorphicManager):
def get_query_set(self):
qs = super(TimeOrderedManager,self).get_query_set()
return qs.order_by('-start_date') # order the queryset
def most_recent(self):
qs = self.get_query_set() # get my ordered queryset
return qs[:10] # limit => get ten most recent entries
class Project(PolymorphicModel):
objects = PolymorphicManager() # add the default polymorphic manager first
objects_ordered = TimeOrderedManager() # then add your own manager
start_date = DateTimeField() # project start is this date/time
class ArtProject(Project): # inherit from Project, inheriting its fields and managers
artist = models.CharField(max_length=30)
ArtProject inherited the managers ``objects`` and ``objects_ordered`` from Project.
``ArtProject.objects_ordered.all()`` will return all art projects ordered
regarding their start time and ``ArtProject.objects_ordered.most_recent()``
will return the ten most recent art projects.
.
Using a Custom Queryset Class
-----------------------------
The ``PolymorphicManager`` class accepts one initialization argument,
which is the queryset class the manager should use. Just as with vanilla Django,
you may define your own custom queryset classes. Just use PolymorphicQuerySet
instead of Django's QuerySet as the base class::
from polymorphic import PolymorphicModel, PolymorphicManager, PolymorphicQuerySet
class MyQuerySet(PolymorphicQuerySet):
def my_queryset_method(...):
...
class MyModel(PolymorphicModel):
my_objects=PolymorphicManager(MyQuerySet)
...
docs/performance.rst
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.. _performance:
Performance Considerations
==========================
Usually, when Django users create their own polymorphic ad-hoc solution
without a tool like *django-polymorphic*, this usually results in a variation of ::
result_objects = [ o.get_real_instance() for o in BaseModel.objects.filter(...) ]
which has very bad performance, as it introduces one additional
SQL query for every object in the result which is not of class ``BaseModel``.
Compared to these solutions, *django-polymorphic* has the advantage
that it only needs 1 SQL query per *object type*, and not *per object*.
The current implementation is does not use any custom SQL or Django DB layer
internals - it is purely based on the standard Django ORM. Specifically, the query::
result_objects = list( ModelA.objects.filter(...) )
performs one SQL query to retrieve ``ModelA`` objects and one additional
query for each unique derived class occurring in result_objects.
The best case for retrieving 100 objects is 1 SQL query if all are
class ``ModelA``. If 50 objects are ``ModelA`` and 50 are ``ModelB``, then
two queries are executed. The pathological worst case is 101 db queries if
result_objects contains 100 different object types (with all of them
subclasses of ``ModelA``).
Database notes
--------------
Current relational DBM systems seem to have general problems with
the SQL queries produced by object relational mappers like the Django
ORM, if these use multi-table inheritance like Django's ORM does.
The "inner joins" in these queries can perform very badly.
This is independent of django_polymorphic and affects all uses of
multi table Model inheritance.
Please also see this `post (and comments) from Jacob Kaplan-Moss
<http://www.jacobian.org/writing/concrete-inheritance/>`_.
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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.
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!