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- <div class="document">
- <div class="section" id="polymorphic-models-for-django">
- <h1>Polymorphic Models for Django</h1>
- <div class="section" id="quick-start-docs-contributing">
- <h2>Quick Start, Docs, Contributing</h2>
- <ul class="simple">
- <li><a class="reference external" href="#good-for">What is django_polymorphic good for?</a></li>
- <li><a class="reference external" href="http://bserve.webhop.org/django_polymorphic/DOCS.html#quickstart">Quickstart</a>, or the complete <a class="reference external" href="http://bserve.webhop.org/django_polymorphic/DOCS.html">Installation and Usage Docs</a></li>
- <li><a class="reference external" href="http://groups.google.de/group/django-polymorphic/topics">Release Notes, News and Discussion</a> (Google Group) or <a class="reference external" href="http://bserve.webhop.org/django_polymorphic/CHANGES.html">Changelog</a></li>
- <li>Download from <a class="reference external" href="http://github.com/bconstantin/django_polymorphic">GitHub</a> or <a class="reference external" href="http://bitbucket.org/bconstantin/django_polymorphic">Bitbucket</a>, or as <a class="reference external" href="http://github.com/bconstantin/django_polymorphic/tarball/master">TGZ</a> or <a class="reference external" href="http://github.com/bconstantin/django_polymorphic/zipball/master">ZIP</a></li>
- <li>Improve django_polymorphic, report issues, discuss, patch or fork (<a class="reference external" href="http://github.com/bconstantin/django_polymorphic">GitHub</a>, <a class="reference external" href="http://bitbucket.org/bconstantin/django_polymorphic">Bitbucket</a>, <a class="reference external" href="http://groups.google.de/group/django-polymorphic/topics">Group</a>, <a class="reference external" href="http://github.com/bconstantin/django_polymorphic/tree/master/setup.py">Mail</a>)</li>
- </ul>
- </div>
- <div class="section" id="id1">
- <span id="good-for"></span><h2>What is django_polymorphic good for?</h2>
- <p>Let's assume the models <tt class="docutils literal">ArtProject</tt> and <tt class="docutils literal">ResearchProject</tt> are derived
- from the model <tt class="docutils literal">Project</tt>, and let's store one of each into the database:</p>
- <pre class="doctest-block">
- >>> 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")
- </pre>
- <p>If we want to retrieve all our projects, we do:</p>
- <pre class="doctest-block">
- >>> Project.objects.all()
- </pre>
- <p>Using django_polymorphic, we simply get what we stored:</p>
- <pre class="literal-block">
- [ <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"> ]
- </pre>
- <p>Using vanilla Django, we get incomplete objects, which is probably not what we wanted:</p>
- <pre class="literal-block">
- [ <Project: id 1, topic "Department Party">,
- <Project: id 2, topic "Painting with Tim">,
- <Project: id 3, topic "Swallow Aerodynamics"> ]
- </pre>
- <p>It's very similar for ForeignKeys, ManyToManyFields or OneToOneFields.</p>
- <p>In general, the effect of django_polymorphic is twofold:</p>
- <p>On one hand it makes sure that model inheritance just works as you
- expect, by simply ensuring that you always get back exactly the same
- objects from the database you stored there - regardless how you access
- them, making model inheritance much more "pythonic".
- This can save you a lot of unpleasant workarounds that tend to
- make your code messy, error-prone, and slow.</p>
- <p>On the other hand, together with some small API additions to the Django
- ORM, django_polymorphic enables a much more expressive and intuitive
- programming style and also very advanced object oriented designs
- that are not possible with vanilla Django.</p>
- <p>Fortunately, most of the heavy duty machinery that is needed for this
- functionality is already present in the original Django database layer.
- Django_polymorphic adds a rather thin layer above that in order
- to make real OO fully automatic and very easy to use.</p>
- <p>There is a catch however, which applies to concrete model inheritance
- in general: Current DBM systems like PostgreSQL or MySQL are not very
- good at processing the required sql queries and can be rather slow in
- many cases. Concrete benchmarks are forthcoming (please see
- discussion forum).</p>
- <p>For more information, please look at <a class="reference external" href="http://bserve.webhop.org/django_polymorphic/DOCS.html#quickstart">Quickstart</a> or at the complete
- <a class="reference external" href="http://bserve.webhop.org/django_polymorphic/DOCS.html">Installation and Usage Docs</a> and also see the <a class="reference external" href="http://bserve.webhop.org/django_polymorphic/DOCS.html#restrictions">restrictions and caveats</a>.</p>
- </div>
- <div class="section" id="this-is-a-v1-0-beta-testing-release">
- <h2>This is a V1.0 Beta/Testing Release</h2>
- <p>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 turn up (if they exist).</p>
- <p>If you encounter any problems or have suggestions regarding the API or the
- changes in this beta, please post them in the <a class="reference external" href="http://groups.google.de/group/django-polymorphic/topics">discussion group</a>
- or open an issue on <a class="reference external" href="http://github.com/bconstantin/django_polymorphic">GitHub</a> or <a class="reference external" href="http://bitbucket.org/bconstantin/django_polymorphic">BitBucket</a> (or send me an email).</p>
- </div>
- </div>
- <div class="section" id="license">
- <h1>License</h1>
- <p>Django_polymorphic uses the same license as Django (BSD-like).</p>
- </div>
- <div class="section" id="api-changes-additions">
- <h1>API Changes & Additions</h1>
- <div class="section" id="november-11-2010-v1-0-api-changes">
- <h2>November 11 2010, V1.0 API Changes</h2>
- <div class="section" id="extra-queryset-method">
- <h3>extra() queryset method</h3>
- <p><tt class="docutils literal">.extra()</tt> 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 <tt class="docutils literal">polymorphic</tt> keyword parameter has been removed.
- You can get back the non-polymorphic behaviour by using
- <tt class="docutils literal"><span class="pre">ModelA.objects.non_polymorphic().extra()</span></tt>.</p>
- </div>
- <div class="section" id="no-pretty-printing-of-querysets-by-default">
- <h3>No Pretty-Printing of Querysets by default</h3>
- <p>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:</p>
- <pre class="doctest-block">
- >>> class Project(PolymorphicModel):
- </pre>
- <p>by:</p>
- <pre class="doctest-block">
- >>> class Project(PolymorphicModel, ShowFieldType):
- </pre>
- <p>The mixin classes for pretty output have been renamed:</p>
- <blockquote>
- <tt class="docutils literal">ShowFieldTypes, ShowFields, ShowFieldsAndTypes</tt></blockquote>
- <p>are now:</p>
- <blockquote>
- <tt class="docutils literal">ShowFieldType, ShowFieldContent and ShowFieldTypeAndContent</tt></blockquote>
- <p>(the old ones still exist for compatibility)</p>
- </div>
- <div class="section" id="pretty-printing-output-format-changed">
- <h3>Pretty-Printing Output Format Changed</h3>
- <p><tt class="docutils literal">ShowFieldContent</tt> and <tt class="docutils literal">ShowFieldTypeAndContent</tt> 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
- <tt class="docutils literal">polymorphic_showfield_old_format = True</tt> to your model definitions.
- <tt class="docutils literal"><span class="pre">ShowField...</span></tt> now also produces more informative output for custom
- primary keys.</p>
- </div>
- <div class="section" id="polymorphic-dumpdata">
- <h3>polymorphic_dumpdata</h3>
- <p>The <tt class="docutils literal">polymorphic_dumpdata</tt> 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).</p>
- </div>
- <div class="section" id="running-the-test-suite-with-django-1-3">
- <h3>Running the Test suite with Django 1.3</h3>
- <p>Django 1.3 requires <tt class="docutils literal">python manage.py test polymorphic</tt> instead of
- just <tt class="docutils literal">python manage.py test</tt>.</p>
- </div>
- </div>
- <div class="section" id="november-01-2010-v1-0-api-additions">
- <h2>November 01 2010, V1.0 API Additions</h2>
- <ul>
- <li><p class="first"><tt class="docutils literal">.non_polymorphic()</tt> queryset member function added. This is preferable to
- using <tt class="docutils literal"><span class="pre">.base_objects...</span></tt>, as it just makes the resulting queryset non-polymorphic
- and does not change anything else in the behaviour of the manager used (while
- <tt class="docutils literal">.base_objects</tt> is just a different manager).</p>
- </li>
- <li><p class="first"><tt class="docutils literal">.get_real_instances()</tt> has been elevated to an official part of the API.
- It 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 <tt class="docutils literal"><span class="pre">ModelA.objects.non_polymorphic().extra(...)</span></tt> and then want to
- transform the result to its polymorphic equivalent:</p>
- <pre class="doctest-block">
- >>> qs = ModelA.objects.all().non_polymorphic()
- >>> real_objects = qs.get_real_instances()
- </pre>
- <p>is equivalent to:</p>
- <pre class="doctest-block">
- >>> real_objects = ModelA.objects.all()
- </pre>
- <p>Instead of <tt class="docutils literal">qs.get_real_instances()</tt>, <tt class="docutils literal">ModelA.objects.get_real_instances(qs)</tt> may be used
- as well. In the latter case, <tt class="docutils literal">qs</tt> may be any list of objects of type ModelA.</p>
- </li>
- <li><p class="first"><tt class="docutils literal">translate_polymorphic_Q_object</tt> (see DOCS)</p>
- </li>
- </ul>
- </div>
- <div class="section" id="february-22-2010-installation-note">
- <h2>February 22 2010, Installation Note</h2>
- <p>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.</p>
- <p>The file <cite>polymorphic.py</cite> cannot be used as a standalone
- extension module anymore (as is has been split into a number
- of smaller files).</p>
- <p>Importing works slightly different now: All relevant symbols are
- imported directly from 'polymorphic' instead from
- 'polymorphic.models':</p>
- <pre class="literal-block">
- # new way
- from polymorphic import PolymorphicModel, ...
- # old way, doesn't work anymore
- from polymorphic.models import PolymorphicModel, ...
- </pre>
- </div>
- <div class="section" id="january-26-2010-database-schema-change">
- <h2>January 26 2010: Database Schema Change</h2>
- <p>The update from January 26 changed the database schema (more info in the <a class="reference external" href="http://github.com/bconstantin/django_polymorphic/commit/c2b420aea06637966a208329ef7ec853889fa4c7">commit-log</a>).
- Sorry for any inconvenience. But this should be the final DB schema now.</p>
- </div>
- </div>
- </div>
- </body>
- </html>