367 lines
13 KiB
HTML
367 lines
13 KiB
HTML
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</head>
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<body>
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<div class="document">
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<div class="section" id="polymorphic-models-for-django">
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<h1>Polymorphic Models for Django</h1>
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<p>.</p>
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<div class="section" id="quick-start-docs-contributing">
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<h2>Quick Start, Docs, Contributing</h2>
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<ul class="simple">
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<li><a class="reference external" href="#good-for">What is django_polymorphic good for?</a></li>
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<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>
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<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>
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<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>
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<li>Improve django_polymorphic, report issues, participate, 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>
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</ul>
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</div>
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<div class="section" id="id1">
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<span id="good-for"></span><h2>What is django_polymorphic good for?</h2>
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<p>If you work with Django's model inheritance, django_polymorphic might
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save you from implementing unpleasant workarounds that make your code
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messy, error-prone, and slow. Model inheritance becomes much more "pythonic"
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and now just works as you as a Python programmer expect.</p>
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</div>
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<div class="section" id="it-s-best-to-look-at-an-example">
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<h2>It's best to Look at an Example</h2>
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<p>Let's assume the models <tt class="docutils literal">ArtProject</tt> and <tt class="docutils literal">ResearchProject</tt> are derived
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from the model <tt class="docutils literal">Project</tt>, and let's store one of each into the database:</p>
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<pre class="doctest-block">
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>>> Project.objects.create(topic="John's Gathering")
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>>> ArtProject.objects.create(topic="Sculpting with Tim", artist="T. Turner")
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>>> ResearchProject.objects.create(topic="Swallow Aerodynamics", supervisor="Dr. Winter")
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</pre>
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<p>If we want to retrieve all our projects, we do:</p>
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<pre class="doctest-block">
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>>> Project.objects.all()
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</pre>
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<p>Using django_polymorphic, we simply get what we stored:</p>
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<pre class="literal-block">
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[ <Project: id 1, topic: "John's Gathering">,
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<ArtProject: id 2, topic: "Sculpting with Tim", artist: "T. Turner">,
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<ResearchProject: id 3, topic: "Swallow Aerodynamics", supervisor: "Dr. Winter"> ]
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</pre>
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<p>Using vanilla Django, we get incomplete objects, which is probably not what we wanted:</p>
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<pre class="literal-block">
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[ <Project: id 1, topic: "John's Gathering">,
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<Project: id 2, topic: "Sculpting with Tim">,
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<Project: id 3, topic: "Swallow Aerodynamics"> ]
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</pre>
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<p>It's very similar for ForeignKeys, ManyToManyFields or OneToOneFields.</p>
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<p>In general, the effect of django_polymorphic is twofold:</p>
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<p>On one hand it makes sure that model inheritance just works
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as you expect, by simply ensuring that you always get back exactly the same
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objects from the database you stored there - regardless how you access them.
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This can save you a lot of unpleasant workarounds.</p>
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<p>On the other hand, together with only few small API additions to the Django ORM,
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django_polymorphic enables a much more expressive and intuitive
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programming style and also very advanced object oriented
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designs that are not possible with vanilla Django.</p>
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<p>Fortunately, most of the heavy duty machinery that is needed for this
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functionality is already present in the original Django database layer.
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Django_polymorphic merely adds a rather thin layer above that, which is
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all that is required to make real OO fully automatic and very easy to use,
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with only minimal additions to Django's API.</p>
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<p>For more information, please look at <a class="reference external" href="http://bserve.webhop.org/django_polymorphic/DOCS.html#quickstart">Quickstart</a> or the complete
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<a class="reference external" href="http://bserve.webhop.org/django_polymorphic/DOCS.html">Installation and Usage Docs</a>. Please also see the <a class="reference external" href="http://bserve.webhop.org/django_polymorphic/DOCS.html#restrictions">restrictions and caveats</a>.</p>
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</div>
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<div class="section" id="this-is-a-v1-0-beta-testing-release">
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<h2>This is a V1.0 Beta/Testing Release</h2>
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<p>This release is mostly a cleanup and maintenance release that also
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improves a number of minor things and fixes one (non-critical) bug.</p>
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<p>Some pending API changes and corrections have been folded into this release
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in order to make the upcoming V1.0 API as stable as possible.</p>
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<p>This release is also about getting feedback from you in case you don't
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approve of any of these changes or would like to get additional
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API fixes into V1.0.</p>
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<p>The release contains a considerable amount of changes in some of the more
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critical parts of the software. It's intended for testing and development
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environments and not for production environments. For these, it's best to
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wait a few weeks for the proper V1.0 release, to allow some time for any
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potential problems to turn up (if they exist).</p>
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<p>If you encounter any problems please post them in the <a class="reference external" href="http://groups.google.de/group/django-polymorphic/topics">discussion group</a>
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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>
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</div>
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</div>
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<div class="section" id="license">
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<h1>License</h1>
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<p>Django_polymorphic uses the same license as Django (BSD-like).</p>
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</div>
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<div class="section" id="api-changes">
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<h1>API Changes</h1>
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<div class="section" id="october-18-2010">
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<h2>October 18 2010</h2>
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<div class="section" id="polymorphic-dumpdata">
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<h3>polymorphic_dumpdata</h3>
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<p>The polymorphic_dumpdata management command is not needed anymore
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and has been removed, as the regular Django dumpdata command now automatically
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works correctly with polymorphic models (for all supported versions of Django).</p>
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</div>
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<div class="section" id="output-of-queryset-or-object-printing">
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<h3>Output of Queryset or Object Printing</h3>
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<p>In order to improve compatibility with vanilla Django, printing quersets does not use
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django_polymorphic's pretty printing by default anymore.
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To get the old behaviour when printing querysets, you need to replace your model definition:</p>
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<pre class="doctest-block">
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>>> class Project(PolymorphicModel):
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</pre>
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<p>by:</p>
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<pre class="doctest-block">
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>>> class Project(PolymorphicModel, ShowFieldType):
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</pre>
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<p>The mixin classes for pretty output have been renamed:</p>
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<blockquote>
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<tt class="docutils literal">ShowFieldTypes, ShowFields, ShowFieldsAndTypes</tt></blockquote>
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<p>are now:</p>
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<blockquote>
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<tt class="docutils literal">ShowFieldType, ShowFieldContent and ShowFieldTypeAndContent</tt></blockquote>
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<p>(the old ones still exist for compatibility)</p>
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</div>
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<div class="section" id="running-the-test-suite-with-django-1-3">
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<h3>Running the Test suite with Django 1.3</h3>
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<p>Django 1.3 requires <tt class="docutils literal">python manage.py test polymorphic</tt> instead of
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just <tt class="docutils literal">python manage.py test</tt>.</p>
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</div>
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</div>
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<div class="section" id="february-22-2010-installation-note">
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<h2>February 22 2010, Installation Note</h2>
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<p>The django_polymorphic source code has been restructured
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and as a result needs to be installed like a normal Django App
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- either via copying the "polymorphic" directory into your
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Django project or by running setup.py. Adding 'polymorphic'
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to INSTALLED_APPS in settings.py is still optional, however.</p>
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<p>The file <cite>polymorphic.py</cite> cannot be used as a standalone
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extension module anymore (as is has been split into a number
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of smaller files).</p>
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<p>Importing works slightly different now: All relevant symbols are
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imported directly from 'polymorphic' instead from
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'polymorphic.models':</p>
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<pre class="literal-block">
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# new way
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from polymorphic import PolymorphicModel, ...
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# old way, doesn't work anymore
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from polymorphic.models import PolymorphicModel, ...
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</pre>
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</div>
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<div class="section" id="january-26-2010-database-schema-change">
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<h2>January 26 2010: Database Schema Change</h2>
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<div class="line-block">
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<div class="line">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>).</div>
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<div class="line">Sorry for any inconvenience. But this should be the final DB schema now.</div>
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</div>
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</div>
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</div>
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</div>
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</body>
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