Django appregister

Django appregister is a building blocks app to implement a class registry system for your django app. It uses a similar approach to the Django admin, allowing you to register classes and supports an autodiscover feature.

A register based system provides a good base for making an app plugable and extendable by third parties as they can register their own subclasses and your code is able to use them.

Installation

Use pip:

pip install django-appregister

Quick Example Usage

First, you should create your base class that all registered classes will be a subclass of. Often this is a base Model class in your models.py but it can be any python class anywhere in your project.

>>> class AppPlugin(object):
...     pass

You then need to declare your register. It only had one required property; base. The base can either be a class object, or a dotted string to the class, such as "myapp.AppPlugin".

The other most common property is the discovermodule property. This provides a way to automatically discover subclasses within a project. You can choose any name here that would make a valid Python package name and then appregister will look through the INSTALLED_APPS in your Django settings and find registered items. For example, if you use the discovermodule value plugins and have the app myblog in your installed apps, then app register will look in myblog.plugins for registered classes.

>>> from appregister import SortedRegistry

>>> class MyRegistry(SortedRegistry):
...     base = AppPlugin
...     discovermodule = 'plugins'

After that, you can go ahead and create an instance of the registry - creating it at the module level makes it easy to re-use across the project (but you can have as many instances as you need). It’s good practice to create your registry in its own module, such as myapp/register.py.

>>> plugins = MyRegistry()

Now that we have the registry, if you want to use the autodiscover feature you will need to add the following line in your base urls.py. Exactly like you do for the Django admin. Import the registry instance from where you stored it and then call autodiscover.

>>> plugins.autodiscover()

Now that you have the registry, you can start to add subclasses to it. This can be done by using the class decorator on your register.

>>> @plugins.register
... class MyPlugin(AppPlugin):
...     pass

Note

If you are using version 2.5 or below of Python you can’t use the class based decorator, you will need to call it manually. The above example would then become;

>>> class MySecondPlugin(AppPlugin):
...     pass
>>> plugins.register(MySecondPlugin)
<class 'MySecondPlugin'>

Registering an invalid object will raise an InvalidOperation exception

>>> # Note that this class does not inherit from the base we specified.
>>> class MyNonSubclass(object):
...     pass

>>> plugins.register(MyNonSubclass)
Traceback (most recent call last):
    ...
InvalidOperation: Object 'MyNonSubclass' is not a subclass of 'AppPlugin'

Finally, now you can get all your objects back - this includes those registered by a third party.

>>> len(plugins)
2

>>> for plugin in plugins:
...     print plugin
<class 'MyPlugin'>
<class 'MySecondPlugin'>

Note

The order of registration is not stored. Since we can’t tell what order they would be registered, if you want a sorted set you will need to sort them after they have all been registered.

>>> plugins.clear()
>>> len(plugins)
0

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