.. _create-basic-permission:

.. index::
    single: autodiscover
    single: permissions.py
    single: BasePermission

=========================
Create a basic permission
=========================

Where to store permissions?
===========================

First of all: All following permission classes should be placed in a file
called ``permissions.py`` in your application or project-directory. For the 
*why* please have a look on `How permissions are discovered`_.

A basic permission
==================

Let's start with a example::

    import authority
    from authority import permissions
    from django.contrib.flatpages.models import Flatpage

    class FlatpagePermission(permissions.BasePermission):
        label = 'flatpage_permission'

    authority.register(Flatpage, FlatpagePermission)

Let's make the code clear. First of, if you want to create a new permission
you have to subclass it from the BasePermission class::

    from authority import permissions
    class FlatpagePermission(permissions.BasePermission):
        # ...

Next you need to name this permission using the ``label`` attribute::

    class FlatpagePermission(permissions.BasePermission):
        label = 'flatpage_permission'

And finally you need to register the permission to the pool of all other
permissions::

    authority.register(Flatpage, FlatpagePermission)

The syntax of this is simple::

    authority.register(<model>, <permissionclass>)

While this is not much code, you already wrapped Django's basic permissions
(add_flatpage, change_flatpage, delete_flatpage) for the model ``Flatpage``
and you are ready to use it within your templates or code:

.. note:: See `Django's basic permissions`_ how Django creates this permissions for you.

.. _Django's basic permissions: http://docs.djangoproject.com/en/dev/topics/auth/#permissions


Example permission checks
=========================

This section shows you how to check for Django's basic permissions with
django-authorit

In your python code
-------------------
::

    def my_view(request):    
        check = FlatPagePermission(request.user)
        if check.change_flatpage():
            print "Yay, you can change a flatpage!"

Using the view decorator
------------------------
::

    from authority.decorators import permission_required_or_403

    @permission_required_or_403('flatpage_permission.change_flatpage')
    def my_view(request):
        # ...
        
See :ref:`check-decorator` how the decorator works in detail.
        
In your templates
-----------------
::

    {% ifhasperm "flatpage_permission.change_flatpage" request.user %}
        Yay, you can change a flatpage!
    {% else %}
        Nope, sorry. You aren't allowed to change a flatpage.
    {% endifhasperm %}

See :ref:`check-templates` how the templatetag works in detail.

How permissions are discovered
==============================

On first runtime of your project ``authority.autodiscover()`` will load all
``permission.py`` files that are in your ``settings.INSTALLED_APPS``
applications. See :ref:`configuration` how to set up ``autodiscover``.

.. image:: .static/authority-permission-py.png
   :align: left
   
We encourage you to place your permission-classes in a file called
``permission.py`` inside your project or application directory. Not only that
this behaviour will keep your application structure clean, if you use
``authority.autodiscover()`` it's guaranteed that every permission-class is
loaded at runtime.

If you really want, you can place these permission-classes in other files
that are loaded at runtime. ``__init__.py`` or ``models.py`` are such files.