How to create apphooks

How to create apphooks

An apphook allows you to attach a Django application to a page. For example, you might have a news application that you’d like integrated with django CMS. In this case, you can create a normal django CMS page without any content of its own, and attach the news application to the page; the news application’s content will be delivered at the page’s URL.

All URLs in that URL path will be passed to the attached application’s URL configs.

The Tutorials section contains a basic guide to getting started with apphooks. This document assumes more familiarity with the CMS generally.

The basics of apphook creation

To create an apphook, create a cms_apps.py file in your application.

The file needs to contain a CMSApp sub-class. For example:

from cms.app_base import CMSApp
from cms.apphook_pool import apphook_pool
@apphook_pool.register
class MyApphook(CMSApp):
    app_name = "myapp"  # must match the application namespace
    name = "My Apphook"
    def get_urls(self, page=None, language=None, **kwargs):
        return ["myapp.urls"] # replace this with the path to your application's URLs module

Changed in version 3.3: CMSApp.get_urls() replaces CMSApp.urls. urls was removed in version 3.5.

Apphooks for namespaced applications

Your application should use namespaced URLs.

In the example above, the application uses the myapp namespace. Your CMSApp sub-class must reflect the application’s namespace in the app_name attribute.

The application may specify a namespace by supplying an app_name in its urls.py, or its documentation might advise that you when include its URLs, you do it thus:

url(r'^myapp/', include('myapp.urls', app_name='myapp'))

If you fail to do this, then any templates in the application that invoke URLs using the form {% url 'myapp:index' %} or views that call (for example) reverse('myapp:index') will throw a NoReverseMatch error.

Apphooks for non-namespaced applications

If you are writing apphooks for third-party applications, you may find one that in fact does not have an application namespace for its URLs. Such an application is liable to tun into namespace conflicts, and doesn’t represent good practice.

However if you do encounter such an application, your own apphook for it will need in turn to forgo the app_name attribute.

Note that unlike apphooks without app_name attributes can be attached only to one page at a time; attempting to apply them a second time will cause an error. Only one instance of these apphooks can exist.

See Attaching an application multiple times for more on having multiple apphook instances.

Returning apphook URLs manually

Instead of defining the URL patterns in another file myapp/urls.py, it also is possible to return them manually, for example if you need to override the set provided. An example:

from django.conf.urls import url
from myapp.views import SomeListView, SomeDetailView
class MyApphook(CMSApp):
    # ...
    def get_urls(self, page=None, language=None, **kwargs):
        return [
            url(r'^$', SomeListView.as_view()),
            url(r'^(?P<slug>[\w-]+)/?$', SomeDetailView.as_view()),
            ]

However, it’s much neater to keep them in the application’s urls.py, where they can easily be reused.

Loading new and re-configured apphooks

Certain apphook-related changes require server restarts in order to be loaded.

Whenever you:

add or remove an apphook
change the slug of a page containing an apphook or the slug of a page which has a descendant with an apphook

the URL caches must be reloaded.

If you have the cms.middleware.utils.ApphookReloadMiddleware installed, which is recommended, the server will do it for you by re-initialising the URL patterns automatically.

Otherwise, you will need to restart the server manually.

Using an apphook

Once your apphook has been set up and loaded, you’ll now be able to select the Application that’s hooked into that page from its Advanced settings.

Note

An apphook won’t actually do anything until the page it belongs to is published. Take note that this also means all parent pages must also be published.

The apphook attaches all of the apphooked application’s URLs to the page; its root URL will be the page’s own URL, and any lower-level URLs will be on the same URL path.

So, given an application with the urls.py for the views index_view and archive_view:

urlpatterns = [
    url(r'^$', index_view),
    url(r'^archive/$', archive_view),
]

attached to a page whose URL path is /hello/world/, the views will be exposed as follows:

index_view at /hello/world/
archive_view at /hello/world/archive/

Sub-pages of an apphooked page

Important

Don’t add child pages to a page with an apphook.

The apphook “swallows” all URLs below that of the page, handing them over to the attached application. If you have any child pages of the apphooked page, django CMS will not be able to serve them reliably.

Managing apphooks

Uninstalling an apphook with applied instances

If you remove an apphook class from your system (in effect uninstalling it) that still has instances applied to pages, django CMS tries to handle this as gracefully as possible:

Affected pages still maintain a record of the applied apphook; if the apphook class is subsequently reinstated, it will work as before.
The page list will show apphook indicators where appropriate.
The page will otherwise behave like a normal django CMS page, and display its placeholders in the usual way.
If you save the page’s Advanced settings, the apphook will be removed.

Management commands

You can clear uninstalled apphook instances using the CMS management command uninstall apphooks. For example:

manage.py cms uninstall apphooks MyApphook MyOtherApphook

You can get a list of installed apphooks using the cms list; in this case:

manage.py cms list apphooks

See the Management commands reference for more information.

Adding menus to apphooks

Generally, it is recommended to allow the user to control whether a menu is attached to a page (See Attach Menus for more on these menus). However, an apphook can be made to do this automatically if required. It will behave just as if the menu had been attached to the page using its Advanced settings).

Menus can be added to an apphook using the get_menus() method. On the basis of the example above:

# [...]
from myapp.cms_menus import MyAppMenu
class MyApphook(CMSApp):
    # [...]
    def get_menus(self, page=None, language=None, **kwargs):
        return [MyAppMenu]

Changed in version 3.3: CMSApp.get_menus() replaces CMSApp.menus. The menus attribute is now deprecated and has been removed in version 3.5.

The menus returned in the get_menus() method need to return a list of nodes, in their get_nodes() methods. Attach Menus has more information on creating menu classes that generate nodes.

You can return multiple menu classes; all will be attached to the same page:

def get_menus(self, page=None, language=None, **kwargs):
    return [MyAppMenu, CategoryMenu]

Managing permissions on apphooks

By default the content represented by an apphook has the same permissions set as the page it is assigned to. So if for example a page requires the user to be logged in, then the attached apphook and all its URLs will have the same requirements.

To disable this behaviour set permissions = False on your apphook:

class MyApphook(CMSApp):
    [...]
    permissions = False

If you still want some of your views to use the CMS’s permission checks you can enable them via a decorator, cms.utils.decorators.cms_perms

Here is a simple example:

from cms.utils.decorators import cms_perms
@cms_perms
def my_view(request, **kw):
    ...

If you make your own permission checks in your application, then use the exclude_permissions property of the apphook:

class MyApphook(CMSApp):
    [...]
    permissions = True
    exclude_permissions = ["some_nested_app"]

where you provide the name of the application in question

Automatically restart server on apphook changes

As mentioned above, whenever you:

add or remove an apphook
change the slug of a page containing an apphook
change the slug of a page with a descendant with an apphook

The CMS the server will reload its URL caches. It does this by listening for the signal cms.signals.urls_need_reloading.

Warning

This signal does not actually do anything itself. For automated server restarting you need to implement logic in your project that gets executed whenever this signal is fired. Because there are many ways of deploying Django applications, there is no way we can provide a generic solution for this problem that will always work.

The signal is fired after a request - for example, upon saving a page’s settings. If you change and apphook’s setting via an API the signal won’t fire until a subsequent request.

Apphooks and placeholder template tags

It’s important to understand that while an apphooked application takes over the CMS page at that location completely, depending on how the application’s templates extend other templates, a django CMS {% placeholder %} template tag may be invoked - but will not work.

{% static_placeholder %} tags on the other hand are not page-specific and will function normally.

Create apphooks