Hi all,
URL namespaces have a few quirks that make them a bit difficult to use and
understand. I hope to create a patch that clears up these issues.
First up: the distinction between an application namespace and an instance
namespace. The docs say on the application namespace:
This describes the name of the application that is being deployed. Every
> instance of a single application will have the same application namespace.
And on the instance namespace:
This identifies a specific instance of an application. Instance namespaces
> should be unique across your entire project. However, an instance namespace
> can be the same as the application namespace. This is used to specify a
> default instance of an application.
The current implementation requires that both are specified in the same
place: either in the included url configuration by returning a 3-tuple, or
in the including url configuration through the arguments to include(). The
first case generally does not allow multiple deployments of the same app,
unless the included url configuration contains specific logic to return
different instance namespaces. The second case does not in any way enforce
that multiple deployments in fact have the same application namespace.
I'd like to get the semantics and the implementation in line, and provide
one obvious way to specify namespaces. Including a set of url patterns
under a namespace involves two parts: the including urlconf that calls
include(), and the included urlconf that is imported by include(). The
first is a specific deployment of the imported urlconf; the second is a
single app.
The obvious way as I see it would be to specify the application namespace
in the app, and specify the instance namespace as a parameter to include().
This enforces the single application namespace for a single set of
patterns, and allows any end-user to specify the instance namespace on a
per-instance basis. To take the admin as an example:
admin.site.urls would return a 2-tuple: (patterns, 'admin'), where 'admin'
is the application namespace. (An alternative to a 2-tuple could be an
object with urlpatterns and app_name attributes.)
To include the admin instance, use include(admin.site.urls,
namespace='admin'). This is the instance namespace. If left out, it could
default to be the same as the app name.
After a deprecation period, it would be an error to specify an instance
namespace if there is no application namespace. This is to ensure that the
app can always reverse its own urls using <app_name>:<view_name> if it
specifies an application namespace, and using <view_name> if it doesn't.
(Setting and app_name would technically still be possible by passing a
hardcoded (patterns, app_name) tuple, just not as an advertised feature.)
The second point is about nested namespace handling and current_app.
At the moment, current_app is looking for an exact namespace match. Unlike
the namespaced view path, it is not split into namespace parts using
current_app.split(':'). Take the following (fictional) urlpatterns:
blog_patterns = [
url(r'^comments-one/', include('comments.urls', 'comments-one',
'comments')),
url(r'^comments-two/', include('comments.urls', 'comments-two',
'comments')),
]
urlpatterns = [
url(r'^blog-one/', include(blog_patterns, 'blog-one', 'blog')),
url(r'^blog-two/', include(blog_patterns, 'blog-two', 'blog')),
]
Because of how current_app is handled, it is now impossible to reverse
patterns in 'blog-one:comments-one:' using current_app. To select
'blog-one', the current app needs to be the string 'blog-one', but to
select 'comments-one', it needs to be 'comments-one'. The only solution is
to hardcode at least one of the instance namespaces in the namespaced view
path. This also means that setting request.current_app to
request.resolver_match.namespace, as recommended in the docs, does not work
if you have nested namespaces.
The ResolverMatch object also has some inconsistent behaviour for app_name.
resolver_match.namespace is the full namespace path, i.e.
'blog-one:comments-one' (with resolver_match.namespaces a list of
individual namespaces, i.e. ['blog-one', 'comments-one']), but
resolver_match.app_name is the outer-most app_name, in this case
'blog-one', with no trace whatsoever of the full app_name path.
To illustrate how I would see it end up eventually (after the deprecation
cycle), I've created a branch at
https://github.com/knbk/django/tree/namespaces. I feel these changes are
fairly straightforward, but any comments are appreciated.
Marten
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