Recommended middleware syntax fails for some testing cases (when not using Client)

[Theodore Diamantidis]

It is common for developers to prefer RequestFactory over Client in unit testing, or any similar module that mocks requests without processing the URLs or applying the enabled middleware. So, when a unit test needs to test a view while using a middleware, the easiest way to do so is:

from django.test import RequestFactory

from .views import MyView
from .middleware import MyMiddleware

request = RequestFactory().get('/')
view = MyMiddleware(MyView)
response = view(request)

Also, it may be needed to test views that accept arguments (e.g. captured URL parameters), which would probably look like this:

request = RequestFactory().get('/articles/4/')
response = MyView(request, pk=4)

The problem arises when we both use test views that accept parameters and a custom middleware. The current documentation offers examples for writing such a middleware:

def MyMiddleware(get_response):
    # One-time configuration and initialization.

    def middleware(request):
        # Code to be executed for each request before
        # the view (and later middleware) are called.

        response = get_response(request)

        # Code to be executed for each request/response after
        # the view is called.

        return response

    return middleware

Given the above tests, one would expect this one to work as expected too:

request = RequestFactory().get('/articles/4/')
view = MyMiddleware(MyView)
response = view(request, pk=4)

However this is not the case, since the middleware function expects only a single positional argument and not the keyword argument pk, thus raising a TypeError.

The attached files recommend a more flexible (albeit less simple) syntax and data flow for custom middleware that would prevent inexperienced developers from getting stuck here.

[Theodore Diamantidis]

Patch for documentation

[Nasir Hussain]

Replying to Theodore Diamantidis:
Should I create a PR with the patch in the documentation you provided?
I don't know what's the next steps if someone uploads a patch file too.

[Carlton Gibson]

This usage isn't correct:

view = MyMiddleware(MyView)

It treats views and middlewares as if they were equivalent, which they are not.

Django's BaseHandler provides a _get_response() method that uses the URLConf and URLResolver to determine the callback (i.e. view function) and parameters to pass to the view. (​django/core/handlers/base.py.)

It's this _get_response() that sits at the center of the Middleware Onion™. You can't just pass in a view.

To simulate the full dispatch you'd need to do something like this, as a minimum:

request = RequestFactory().get('/articles/4/')
def _get_response(request):
    return MyView(request, pk=4)
middleware_chain = MyMiddleware(_get_response)

(Lots of ways we might make that better...)

I've thought about adding something on this to the ​middleware usage guide but, by the time you're jumping through these hoops, I think the best advice is to use the provided test client and let Django handle the mapping between your middleware and views.