Accessing the current view class instance in Django middleware - django

Question

Question:
I'm trying to access an attribute of the view instance in the middleware layer.
For example, given a class-based view like this:
# views.py
class MyView(View):
my_attribute = 'something'
I'd love to be able to get a handle on my_attribute in the middleware by doing something like this:
# middleware.py
def process_view(self, request, view_func, view_args, view_kwargs):
my_attribute = request.view.my_attribute
Of course, this does not work because Django doesn't expose the view instance through the request object. Is there a way to get this accomplished?
Thanks!
My first attempt:
I initially figured that the process_view() method might be a good place to do this. Unfortunately, the view_func argument it receives contains a function -- the output of MyView.as_view() -- rather than the view instance itself. From the Django docs:
process_view(self, request, view_func, view_args, view_kwargs)
...view_func is the Python function that Django is about to use. (It’s the actual function
object, not the name of the function as a string.)...
My second attempt:
A handle to the view instance is available in process_template_response() method, but it's pretty awkward, and, in any case, I'd like to be able to work with my_attribute at an earlier point in the middleware stack. But this does work:
def process_template_response(self, request, response):
my_attribute = response.context_data['view'].my_attribute

Answer 1

There is no built-in way to do this, but here is a solution given to me by a kindly user on the django-users mailing list. I'm reposting his suggestion here in case anyone else is trying to do the same thing.
This is useful if:
you want to identify properties of the current view in your middleware and perform processing accordingly, and;
for various reasons you don't want to use mixins or decorators to accomplish similar results.
This inspects the view_func object passed to the process_view() middleware hook and determines and imports the the appropriate view class.
# middleware.py
from myutils import get_class
def process_view(self, request, view_func, view_args, view_kwargs):
view = get_class(view_func.__module__, view_func.__name__)
view.my_attribute
Then your get_class() definition:
# myutils.py
from django.utils import importlib
def get_class(module_name, cls_name):
try:
module = importlib.import_module(module_name)
except ImportError:
raise ImportError('Invalid class path: {}'.format(module_name))
try:
cls = getattr(module, cls_name)
except AttributeError:
raise ImportError('Invalid class name: {}'.format(cls_name))
else:
return cls

Answer 2

Using decorators, there are quite some ways to achieve the desired behavior.
1. If you only want to mark a class for the middleware to do something
from django.utils.decorators import classonlymethod
def special_marker(class_view):
def as_view(cls, **initkwargs):
view = super(cls, cls).as_view(**initkwargs)
view.special_marker = True
return view
return type(class_view.__name__, (class_view,), {
'as_view': classonlymethod(as_view),
})
#special_marker
class MyView(View):
pass
class MyMiddleware:
def __init__(self, get_response):
self.get_response = get_response
def __call__(self, request):
return self.get_response(request)
def process_view(self, request, view_func, view_args, view_kwargs):
special_marker = getattr(view_func, 'special_marker', False)
if special_marker:
# Do something
2. If you want to pass some data to the middleware that you don't need in the view
from django.utils.decorators import classonlymethod
def tell_middleware(**kwargs):
def wrapper(class_view):
def as_view(cls, **initkwargs):
view = super(cls, cls).as_view(**initkwargs)
for k, v in kwargs.items():
setattr(view, k, v)
return view
return type(class_view.__name__, (class_view,), {
'as_view': classonlymethod(as_view),
})
return wrapper
#tell_middleware(my_attribute='something')
class MyView(View):
pass
class MyMiddleware:
def __init__(self, get_response):
self.get_response = get_response
def __call__(self, request):
return self.get_response(request)
def process_view(self, request, view_func, view_args, view_kwargs):
my_attribute = getattr(view_func, 'my_attribute', 'default value')
if my_attribute == 'something':
# Do something
3. If you want to expose some view attributes to the middleware
from django.utils.decorators import classonlymethod
def expose_to_middleware(*args):
def wrapper(class_view):
def as_view(cls, **initkwargs):
view = super(cls, cls).as_view(**initkwargs)
for attr in args:
setattr(view, attr, getattr(class_view, attr)
return view
return type(class_view.__name__, (class_view,), {
'as_view': classonlymethod(as_view),
})
return wrapper
#expose_to_middleware('my_attribute', 'my_other_attribute')
class MyView(View):
my_attribute = 'something'
my_other_attribute = 'else'
unexposed_attribute = 'foobar'
class MyMiddleware:
def __init__(self, get_response):
self.get_response = get_response
def __call__(self, request):
return self.get_response(request)
def process_view(self, request, view_func, view_args, view_kwargs):
my_attribute = getattr(view_func, 'my_attribute', 'default value')
if my_attribute == 'something':
# Do something

Answer 3

Another solution could be to create a new View class:
from django.views.generic.base import View
class AddClassView(View):
#classonlymethod
def as_view(cls, **initkwargs):
view = super(AddClassView, cls).as_view(**initkwargs)
view.cls = cls
return view
And use this in your class based view:
# views.py
class MyView(AddClassView):
my_attribute = 'something'
Then you do the following in the middleware:
# middleware.py
def process_view(self, request, view_func, view_args, view_kwargs):
view_func.cls.my_attribute # 'something'
This method is used in the Django REST Framework(https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/views.py#L94-L104)

Answer 4

If it depends on the view, it should probably be a mixin of that view. If you're doing something like a menu that depends on the active view, I'd do a reverse lookup of the current URL name:
see a previous answer about using URL name lookup of the current URL