Nathan Ostgard

When I have Django URL patterns like:

urlpatterns = patterns('',
  (r'^(?P<foo_id>\w+)/$', 'myproject.myapp.views.show'),
  (r'^(?P<foo_id>\w+)/edit/$', 'myproject.myapp.views.edit'),
  (r'^(?P<foo_id>\w+)/delete/$', 'myproject.myapp.views.delete'),
)

I always end up with views like:

def show(self, foo_id):
  foo = get_object_or_404(Foo, id=foo_id)
  ...

def edit(self, foo_id):
  foo = get_object_or_404(Foo, id=foo_id)
  ...

def delete(self, foo_id):
  foo = get_object_or_404(Foo, id=foo_id)
  ...

Having the same few lines at the top of every function in makes me feel dirty. You can clean this up with a Middleware class, replacing foo_id with the actual object before calling the view.

myproject/myapp/middleware.py looks like this:

from django.shortcuts import get_object_or_404
from someapp.models import Foo

class FindObjects:
  def process_view(self, request, view_func, view_args, view_kwargs):
    if 'foo_id' in view_kwargs:
      view_kwargs['foo'] = get_object_or_404(Foo, id=view_kwargs['foo_id'])
      del view_kwargs['foo_id']

I include it in settings.py:

MIDDLEWARE_CLASSES = (
  ...
  'myproject.myapp.middleware.FindObjects',
)

And now my views look like this:

def show(request, foo):
  ... yay! do stuff with foo! ...

Very useful for views with many parameters, or views with multiple optional parameters. In one project, I have views which process data for three different situations: data in a metropolitan area, data in a city, or data in a city within a metro. My middleware for that looks like this:

from django.shortcuts import get_object_or_404
from phuce.metros.models import City, Metro

class FindObjects:
  def process_view(self, request, view_func, view_args, view_kwargs):
    city = metro = None
    if 'metro_link' in view_kwargs:
      metro = get_object_or_404(Metro, link=view_kwargs['metro_link'])
      del view_kwargs['metro_link']
      view_kwargs['metro'] = metro
    if 'city_link' in view_kwargs:
      if metro:
        city = get_object_or_404(City, metro=metro, \
                                 metro_link=view_kwargs['city_link'])
      else:
        city = get_object_or_404(City, link=view_kwargs['city_link'])
      del view_kwargs['city_link']
      view_kwargs['city'] = city

It’s much tidier without that monster in my views.