How to write a custom Django Middleware

Posted on Sun 23 August 2015 in Development • Tagged with Django, HowTo, middleware, Python, tutorial

To understand how a Django Middleware works we need to remember that the basic architecture of Django is composed by a request and a response. A middleware is something that stays in the middle. Let's give a look to the next diagram, taken from official Django documentation:

middleware

Important things to know

There are four important things to know about middlewares:

  • You need to write a class that just inherit from object
  • The order where you place your middleware in settings.py is important: middlewares are processed from top to bottom during a request and from bottom to top during a response.
  • You don't need to implement all the available methods of a middleware. For example you can just implement process_request and process_template_response
  • If you implement process_request and you decide to return an HttpResponse, all the other middlewares, views etc... will be ignored and only your response will be returned

Writing a middleware

In my example I wanted to implement a feature that saves the time when a request is made and the time when a request has been processed, then calculates the time delta and exposes this value in the context so that is accessible from our templates. How to implement a similar feature using a middleware? Here is my example:

from datetime import datetime


class BenchmarkMiddleware(object):
    def process_request(self, request):
        request._request_time = datetime.now()

    def process_template_response(self, request, response):
        response_time = request._request_time - datetime.now()
        response.context_data['response_time'] = abs(response_time)
        return response

Please don't care about how I calculated the time. I'm aware that there are better ways to do it, but I just wanted to keep it simple and show how to implement a simple middleware.

If you want to see a complete example of a project that includes and uses this middleware, here you can find the complete source code: https://github.com/andreagrandi/benchmark-middleware-example

References