How to Use Middleware in Django: Syntax and Examples

In Django, middleware is a way to process requests and responses globally by creating a class with __init__, __call__, or specific methods like process_request. You add your middleware class path to the MIDDLEWARE list in settings.py to activate it.

Syntax

Django middleware is a class that can define methods to process requests and responses. The most common pattern is to define a __init__ method for setup and a __call__ method to handle the request and response.

Alternatively, you can define methods like process_request, process_view, process_response, and process_exception for specific hooks.

After creating the middleware class, add its full Python path to the MIDDLEWARE list in your Django settings.py file.

python

class SimpleMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        # Code before view
        response = self.get_response(request)
        # Code after view
        return response

Example

This example middleware adds a custom header to every HTTP response. It shows how to create the middleware class and enable it in settings.py.

python

class CustomHeaderMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        response = self.get_response(request)
        response['X-Custom-Header'] = 'Hello from middleware'
        return response

# In settings.py, add:
# MIDDLEWARE = [
#     ...
#     'yourapp.middleware.CustomHeaderMiddleware',
# ]

Output

When you make any HTTP request to your Django app, the response will include the header:
X-Custom-Header: Hello from middleware

Common Pitfalls

• Forgetting to add the middleware class path to the MIDDLEWARE list in settings.py means the middleware won't run.
• Not calling self.get_response(request) inside __call__ will block the request from reaching views.
• Modifying the request or response incorrectly can cause errors or unexpected behavior.

python

from django.http import HttpResponse

class BrokenMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        # Missing call to get_response blocks processing
        return HttpResponse('Blocked by middleware')

# Correct way:
class FixedMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        response = self.get_response(request)
        return response

Quick Reference

Middleware Hook	When It Runs	Purpose
__init__(self, get_response)	Once when server starts	Setup middleware instance
__call__(self, request)	For each request	Process request and response
process_request(self, request)	Before view	Modify request or return response early
process_view(self, request, view_func, view_args, view_kwargs)	Before view	Modify view or arguments
process_response(self, request, response)	After view	Modify response before sending
process_exception(self, request, exception)	If view raises exception	Handle exceptions

Key Takeaways

Middleware in Django is a class that processes requests and responses globally.

Always add your middleware class path to the MIDDLEWARE list in settings.py to activate it.

The __call__ method must call self.get_response(request) to continue processing.

Middleware can modify requests before views and responses after views.

Common mistakes include forgetting to add middleware or blocking requests by not calling get_response.