Per-view caching in Django

Introduction

Per-view caching helps your website load faster by saving the result of a page so it doesn't have to be created again each time someone visits.

When you have a page that doesn't change often and is expensive to create.

When you want to reduce the load on your server during busy times.

When you want to speed up response time for users visiting the same page multiple times.

When you want to cache only specific pages instead of the whole site.

Syntax

Django

from django.views.decorators.cache import cache_page

@cache_page(timeout_in_seconds)
def my_view(request):
    # view code here
    return HttpResponse('content')

Use the @cache_page decorator above your view function to enable caching.

The timeout is how long the cached page stays saved before it refreshes.

Examples

This caches the homepage for 15 minutes (60 seconds * 15).

Django

from django.views.decorators.cache import cache_page

@cache_page(60 * 15)
def homepage(request):
    return HttpResponse('Welcome to the homepage!')

This caches the about page for 1 hour (3600 seconds).

Django

from django.views.decorators.cache import cache_page

@cache_page(3600)
def about(request):
    return HttpResponse('About us page')

A timeout of 0 means no caching is applied.

Django

from django.views.decorators.cache import cache_page

@cache_page(0)
def no_cache_view(request):
    return HttpResponse('No caching here')

Sample Program

This simple Django view returns a message and caches the page for 30 seconds. If you visit the page multiple times within 30 seconds, Django will serve the saved page instead of running the view again.

Django

from django.http import HttpResponse
from django.views.decorators.cache import cache_page

@cache_page(30)
def hello_view(request):
    return HttpResponse('Hello, this page is cached for 30 seconds!')

Important Notes

Remember to import cache_page from django.views.decorators.cache.

Per-view caching works best for pages that do not change for all users.

To clear the cache manually, you may need to restart your server or use cache backend commands.

Summary

Per-view caching saves the output of a view to speed up repeated visits.

Use the @cache_page(timeout) decorator to enable it.

Choose a timeout that fits how often your page content changes.

Practice

1. What is the main purpose of using @cache_page(timeout) in Django views?

easy

A. To connect the view to the database

B. To save the view's output and speed up repeated visits

C. To validate user input before processing

D. To handle user authentication automatically

Solution

1. Step 1: Understand what caching does

   Caching stores the output of a view so it can be reused without recalculating.

2. Step 2: Recognize the role of @cache_page(timeout)

   This decorator saves the rendered page for the given timeout to speed up future requests.

3. Final Answer:

   To save the view's output and speed up repeated visits -> Option B

4. Quick Check:

   Per-view caching = save output for speed [OK]

Hint: Caching saves page output to speed up repeated visits [OK]

Common Mistakes:

• Thinking it validates input
• Confusing caching with authentication
• Assuming it connects to the database

2. Which of the following is the correct way to apply per-view caching with a 5-minute timeout in Django?

easy

A. @cache_page('300')
def my_view(request):
pass

B. @cache_page(5)
def my_view(request):
pass

C. @cache_page(timeout=5)
def my_view(request):
pass

D. @cache_page(300)
def my_view(request):
pass

Solution

1. Step 1: Understand the timeout parameter

   The timeout is in seconds, so 5 minutes = 300 seconds.

2. Step 2: Check correct syntax for @cache_page

   The decorator takes an integer timeout in seconds without quotes.

3. Final Answer:

   @cache_page(300)\ndef my_view(request):\n pass -> Option D

4. Quick Check:

   Timeout in seconds, no quotes = @cache_page(300) def my_view(request): pass [OK]

Hint: Timeout is seconds as integer, no quotes [OK]

Common Mistakes:

• Using string '300' instead of integer
• Passing timeout as minutes instead of seconds
• Using keyword argument timeout incorrectly

3. Given this Django view with per-view caching:

@cache_page(60)
def home(request):
    return HttpResponse(str(time.time()))

What will happen if you refresh the page multiple times within 60 seconds?

medium

A. The page shows the same timestamp for 60 seconds

B. The page shows a new timestamp on every refresh

C. The page raises an error because time.time() is not cached

D. The page shows timestamps increasing by 60 seconds

Solution

1. Step 1: Understand what @cache_page(60) does

   It caches the entire response for 60 seconds.

2. Step 2: Analyze the effect on time.time()

   Since the response is cached, the timestamp won't update until cache expires.

3. Final Answer:

   The page shows the same timestamp for 60 seconds -> Option A

4. Quick Check:

   Cache holds output unchanged for timeout [OK]

Hint: Cached view returns same output until timeout expires [OK]

Common Mistakes:

• Expecting timestamp to update every refresh
• Thinking caching only affects database queries
• Assuming cache raises errors with dynamic content

4. You wrote this Django view with caching:

from django.views.decorators.cache import cache_page

@cache_page('60')
def about(request):
    return HttpResponse('About page')

Why does this code cause an error?

medium

A. The timeout value is a string instead of an integer

B. The decorator is missing parentheses

C. The view function must be a class-based view

D. The import statement is incorrect

Solution

1. Step 1: Check the timeout argument type

   The timeout must be an integer number of seconds, not a string.

2. Step 2: Identify the error cause

   Passing '60' as a string causes a TypeError in the decorator.

3. Final Answer:

   The timeout value is a string instead of an integer -> Option A

4. Quick Check:

   Timeout must be int, not string [OK]

Hint: Timeout must be integer, not string [OK]

Common Mistakes:

• Using quotes around timeout number
• Forgetting parentheses on decorator
• Thinking function type matters here

5. You want to cache a Django view that shows user-specific data but still use per-view caching. Which approach correctly applies caching without showing wrong data to users?

hard

A. Cache the view globally and add user ID in the URL to separate cache keys

B. Use @cache_page(120) without changes; caching will separate users automatically

C. Use @cache_page(120) and add Vary: Cookie header to cache per user session

D. Do not use caching on user-specific views at all

Solution

1. Step 1: Understand caching user-specific data risks

   Global caching can show one user's data to others if not separated.

2. Step 2: Use Vary header to separate cache by user session

   Adding Vary: Cookie tells cache to store different versions per user session cookie.

3. Final Answer:

   Use @cache_page(120) and add Vary: Cookie header to cache per user session -> Option C

4. Quick Check:

   Vary header separates cache by user [OK]

Hint: Use Vary header to separate cache per user [OK]

Common Mistakes:

• Assuming caching separates users automatically
• Avoiding caching user views unnecessarily
• Adding user ID in URL without proper cache keys