Liam Li | Caching with Django REST Framework

In the realm of web development, particularly in backend services development using Django, caching emerges as a pivotal component. Today, we delve into this critical feature, focusing on its implementation in Django REST Framework (DRF). Caching stands as a key strategy, enhancing application performance and contributing significantly to efficient user experiences and system scalability.

What is Caching?

Caching is like a superpower for web applications. It's about storing parts of your website (like data or pages) in a temporary storage area, known as a cache. This process makes future requests for that data lightning-fast because the information is retrieved from the cache instead of going through the time-consuming process of fetching it from the main database. It's like having a super-fast shortcut to the data you need most!

Why Use Caching?

Imagine you run a website that gets thousands of visits per day. Without caching, each visit might mean querying your database for information, which can slow down your site and make your users wait (and we definitely don't want that!). With caching, frequently requested data is readily available, making your site zippy and efficient. It's all about enhancing user experience and reducing server load - a win-win!

Configuring Caching in Django

Django provides a ready-to-use caching framework that abstracts cache operations, offering a unified interface for reading and writing cache data. Regardless of the underlying cache service (like Redis, Memcached, or file system), the upper layer application has the same logic and interface for cache operations.

Choosing a Cache Service

The key to configuring Django cache is choosing a cache service. In our project, we use Local Memory cache in the development environment and Redis cache in the production environment.

Development Environment Configuration

For local memory cache service in the development environment, add the following to settings/local.py:

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
    }
}

Production Environment Configuration

For Redis cache in the production environment, first, install django-redis-cache:

$ pipenv install django-redis-cache

Then, add the following configuration to settings/production.py:

CACHES = {
    "default": {
        "BACKEND": "redis_cache.RedisCache",
        "LOCATION": "redis://:password@host:port/db",
        "OPTIONS": {
            "CONNECTION_POOL_CLASS": "redis.BlockingConnectionPool",
            "CONNECTION_POOL_CLASS_KWARGS": {"max_connections": 50, "timeout": 20},
            "MAX_CONNECTIONS": 1000,
            "PICKLE_VERSION": -1,
        },
    },
}

Refer to the tutorial's Redis service section for starting the Redis service.

Two Primary Methods of Caching in DRF

When it comes to caching in Django REST Framework, there are two main approaches:

Using Django's Native Caching: This method leverages Django's built-in caching mechanisms. It's straightforward and can be implemented with minimal configuration, ideal for simple caching needs.
Using drf-extensions for Advanced Caching: This is a more sophisticated approach that provides enhanced capabilities beyond Django's native caching.

Advantages of Using drf-extensions

drf-extensions is an advanced encapsulation of Django's native caching, offering several benefits:

Flexibility in Cache Key Generation: With drf-extensions, you can create complex cache keys using KeyConstructor and KeyBit, which is essential for scenarios where the URL alone isn't enough to uniquely identify a cache entry.
Specialized Caching Decorators and Mixins: It provides specialized decorators like cache_response and mixins for different caching scenarios, such as ListCacheResponseMixin and RetrieveCacheResponseMixin, which streamline the process of adding caching to your views and viewsets.

Caching in DRF: A Perfect Match

Now, let's talk about the Django REST Framework (DRF), a powerful toolkit for building Web APIs. DRF and caching are like peanut butter and jelly - they just go perfectly together. By integrating caching in DRF, we ensure our API responses are fast and responsive, improving both backend efficiency and frontend performance.

What is `drf-extensions`?

drf-extensions is a modular extension for Django REST Framework (DRF), designed to enhance its capabilities with additional features and utilities. This module acts as an advanced toolkit that simplifies and enriches the development of DRF-based applications. It includes a variety of functionalities like extended viewsets, decorators, and mixins, which enable more efficient and flexible API design. Key features include advanced caching mechanisms, nested routes, and additional response mixins, allowing developers to build more complex, efficient, and scalable web APIs with less effort. By extending the core functionality of DRF, drf-extensions makes it easier to implement custom behavior and optimize API performance, making it a valuable asset for developers working with Django REST Framework.

What Does `drf-extensions` Offer for Caching?

So, what specific functions and classes does drf-extensions provide for caching? Here are the key elements we'll be using:

KeyConstructor

This can be understood as a cache key generation class. Let's delve into the logic of API interface caching with this pseudocode:

Given a URL, try to find the response result of this URL interface from the cache:

if result in cache:
    return result from cache
else:
    generate response result
    store response result in cache (for next query)
    return generated response result

Cache results are stored as key-value pairs. The crucial part here is generating a corresponding key when storing or querying cache results. For instance, we can use the API request URL as the cache key, ensuring the same interface request returns the same cache content. However, in more complex scenarios, using the URL as the key is insufficient. For example, authenticated and unauthenticated users may receive different results for the same API request. Hence, drf-extensions uses the KeyConstructor base class to provide a flexible way of generating keys.

KeyBit

This can be understood as a specific rule definition within the key generation rules defined by KeyConstructor. For example, in the same API request, authenticated and unauthenticated users will receive different responses. We can define the key generation rule as the request's URL + the user's authentication ID. In this case, the URL can be seen as one KeyBit, and the user ID is another KeyBit.

cache_response Decorator

This decorator is used to decorate views in Django REST Framework (individual view functions, actions within viewsets, etc.). Views decorated with this will have caching functionality.

How to Implement Caching in DRF with drf-extensions?

1. Getting Started with `drf-extensions`

First things first, let's set up caching in DRF using the drf-extensions package. This package extends DRF's capabilities, making it a breeze to add caching.

$ pip install drf-extensions

2. Decorating Our Views

In the heart of our DRF project, we use decorators like cache_response to sprinkle some caching magic on our views. It's like telling our views, "Hey, keep this data handy for next time!"

from rest_framework_extensions.cache.decorators import cache_response

class BlogPostView(views.APIView):
    @cache_response()
    def get(self, request, *args, **kwargs):
        # Imagine fetching and returning a list of delightful blog posts here

3. Harnessing Extension Classes

DRF-extensions offer three fabulous extension classes for different caching needs:

ListCacheResponseMixin: Perfect for when you want to cache a list of items.
RetrieveCacheResponseMixin: Ideal for caching details of a single item.
CacheResponseMixin: The all-in-one solution for both list and detail views.

These mixins add caching to our viewsets with minimal fuss, keeping our code clean and our application fast.

Let's look at some concrete examples:

Using ListCacheResponseMixin

When you want to cache a list of items, such as a list of blog posts, you can use ListCacheResponseMixin. Here's a quick example:

from rest_framework_extensions.cache.mixins import ListCacheResponseMixin
from rest_framework import viewsets
from .models import BlogPost
from .serializers import BlogPostSerializer

class BlogPostListViewSet(ListCacheResponseMixin, viewsets.ReadOnlyModelViewSet):
    queryset = BlogPost.objects.all()
    serializer_class = BlogPostSerializer

This mixin automatically caches the response of the list view, making subsequent requests much faster.

Using RetrieveCacheResponseMixin

For caching the details of a single item, like the details of a specific blog post, you can use RetrieveCacheResponseMixin:

from rest_framework_extensions.cache.mixins import RetrieveCacheResponseMixin

class BlogPostDetailViewSet(RetrieveCacheResponseMixin, viewsets.ReadOnlyModelViewSet):
    queryset = BlogPost.objects.all()
    serializer_class = BlogPostSerializer
    lookup_field = 'slug'  # Assuming each blog post has a unique slug

This will cache the response for individual blog post detail views.

Using CacheResponseMixin

If you have a viewset that needs both list and detail view caching, CacheResponseMixin is your go-to choice:

from rest_framework_extensions.cache.mixins import CacheResponseMixin

class BlogPostViewSet(CacheResponseMixin, viewsets.ModelViewSet):
    queryset = BlogPost.objects.all()
    serializer_class = BlogPostSerializer
    lookup_field = 'slug'

Here, both list and detail views of the BlogPostViewSet are cached, providing an efficient retrieval of data.

4. Setting Up Our Cache Strategy

Lastly, we tailor our cache settings in the configuration file. This step is like setting the stage for how and where we store our cached data.

# DRF Extensions Settings

REST_FRAMEWORK_EXTENSIONS = {
    'DEFAULT_CACHE_RESPONSE_TIMEOUT': 60 * 60,  # Cache duration in seconds
    'DEFAULT_USE_CACHE': 'default',  # Or 'redis', for the Redis adventurers
}

Conclusion

By embracing caching in DRF, we not only make our applications snappy and efficient but also ensure a delightful experience for our users. It's about making our web applications not just good, but great. So, let's cache in on this fantastic feature and watch our applications soar!

Caching with Django REST Framework