How to implement a custom caching strategy for API responses in a Nest.js application

Implementing a custom caching strategy for API responses in a Nest.js application involves creating a middleware or an interceptor to intercept incoming requests, check if the response is cached, and cache the response if it's not already cached. Here's how you can achieve this:

1. Choose a Caching Library:

   Before implementing the caching strategy, choose a caching library that suits your needs. Some popular caching libraries in the Node.js ecosystem are node-cache, memory-cache, redis, etc. For this example, let's use node-cache.

   First, install the node-cache library:

   bashCopy code
   npm install node-cache
   

2. Create a Custom Caching Middleware or Interceptor:

   Create a middleware or interceptor that intercepts incoming requests, checks if the response is cached, and caches the response if necessary.

   typescriptCopy code
   // cache.middleware.ts
   
   import { Injectable, NestMiddleware, HttpException, HttpStatus } from '@nestjs/common';
   import { Request, Response } from 'express';
   import NodeCache from 'node-cache';
   
   const cache = new NodeCache();
   
   @Injectable()
   export class CacheMiddleware implements NestMiddleware {
       use(req: Request, res: Response, next: () => void) {
           const cacheKey = req.originalUrl || req.url;
           const cachedResponse = cache.get(cacheKey);
   
           if (cachedResponse) {
               console.log('Response retrieved from cache');
               return res.status(HttpStatus.OK).json(cachedResponse);
           }
   
           const originalSend = res.send;
           res.send = function (body) {
               if (res.statusCode === HttpStatus.OK) {
                   cache.set(cacheKey, body, /* TTL */ 60); // Cache response for 60 seconds (adjust TTL as needed)
                   console.log('Response cached');
               }
               originalSend.call(this, body);
           };
   
           next();
       }
   }
   

   In this middleware, we're using node-cache to cache responses. Adjust the caching mechanism and configuration (e.g., TTL) according to your requirements.

3. Register the Middleware:

   Register the CacheMiddleware in your Nest.js module to apply it to incoming requests.

   typescriptCopy code
   // app.module.ts
   
   import { Module, NestModule, MiddlewareConsumer } from '@nestjs/common';
   import { CacheMiddleware } from './cache.middleware';
   
   @Module({})
   export class AppModule implements NestModule {
       configure(consumer: MiddlewareConsumer) {
           consumer.apply(CacheMiddleware).forRoutes('*');
       }
   }
   

   In this example, the middleware is applied to all routes (*). You can specify specific routes or controllers where you want the middleware to be applied.

4. Use the Cached Responses:

   With the middleware in place, responses will be cached automatically for subsequent requests.

   typescriptCopy code
   import { Controller, Get } from '@nestjs/common';
   
   @Controller('data')
   export class DataController {
       @Get()
       getData() {
           // Fetch data from database or external API
           return { message: 'Data fetched' };
       }
   }
   

   Responses from the getData() method in your controllers will be cached by the middleware.

With this setup, responses from your API endpoints will be cached according to the caching strategy implemented in the middleware. Adjust the caching logic and configuration according to your specific requirements.