Cache interceptor in NestJS - Mini Project: Build & Apply

Cache Interceptor in NestJS

📖 Scenario: You are building a simple NestJS API that returns user data. To improve performance, you want to add caching so repeated requests return faster.

🎯 Goal: Build a NestJS cache interceptor that caches the response of a controller method.

📋 What You'll Learn

Create a cache interceptor class that implements NestInterceptor

Add a cache time-to-live (TTL) configuration variable

Use the cache manager to store and retrieve cached responses

Apply the cache interceptor to a controller method

💡 Why This Matters

🌍 Real World

Caching API responses improves performance and reduces server load in real-world web applications.

💼 Career

Understanding interceptors and caching is important for backend developers working with NestJS or similar frameworks.

1

Create the Cache Interceptor Class

Create a class called CacheInterceptor that implements NestInterceptor from @nestjs/common. Import Injectable and decorate the class with it.

NestJS

import { Injectable, NestInterceptor } from '@nestjs/common';

// Your code here

Need a hint?

Use implements NestInterceptor and decorate the class with @Injectable().

2

Add Cache TTL Configuration

Inside the CacheInterceptor class, add a private readonly property called ttl and set it to 30 (seconds).

NestJS

import { Injectable, NestInterceptor } from '@nestjs/common';

@Injectable()
export class CacheInterceptor implements NestInterceptor {
  private readonly ttl = 30;

  intercept(context, next) {
    // Your caching logic will go here
  }
}

// Your code here

Need a hint?

Declare private readonly ttl = 30; inside the class but outside the intercept method.

3

Implement Cache Logic in Intercept Method

In the intercept method, import ExecutionContext and CallHandler from @nestjs/common. Use next.handle() to get the response stream. For now, just return next.handle() without caching.

NestJS

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';

@Injectable()
export class CacheInterceptor implements NestInterceptor {
  private readonly ttl = 30;

  intercept(context: ExecutionContext, next: CallHandler) {
    // Return the response stream
    return next.handle();
  }
}

// Your code here

Need a hint?

Make sure to type the parameters as ExecutionContext and CallHandler, and return next.handle().

4

Apply Cache Interceptor to Controller Method

Create a controller class called UserController with a method getUser that returns a string 'User data'. Import and apply the CacheInterceptor to the getUser method using the @UseInterceptors(CacheInterceptor) decorator.

NestJS

import { Controller, Get, UseInterceptors } from '@nestjs/common';

@Controller('user')
export class UserController {
  @UseInterceptors(CacheInterceptor)
  @Get()
  getUser() {
    // Return user data string
  }
}

// Your code here

Need a hint?

Use @UseInterceptors(CacheInterceptor) above the getUser method and return the exact string 'User data'.