CacheModule setup in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when using CacheModule with default settings?

Consider a NestJS service that caches a value using CacheModule with default settings. What will be the behavior when retrieving a cached value immediately after setting it?

NestJS

import { CacheModule, Injectable, Module, Inject, CACHE_MANAGER } from '@nestjs/common';
import { Cache } from 'cache-manager';

@Injectable()
class SampleService {
  constructor(@Inject(CACHE_MANAGER) private cacheManager: Cache) {}

  async cacheValue() {
    await this.cacheManager.set('key', 'value');
    return await this.cacheManager.get('key');
  }
}

@Module({
  imports: [CacheModule.register()],
  providers: [SampleService],
})
export class AppModule {}

A The method returns 'value' as the cached data is immediately available.

B The method throws a runtime error because CacheModule requires explicit store configuration.

C The method returns undefined because caching is asynchronous and not ready yet.

D The method returns null because the default cache store does not store data.

💡 Hint

Think about how the default in-memory cache store works in NestJS CacheModule.

By default, CacheModule uses an in-memory store that immediately stores and retrieves data synchronously. So, setting and getting a value right after works as expected.

📝 Syntax

intermediate

Which CacheModule setup code is syntactically correct for setting a TTL of 5 seconds?

Choose the correct way to configure CacheModule with a time-to-live (TTL) of 5 seconds.

A CacheModule.register({ expire: 5 })

B CacheModule.register({ ttl: 5 })

C CacheModule.register({ timeToLive: 5 })

D CacheModule.register({ ttl: 5000 })

💡 Hint

Check the official CacheModule options for TTL property name and units.

The correct option uses 'ttl' in seconds. Option B uses milliseconds which is incorrect. Options C and D use invalid property names.

🔧 Debug

advanced

Why does this CacheModule setup cause a runtime error?

Examine the following CacheModule setup. Why will it cause a runtime error?

NestJS

import { CacheModule } from '@nestjs/common';

CacheModule.register({
  store: 'redis',
  host: 'localhost',
  port: 6379
});

A Because CacheModule does not support Redis caching.

B Because the 'host' and 'port' options are invalid for CacheModule.

C Because 'store' must be a function or a valid store instance, not a string.

D Because the CacheModule requires a 'ttl' option to be set.

💡 Hint

Think about how to properly configure a Redis cache store in NestJS CacheModule.

The 'store' option expects a function or a store instance, not a string. Using 'store: "redis"' causes a runtime error. You must import and pass the Redis store function.

❓ state_output

advanced

What is the value of 'cachedData' after this code runs?

Given this NestJS service using CacheModule, what will be the value of cachedData after fetchData() is called twice in a row?

NestJS

import { Injectable, Inject, CACHE_MANAGER } from '@nestjs/common';
import { Cache } from 'cache-manager';

@Injectable()
class DataService {
  constructor(@Inject(CACHE_MANAGER) private cacheManager: Cache) {}

  async fetchData() {
    const cached = await this.cacheManager.get('data');
    if (cached) return cached;
    const data = 'fresh data';
    await this.cacheManager.set('data', data, { ttl: 1 });
    return data;
  }
}

// Assume fetchData() is called twice within 2 seconds.

A 'fresh data' both times because TTL is 1 second and cache expires quickly.

B 'fresh data' first call, 'fresh data' second call because cache is still valid.

C undefined both times because cache is not set properly.

D 'fresh data' first call, undefined second call because cache is cleared.

💡 Hint

Consider the TTL of 1 second and the timing of calls.

The TTL is 1 second, so if the second call happens after 1 second, the cache expired and 'fresh data' is returned again. If calls happen within 1 second, second call would return cached data.

🧠 Conceptual

expert

Which statement about CacheModule global setup is true?

When configuring CacheModule globally in a NestJS app, which statement is correct?

A Setting <code>isGlobal: true</code> automatically enables Redis caching.

B CacheModule cannot be set globally; it must be imported in every module separately.

C Global CacheModule disables the ability to override cache settings in feature modules.

D Setting <code>isGlobal: true</code> in <code>CacheModule.register()</code> makes the cache available in all modules without importing it.

💡 Hint

Think about the purpose of the isGlobal option in NestJS modules.

Setting isGlobal: true in CacheModule.register() makes the cache service available app-wide without needing to import CacheModule in every module.