TTL configuration in NestJS

Introduction

TTL configuration helps you set how long data should live before it expires automatically. This keeps your app's data fresh and avoids clutter.

You want to cache API responses for a short time to improve speed.

You need to automatically remove old session data after some minutes.

You want to limit how long temporary tokens stay valid.

You want to clear outdated notifications after a set time.

You want to manage memory by deleting unused data automatically.

Syntax

NestJS

CacheModule.register({
  ttl: number_in_seconds
})

ttl means 'time to live' in seconds.

After this time, cached data is removed automatically.

Examples

Cache data expires after 60 seconds.

NestJS

CacheModule.register({ ttl: 60 })

Cache data never expires automatically.

NestJS

CacheModule.register({ ttl: 0 })

Cache data expires after 5 minutes (300 seconds).

NestJS

CacheModule.register({ ttl: 300 })

Sample Program

This example sets up a cache with a default TTL of 10 seconds. The setCache route stores a value with a 5-second TTL. The getCache route retrieves it. After 5 seconds, the cached value expires and returns a message.

NestJS

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

@Controller()
export class AppController {
  constructor(@Inject(CACHE_MANAGER) private cacheManager: Cache) {}

  @Get('set')
  async setCache() {
    await this.cacheManager.set('key', 'Hello TTL', { ttl: 5 });
    return 'Value cached with 5 seconds TTL';
  }

  @Get('get')
  async getCache() {
    const value = await this.cacheManager.get('key');
    return value ?? 'Cache expired or not set';
  }
}

@Module({
  imports: [CacheModule.register({ ttl: 10 })],
  controllers: [AppController],
})
export class AppModule {}

Important Notes

You can set TTL globally in CacheModule.register() or per item when setting cache.

TTL is in seconds, so 60 means one minute.

Setting TTL to 0 means the cache never expires automatically.

Summary

TTL controls how long cached data stays before automatic removal.

Use TTL to keep data fresh and save memory.

You can set TTL globally or per cached item.

Practice

1. What does TTL stand for in NestJS caching configuration?

easy

A. Timed Token Lock, a security feature for cache access

B. Time To Live, the duration cached data stays before removal

C. Temporary Transfer Lock, a pause on cache updates

D. Total Transaction Limit, the max number of cache writes

Solution

1. Step 1: Understand TTL meaning in caching

   TTL means how long cached data remains valid before it is removed automatically.

2. Step 2: Match TTL to the correct full form

   TTL stands for Time To Live, which fits the caching context perfectly.

3. Final Answer:

   Time To Live, the duration cached data stays before removal -> Option B

4. Quick Check:

   TTL = Time To Live [OK]

Hint: TTL means how long cache data lives before removal [OK]

Common Mistakes:

• Confusing TTL with security or transaction terms
• Thinking TTL is a cache size limit
• Assuming TTL is a manual cache clear command

2. Which is the correct way to set a global TTL of 10 seconds in NestJS cache module?

easy

A. CacheModule.register({ ttl: 10 })

B. CacheModule.register({ timeToLive: 10 })

C. CacheModule.register({ ttl: 10000 })

D. CacheModule.register({ expire: 10 })

Solution

1. Step 1: Identify TTL unit in NestJS cache config

   TTL is set in seconds, so 10 means 10 seconds.

2. Step 2: Check correct property name and value type

   The property is ttl, and the value is a number in seconds, so ttl: 10 is correct.

3. Final Answer:

   CacheModule.register({ ttl: 10 }) -> Option A

4. Quick Check:

   TTL in seconds uses 'ttl' property [OK]

Hint: TTL value is seconds, use 'ttl' property exactly [OK]

Common Mistakes:

• Using milliseconds instead of seconds
• Using wrong property names like timeToLive or expire
• Passing ttl as string instead of number

3. Given this NestJS cache config snippet:

CacheModule.register({ ttl: 5 })

What happens to cached data after 6 seconds?

medium

A. Cached data throws an error after 6 seconds

B. Cached data remains indefinitely until manually cleared

C. Cached data is refreshed automatically every 6 seconds

D. Cached data is automatically removed after 5 seconds

Solution

1. Step 1: Understand TTL effect on cached data

   TTL of 5 means cached data expires and is removed after 5 seconds.

2. Step 2: Check what happens after 6 seconds

   Since 6 seconds is more than 5, cached data is no longer valid and is removed.

3. Final Answer:

   Cached data is automatically removed after 5 seconds -> Option D

4. Quick Check:

   TTL 5 seconds means removal after 5 seconds [OK]

Hint: Data expires after TTL seconds, so 6 > 5 means removal [OK]

Common Mistakes:

• Thinking data stays forever without manual clear
• Assuming TTL refreshes cache automatically
• Believing cache throws errors on expiry

4. Identify the error in this NestJS cache TTL setup:

CacheModule.register({ ttl: '30' })

medium

A. TTL property name is incorrect, should be timeToLive

B. TTL cannot be set globally, only per item

C. TTL value should be a number, not a string

D. TTL value must be in milliseconds, not seconds

Solution

1. Step 1: Check TTL value type

   TTL expects a number representing seconds, but '30' is a string.

2. Step 2: Confirm correct property and units

   The property ttl is correct and uses seconds, so only the value type is wrong.

3. Final Answer:

   TTL value should be a number, not a string -> Option C

4. Quick Check:

   TTL must be numeric seconds, not string [OK]

Hint: TTL must be a number, not quoted string [OK]

Common Mistakes:

• Using string instead of number for TTL
• Changing property name incorrectly
• Confusing seconds with milliseconds

5. You want to cache user data with a TTL of 60 seconds, but override it to 120 seconds for admin users only. How do you configure TTL in NestJS?

hard

A. Set global TTL to 60, then use @CacheTTL(120) decorator on admin methods

B. Set global TTL to 120, then manually clear cache for non-admin users

C. Set TTL only in controller constructor based on user role

D. Use two separate CacheModules with different TTLs and switch dynamically

Solution

1. Step 1: Set global TTL for general users

   Configure CacheModule with ttl: 60 to cover normal users.

2. Step 2: Override TTL for admin users

   Use the @CacheTTL(120) decorator on admin-specific methods to extend TTL.

3. Final Answer:

   Set global TTL to 60, then use @CacheTTL(120) decorator on admin methods -> Option A

4. Quick Check:

   Global TTL + @CacheTTL override [OK]

Hint: Use global TTL plus @CacheTTL decorator for overrides [OK]

Common Mistakes:

• Trying to set TTL only in constructor without decorators
• Using multiple CacheModules unnecessarily
• Setting global TTL too high and clearing cache manually