TTL configuration in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a TTL of 60 seconds in the cache manager options.

NestJS

CacheModule.register({ ttl: [1] })

Drag options to blanks, or click blank then click option'

A-1

B60

C0

D6000

Attempts:

3 left

💡 Hint

Common Mistakes

Using milliseconds instead of seconds.

Setting TTL to 0 which disables expiration.

The ttl option sets the time-to-live in seconds. Here, 60 means cache entries expire after 60 seconds.

2fill in blank

medium

Complete the code to inject the cache manager service in a NestJS service constructor.

NestJS

constructor(@Inject(CACHE_MANAGER) private [1]: Cache) {}

Drag options to blanks, or click blank then click option'

AcacheClient

BcacheService

Ccache

DcacheManager

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that does not match the injected token.

Forgetting to mark the variable as private.

The injected variable name is commonly cacheManager to represent the cache service instance.

3fill in blank

hard

Fix the error in setting a TTL for a specific cache key using the cache manager's set method.

NestJS

await this.cacheManager.set('user_123', userData, [1]);

Drag options to blanks, or click blank then click option'

A{ ttl: 60 }

B60000

C60

D{ ttl: 60000 }

Attempts:

3 left

💡 Hint

Common Mistakes

Passing TTL as a raw number instead of an options object.

Confusing seconds and milliseconds units.

The set method expects the TTL option as an object with a ttl property in seconds. Here, { ttl: 60 } sets TTL to 60 seconds.

4fill in blank

hard

Fill both blanks to configure the cache module with a TTL of 120 seconds and a max cache size of 100 items.

NestJS

CacheModule.register({ ttl: [1], max: [2] })

Drag options to blanks, or click blank then click option'

A120

B60

C100

D200

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up TTL and max values.

Using TTL in milliseconds instead of seconds.

The ttl is set to 120 seconds for cache expiration, and max limits the cache size to 100 items.

5fill in blank

hard

Fill all three blanks to create a cache key with a prefix, set a TTL of 30 seconds, and store the value using the cache manager.

NestJS

const key = `session:[1]`;
await this.cacheManager.set(key, [2], { ttl: [3] });

Drag options to blanks, or click blank then click option'

AuserId

BsessionData

C30

DuserToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong variable for the key or value.

Setting TTL as a string instead of a number.

The key uses a prefix session: plus the userId. The value stored is sessionData with a TTL of 30 seconds.

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