Cache tags in Laravel - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when retrieving a tagged cache item after flushing one tag?

Consider the following Laravel cache code:

Cache::tags(['users', 'settings'])->put('config', 'value1', 3600);
Cache::tags(['users'])->flush();
$value = Cache::tags(['users', 'settings'])->get('config');
echo $value ?? 'null';

What will be printed?

Laravel

Cache::tags(['users', 'settings'])->put('config', 'value1', 3600);
Cache::tags(['users'])->flush();
$value = Cache::tags(['users', 'settings'])->get('config');
echo $value ?? 'null';

A value1

B false

C null

D Throws an exception

💡 Hint

Think about what happens when you flush a tag and how it affects cache items with multiple tags.

Flushing the 'users' tag removes all cache items tagged with 'users', including those tagged with both 'users' and 'settings'. So the item 'config' is removed and returns null.

📝 Syntax

intermediate

Which option correctly stores a value with multiple cache tags in Laravel?

Which of the following code snippets correctly stores the value 'blue' with tags 'colors' and 'themes' for 10 minutes?

A Cache::tags('colors')->tags('themes')->put('background', 'blue', 600);

B Cache::tags(['colors', 'themes'])->put('background', 'blue', 600);

C Cache::tags(['colors'], ['themes'])->put('background', 'blue', 600);

D Cache::tags('colors', 'themes')->put('background', 'blue', 600);

💡 Hint

Remember how to pass multiple tags as an array in Laravel's cache tagging.

The tags method accepts an array of tags. Chaining multiple calls or passing array of arrays is incorrect.

🔧 Debug

advanced

Why does this tagged cache retrieval return null unexpectedly?

Given this code:

Cache::tags(['session', 'user'])->put('token', 'abc123', 300);
// ... some time later
$token = Cache::tags(['user', 'session'])->get('token');
echo $token ?? 'null';

The output is 'null'. Why?

Laravel

Cache::tags(['session', 'user'])->put('token', 'abc123', 300);
$token = Cache::tags(['user', 'session'])->get('token');
echo $token ?? 'null';

A Cache tags order matters; ['user', 'session'] is different from ['session', 'user']

B The cache key 'token' was never stored

C Cache tags are case-sensitive and tags differ in case

D The cache store does not support tagging

💡 Hint

Notice that the order of the tags is reversed between put and get.

Cache tags order matters because the tags array is serialized to compute the tag root key hash. Different order produces different prefix for the item key, so retrieval fails.

❓ state_output

advanced

What is the number of items in cache after flushing one tag?

Consider these cache operations:

Cache::tags(['a', 'b'])->put('item1', 'x', 100);
Cache::tags(['a'])->put('item2', 'y', 100);
Cache::tags(['b'])->put('item3', 'z', 100);
Cache::tags(['a'])->flush();
$count = Cache::tags(['b'])->getMultiple(['item1', 'item3']);
$itemsCount = count(array_filter($count));
echo $itemsCount;

What number is printed?

Laravel

Cache::tags(['a', 'b'])->put('item1', 'x', 100);
Cache::tags(['a'])->put('item2', 'y', 100);
Cache::tags(['b'])->put('item3', 'z', 100);
Cache::tags(['a'])->flush();
$count = Cache::tags(['b'])->getMultiple(['item1', 'item3']);
$itemsCount = count(array_filter($count));
echo $itemsCount;

A 3

B 2

C 0

D 1

💡 Hint

Think about which items are removed when flushing tag 'a' and which remain under tag 'b'.

Flushing tag 'a' removes items tagged with 'a'. 'item1' has tags 'a' and 'b' so it is removed. 'item2' has 'a' only, removed. 'item3' has 'b' only, remains. So only 'item3' is returned.

🧠 Conceptual

expert

Which statement about Laravel cache tags is true?

Choose the correct statement about Laravel cache tags:

A Cache tags allow grouping cache items so flushing one tag removes only items with that tag, even if they have multiple tags.

B Cache tags require the cache key to be unique across all tags to avoid collisions.

C Cache tags can be nested to create hierarchical cache groups automatically.

D Cache tags are supported by all Laravel cache drivers including 'file' and 'database'.

💡 Hint

Think about how flushing a tag affects items with multiple tags and driver support.

Flushing a tag removes all items with that tag, even if they have other tags. Not all drivers support tags (e.g., file, database). Tags are flat, not hierarchical. Cache keys can be reused under different tags.

Practice

1. What is the main purpose of using cache tags in Laravel?

easy

A. To group cached items for easy management and selective clearing

B. To encrypt cached data automatically

C. To increase cache storage size

D. To log cache hits and misses

Solution

1. Step 1: Understand cache tags concept

   Cache tags allow grouping of cached items under one or more tags.

2. Step 2: Identify the benefit of grouping

   This grouping helps to clear or manage all related cache items easily by tag.

3. Final Answer:

   To group cached items for easy management and selective clearing -> Option A

4. Quick Check:

   Cache tags = group and manage cache [OK]

Hint: Cache tags group items for easy clearing [OK]

Common Mistakes:

• Thinking tags encrypt data
• Assuming tags increase cache size
• Confusing tags with logging features

2. Which of the following is the correct syntax to store a cache item with a tag in Laravel?

easy

A. Cache::tags('users')->put('user_1', 'John', 3600);

B. Cache::put('user_1', 'John')->tags(['users'], 3600);

C. Cache::put('user_1', 'John', 3600)->tags(['users']);

D. Cache::tags(['users'])->put('user_1', 'John', 3600);

Solution

1. Step 1: Recall Laravel cache tag syntax

   The tags() method accepts an array of tags before calling put().

2. Step 2: Check method chaining order

   The correct order is Cache::tags([...])->put(key, value, time).

3. Final Answer:

   Cache::tags(['users'])->put('user_1', 'John', 3600); -> Option D

4. Quick Check:

   tags() before put() with array [OK]

Hint: Use tags() with array before put() [OK]

Common Mistakes:

• Passing tags after put()
• Using string instead of array in tags()
• Chaining methods in wrong order

3. Given the code below, what will be the output of Cache::tags(['products'])->get('item_1'); after Cache::tags(['products'])->flush(); is called?

Cache::tags(['products'])->put('item_1', 'Book', 600);
Cache::tags(['products'])->flush();
$value = Cache::tags(['products'])->get('item_1');
echo $value ?? 'Not found';

medium

A. Not found

B. CacheException

C. null

D. Book

Solution

1. Step 1: Understand flush() effect on tagged cache

   Calling flush() on a tag clears all cached items under that tag.

2. Step 2: Check retrieval after flush

   After flushing, get('item_1') returns null, so the null coalescing operator outputs 'Not found'.

3. Final Answer:

   Not found -> Option A

4. Quick Check:

   flush() clears tagged cache = 'Not found' [OK]

Hint: flush() clears all tagged cache items [OK]

Common Mistakes:

• Expecting cached value after flush
• Confusing flush() with forget()
• Assuming flush() only clears one item

4. Identify the error in the following Laravel cache tag usage:

Cache::tags('sessions')->put('session_1', 'data', 120);
Cache::tags(['sessions'])->flush();

medium

A. Missing cache driver configuration

B. Using string instead of array in tags() method

C. Calling flush() on tags is not allowed

D. put() method requires a closure

Solution

1. Step 1: Check tags() method argument type

   The tags() method requires an array of tags, not a string.

2. Step 2: Identify the incorrect usage

   Passing a string 'sessions' instead of ['sessions'] causes an error.

3. Final Answer:

   Using string instead of array in tags() method -> Option B

4. Quick Check:

   tags() needs array, not string [OK]

Hint: Always pass array to tags() [OK]

Common Mistakes:

• Passing single string instead of array
• Thinking flush() is disallowed
• Assuming put() needs closure

5. You want to cache user profile data and product data separately but clear both caches together when needed. Which is the best way to use cache tags in Laravel to achieve this?

hard

A. Tag user profiles with ['users'] and products with ['products'], then flush both tags separately

B. Use no tags and clear cache manually by keys

C. Tag both user profiles and products with ['app_data'], then flush this tag to clear all

D. Tag user profiles with ['users'] and products with ['products'], then flush(['users', 'products'])

Solution

1. Step 1: Understand grouping with tags

   To clear multiple cache groups together, use a common tag for both.

2. Step 2: Apply a shared tag

   Tag both user and product caches with a shared tag like 'app_data' to flush all at once.

3. Final Answer:

   Tag both user profiles and products with ['app_data'], then flush this tag to clear all -> Option C

4. Quick Check:

   Shared tag groups caches for joint flush [OK]

Hint: Use shared tag to clear multiple caches together [OK]

Common Mistakes:

• Flushing tags separately instead of shared tag
• Not tagging caches for group clearing
• Trying to flush multiple tags in one call incorrectly