10. Query cache

 

Query cache

1. @Cacheable

  Used to read from cache if available, otherwise executes the method and stores the result in cache.

  When to use: For read-heavy operations (e.g., fetching data from DB).

Example:

@Cacheable("users")
public User getUserById(Long id) {
    System.out.println("Fetching from DB...");
    return userRepository.findById(id).orElse(null);
}

 

 What happens:

• First call with `id = 1`: fetches from DB and caches the result.
• Second call with `id = 1`: returns result from cache, no DB hit.

 

 2. @CachePut

Always executes the method and updates the cache with the result.

When to use: When data is updated, and cache should be refreshed.

Example:

@CachePut(value = "users", key = "#user.id")
public User updateUser(User user) {
    return userRepository.save(user); // saves to DB and updates cache
}

 What happens:

• Always hits DB.
• Updates the cache with new value.

 3. @CacheEvict

 Used to remove a cache entry or clear cache.

 When to use: When data is deleted or changed, and cache needs to be cleared.

 Example:

@CacheEvict(value = "users", key = "#id")
public void deleteUser(Long id) {
    userRepository.deleteById(id); // removes from DB and cache
}

What happens:

• Deletes user from DB.
• Removes cache entry with matching `id`.

we can use any name for "users" in @Cacheable("users")

@Cacheable("myUserCache")
public User getUserById(Long id) { ... }

 

But:

This name must match in all related annotations (@CachePut, @CacheEvict, etc.) to work with the same cache.

It’s just an identifier for the cache region.

We should use as "user.id" because #user refers to the method parameter User user.

@CachePut(value = "users", key = "#user.id")
public User updateUser(User user) {
    return userRepository.save(user); // saves to DB and updates cache
}

 

Annotation	DB Hit	Cache Used	Cache Updated	Use Case
@Cacheable	No (if cached)	Yes	No	Fetch and cache result
@CachePut	Yes	No	Yes	Update cache after method
@CacheEvict	Yes	N/A	N/A (clears)	Remove from cache