Low-level caching with Rails.cache - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Rails.cache used for in Rails applications?

Rails.cache is used to store data temporarily to speed up repeated access. It helps avoid doing the same work multiple times by saving results and reusing them.

beginner

How do you write data to the cache using Rails.cache?

You use Rails.cache.write(key, value, options). The key identifies the cached data, and value is what you want to store.

beginner

What method do you use to read data from the cache with Rails.cache?

You use Rails.cache.read(key). It returns the cached value if it exists or nil if not.

intermediate

Explain the purpose of Rails.cache.fetch.

Rails.cache.fetch(key) { block } tries to read the cached value for key. If it’s missing, it runs the block, stores the result in the cache, and returns it. This combines reading and writing in one step.

intermediate

Why is setting an expiration time important when caching with Rails.cache?

Expiration time ensures cached data doesn’t stay forever. It helps keep data fresh and prevents using outdated information.

Which method reads a value from the cache in Rails?

A Rails.cache.clear()

B Rails.cache.write(key, value)

C Rails.cache.delete(key)

D Rails.cache.read(key)

Rails.cache.read(key) reads the cached value for the given key.

What does Rails.cache.fetch do if the key is not found in the cache?

A Runs the block, stores its result, and returns it

B Returns nil

C Raises an error

D Deletes the cache

fetch runs the block, caches the result, and returns it if the key is missing.

How do you set an expiration time when writing to the cache?

A Rails.cache.write(key, value, expires_in: time)

B Rails.cache.write(key, value, timeout: time)

C Rails.cache.write(key, value, expire: time)

D Rails.cache.write(key, value, ttl: time)

The option expires_in sets how long the cache lasts.

Which of these is NOT a benefit of using low-level caching with Rails.cache?

A Speeds up repeated data access

B Reduces database load

C Automatically fixes bugs in code

D Stores expensive computation results

Caching improves speed and reduces load but does not fix bugs.

What happens if you try to read a cache key that does not exist?

A Returns false

B Returns nil

C Raises an exception

D Returns an empty string

Rails.cache.read returns nil if the key is missing.

Describe how you would use Rails.cache.fetch to cache the result of a slow database query.

Think about combining reading and writing cache in one step.

Explain why caching with expiration is important in a web application.

Consider what happens if cache never expires.