How to Use Redis for Caching in Ruby on Rails

To use Redis for caching in Ruby on Rails, configure Rails to use redis_cache_store by setting config.cache_store = :redis_cache_store with your Redis server URL in config/environments/production.rb. Then use Rails caching methods like Rails.cache.fetch to store and retrieve cached data efficiently.

Syntax

To enable Redis caching in Rails, set the cache store in your environment configuration file. The key parts are:

• config.cache_store: tells Rails which cache backend to use.
• :redis_cache_store: the Redis adapter for caching.
• url: the Redis server address.

Example syntax:

ruby

config.cache_store = :redis_cache_store, { url: 'redis://localhost:6379/1' }

Example

This example shows how to configure Redis caching in config/environments/production.rb and how to cache a value in a controller using Rails.cache.fetch. The cached value is stored in Redis and reused until it expires.

ruby

Rails.application.configure do
  # Use Redis as cache store
  config.cache_store = :redis_cache_store, { url: ENV.fetch('REDIS_URL') { 'redis://localhost:6379/1' } }
end

class ProductsController < ApplicationController
  def index
    @products = Rails.cache.fetch('products_all', expires_in: 12.hours) do
      Product.all.to_a
    end
    render json: @products
  end
end

Output

[{"id":1,"name":"Product A"},{"id":2,"name":"Product B"}, ...]

Common Pitfalls

Common mistakes when using Redis caching in Rails include:

• Not setting the Redis URL correctly, causing connection errors.
• Forgetting to set expires_in, which can lead to stale cache data.
• Using Redis for caching without running a Redis server.
• Not enabling caching in development environment, so cache calls seem ineffective.

Example of a wrong and right cache fetch usage:

ruby

# Wrong: No expiration, cache might never refresh
Rails.cache.fetch('key') { expensive_operation }

# Right: Set expiration to refresh cache periodically
Rails.cache.fetch('key', expires_in: 1.hour) { expensive_operation }

Quick Reference

Concept	Usage	Notes
Set cache store	config.cache_store = :redis_cache_store, { url: 'redis://localhost:6379/1' }	Configure Redis URL and DB index
Cache fetch	Rails.cache.fetch('key', expires_in: 1.hour) { block }	Caches block result with expiration
Clear cache	Rails.cache.delete('key')	Removes cached data by key
Check cache	Rails.cache.exist?('key')	Returns true if key exists in cache

Key Takeaways

Configure Redis as the cache store in Rails environment files using :redis_cache_store.

Use Rails.cache.fetch with an expiration time to store and retrieve cached data safely.

Ensure Redis server is running and accessible at the configured URL.

Set cache expiration to avoid stale data and memory bloat.

Enable caching in the environment to see Redis caching effects.