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Caching with Instance Variables in Ruby on Rails

by | Mar 2, 2023 | Caching | 0 comments

Caching is an important aspect of web development that helps to improve the performance and speed of web applications. In Ruby on Rails, caching is implemented using different techniques such as page caching, action caching, and fragment caching. In this blog post, we will explore the use of instance variables for caching in Ruby on Rails.

What are Instance Variables?

In Ruby, instance variables are variables that are scoped to an instance of a class. They are prefixed with the “@” symbol and can be accessed within the instance’s methods. For example, consider the following code snippet:

class Person
  def initialize(name)
    @name = name

  def greet
    "Hello, #{@name}!"

person ="John")
puts person.greet

In this code snippet, the @name instance variable is initialized with the name parameter passed to the constructor. The greet method uses the @name instance variable to construct a greeting message.

Using Instance Variables for Caching

In Ruby on Rails, instance variables can be used for caching data that is frequently accessed within an action or across multiple actions. This can be achieved by assigning the cached data to an instance variable within an action and then using that instance variable in subsequent requests.

Consider the following code snippet:

class ProductsController < ApplicationController
  def index
    @products = Rails.cache.fetch('all_products', expires_in: 5.minutes) do

In this code snippet, the index action retrieves all products from the database and assigns them to the @products instance variable. However, instead of querying the database on every request, the data is cached using the Rails.cache.fetch method. The expires_in option specifies the amount of time before the cached data expires and needs to be refreshed.

When a user visits the index page for the first time, the cached data is not yet available and the block passed to Rails.cache.fetch is executed to retrieve the data from the database. Subsequent requests to the index action will use the cached data stored in the @products instance variable, thereby improving the performance of the application.


In this blog post, we have explored the use of instance variables for caching data in Ruby on Rails. Using instance variables for caching can help to improve the performance and speed of web applications by reducing the number of database queries and computations required. However, it is important to ensure that cached data is refreshed at regular intervals to avoid stale data being served to users.

Kirk Makse

Author: Kirk Makse

Greetings, my name is Kirk. I’m the creator of Rails Zone and a passionate Ruby on Rails developer. During my free time, I develop helpful tools and tutorials that aid fellow Ruby on Rails developers in creating applications with improved efficiency and speed.