How to Use Cookies in Rails: Syntax and Examples

In Rails, you use the cookies hash to set, read, and delete cookies. To set a cookie, assign a value like cookies[:user_name] = "value". To read it, use cookies[:user_name], and to delete, use cookies.delete(:user_name).

Syntax

Rails provides a cookies hash to manage cookies easily. You can set a cookie by assigning a value to a key, read it by accessing the key, and delete it using the delete method.

• Set cookie: cookies[:key] = "value"
• Read cookie: cookies[:key]
• Delete cookie: cookies.delete(:key)

You can also set options like expires to control cookie lifetime.

ruby

cookies[:user_name] = "Alice"
user = cookies[:user_name]
cookies.delete(:user_name)
cookies[:user_id] = { value: "123", expires: 1.hour.from_now }

Example

This example shows how to set a cookie with an expiration, read it, and delete it in a Rails controller.

ruby

class UsersController < ApplicationController
  def set_cookie
    cookies[:user_name] = { value: "Alice", expires: 1.hour.from_now }
    render plain: "Cookie set"
  end

  def show_cookie
    user = cookies[:user_name] || "No cookie found"
    render plain: "User cookie: #{user}"
  end

  def delete_cookie
    cookies.delete(:user_name)
    render plain: "Cookie deleted"
  end
end

Output

When visiting /set_cookie: Cookie set
When visiting /show_cookie: User cookie: Alice
After /delete_cookie and then /show_cookie: User cookie: No cookie found

Common Pitfalls

Common mistakes when using cookies in Rails include:

• Not setting an expiration, causing session cookies that disappear when the browser closes.
• Trying to store large or sensitive data in cookies (cookies should be small and not contain secrets).
• Forgetting to delete cookies properly, leading to stale data.
• Not considering cookie security options like secure and httponly.

Always use cookies for small, non-sensitive data and consider using sessions or encrypted cookies for sensitive information.

ruby

## Wrong way (no expiration, storing large data):
cookies[:data] = "a" * 5000

## Right way (small data with expiration):
cookies[:user_id] = { value: "123", expires: 1.hour.from_now, secure: true, httponly: true }

Quick Reference

Action	Syntax	Description
Set cookie	cookies[:key] = "value"	Stores a cookie with default session expiration
Set cookie with options	cookies[:key] = { value: "value", expires: 1.hour.from_now }	Stores cookie with expiration time
Read cookie	cookies[:key]	Retrieves the cookie value or nil if not set
Delete cookie	cookies.delete(:key)	Removes the cookie from the browser

Key Takeaways

Use the cookies hash to set, read, and delete cookies in Rails controllers.

Set cookie expiration to control how long cookies last; otherwise, they expire when the browser closes.

Avoid storing large or sensitive data directly in cookies; use sessions or encrypted cookies instead.

Use security options like secure and httponly to protect cookies.

Always delete cookies properly to avoid stale data.