How to Use before_action in Rails Controllers

In Rails, before_action is a controller callback that runs specified methods before certain controller actions. You use it by declaring before_action :method_name inside your controller to execute code like authentication or setup before actions run.

Syntax

The before_action method is used inside a Rails controller to specify methods that should run before controller actions. You can limit which actions it applies to using only or except options.

• before_action :method_name - runs method_name before every action.
• before_action :method_name, only: [:action1, :action2] - runs only before listed actions.
• before_action :method_name, except: [:action3] - runs before all except listed actions.

ruby

class ArticlesController < ApplicationController
  before_action :set_article, only: [:show, :edit, :update, :destroy]

  def show
    # action code
  end

  private

  def set_article
    @article = Article.find(params[:id])
  end
end

Example

This example shows a before_action that loads an article before the show and edit actions. It helps avoid repeating the same code in each action.

ruby

class ArticlesController < ApplicationController
  before_action :find_article, only: [:show, :edit]

  def show
    render plain: "Showing article: #{@article.title}"
  end

  def edit
    render plain: "Editing article: #{@article.title}"
  end

  private

  def find_article
    @article = Article.find(params[:id])
  end
end

Output

Showing article: Example Title (when accessing show with id param)

Common Pitfalls

Common mistakes when using before_action include:

• Forgetting to make the callback method private, exposing it as an action.
• Not specifying only or except when needed, causing callbacks to run unnecessarily.
• Using before_filter which is deprecated in Rails 5 and later.

ruby

class UsersController < ApplicationController
  # Wrong: method is public and can be called as action
  before_action :authenticate_user

  def authenticate_user
    # authentication code
  end
end

# Correct way:
class UsersController < ApplicationController
  before_action :authenticate_user

  private

  def authenticate_user
    # authentication code
  end
end

Quick Reference

Use before_action to run methods before controller actions for setup or checks. Limit callbacks with only or except. Always keep callback methods private to avoid exposing them as actions.

Option	Description
before_action :method_name	Runs method before all actions
before_action :method_name, only: [:a, :b]	Runs method only before listed actions
before_action :method_name, except: [:c]	Runs method before all except listed actions
Make callback methods private	Prevents them from being accessible as actions

Key Takeaways

Use before_action to run methods before controller actions for cleaner code.

Limit callbacks with only or except to avoid unnecessary runs.

Keep callback methods private to prevent them from being called as actions.

Avoid deprecated before_filter; use before_action instead.

before_action helps keep controllers DRY by sharing common setup code.