Before action (`before_action`) trong Rails dùng để làm gì?

before_action là callback chạy trước một hoặc nhiều action của controller — dùng để factoring logic dùng chung (authentication, authorization, load record).

class PostsController < ApplicationController
  before_action :authenticate_user!
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  def show
    # @post đã sẵn sàng từ set_post
  end

  private

  def set_post
    @post = Post.find(params[:id])
  end
end

Nếu before_action gọi render hoặc redirect_to, chuỗi callback dừng và action gốc không chạy.

Các loại khác: after_action, around_action.

before_action is a callback that runs before one or more controller actions — used to factor out shared logic (authentication, authorization, record loading).

class PostsController < ApplicationController
  before_action :authenticate_user!
  before_action :set_post, only: [:show, :edit, :update, :destroy]

  def show
    # @post is already available from set_post
  end

  private

  def set_post
    @post = Post.find(params[:id])
  end
end

If a before_action calls render or redirect_to, the callback chain halts and the original action does not run.

Other types: after_action, around_action.