Using Filters and Callbacks for Controller Logic

1. Introduction

1.1 Tutorial's Goal

This tutorial guides you through the process of using filters and callbacks in Rails. Rails filters and callbacks are powerful tools that allow you to run specific code at specific times during the controller's lifecycle.

1.2 Learning Outcomes

By the end of this tutorial, you will be able to:
- Understand what filters and callbacks are in Rails.
- Use filters and callbacks in your Rails applications.
- Implement controller logic efficiently using filters and callbacks.

1.3 Prerequisites

Basic understanding of Ruby on Rails and MVC architecture is required.

2. Step-by-Step Guide

2.1 Filters

Filters are methods that are run "before", "after" or "around" a controller action. They are inherited, so if you set a filter on ApplicationController, it will be run on every controller in your application.

class ApplicationController < ActionController::Base
  before_action :authenticate

  def authenticate
    # authentication logic here
  end
end

In the above code, :authenticate method will be executed before every action in your application.

2.2 Callbacks

Callbacks are methods that get called at certain moments of an object's life cycle. For example, you might want to run a custom method before an object is saved. Callbacks make this possible.

class Post < ApplicationRecord
  before_save :capitalize_title

  def capitalize_title
    self.title.capitalize!
  end
end

In this example, the capitalize_title method will be run before every save of a Post object.

3. Code Examples

3.1 Before Action Filter

class PostsController < ApplicationController
  before_action :find_post, only: [:show, :edit, :update, :destroy]

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

In this code, find_post method is executed before the actions 'show', 'edit', 'update' and 'destroy'. This reduces redundancy as we do not have to write the same line of code for these actions.

3.2 After Callback

class User < ApplicationRecord
  after_create :send_welcome_email

  def send_welcome_email
    UserMailer.welcome(self).deliver
  end
end

In this example, send_welcome_email is a callback that is executed after a User object is created. This is useful for sending a welcome email to a new user after they register.

4. Summary

In this tutorial, we discussed filters and callbacks in Rails. We learned how to use before_action and after_create to run code at specific times. We also saw how these tools can help us write DRY (Don't Repeat Yourself) and clean code.

For further learning, you can explore other types of filters and callbacks in Rails, such as around_action and before_save.

5. Practice Exercises

5.1 Exercise 1

Create a before_action filter to authenticate a user before every action in the OrdersController.

5.2 Exercise 2

Create an after_save callback in the Comment model to send a notification email to the post author whenever a new comment is saved.

5.3 Exercise 3

Create an around_save callback in the Product model to measure how long the save operation takes.

Hint: You can use Time.now before and after the yield to get the start time and end time.

Take time to practice these concepts to get a better understanding. Happy coding!