**Course Title:** Ruby Programming: From Basics to Advanced Techniques **Section Title:** Introduction to Ruby on Rails **Topic:** MVC architecture: models, views, controllers **Welcome to the world of Ruby on Rails** ============================================= In the previous topic, we introduced Ruby on Rails as a powerful web development framework. Now, it's time to dive deeper into the architecture that makes Rails so efficient and scalable: the Model-View-Controller (MVC) pattern. **What is MVC?** ---------------- MVC is a software architectural pattern that separates an application into three interconnected components: * **Model**: represents the data and business logic of the application * **View**: handles the presentation layer, rendering the user interface * **Controller**: acts as the intermediary between the model and view, receiving input and updating the model accordingly **MVC in Ruby on Rails** ------------------------- In Rails, the MVC pattern is implemented as follows: ### Model * **Definition**: A model represents a table in the database, containing data and business logic related to that table. * **Responsibilities**: + Defines the structure of the data + Validates data before it's saved to the database + Provides methods for manipulating data * **Example**: ```ruby # app/models/user.rb class User < ApplicationRecord validates :name, presence: true validates :email, uniqueness: true end ``` In this example, the `User` model has two validations: one for the presence of a `name` attribute and another for the uniqueness of an `email` attribute. ### View * **Definition**: A view is responsible for rendering the user interface of the application. * **Responsibilities**: + Renders templates (e.g., `.html.erb`) to display data to the user + Can access data from the model through the controller * **Example**: ```html <!-- app/views/users/index.html.erb --> <h1/Users</h1> <ul> <% @users.each do |user| %> <li><%= user.name %></li> <% end %> </ul> ``` In this example, the `index.html.erb` template displays a list of users by iterating over the `@users` array, which is made available by the controller. ### Controller * **Definition**: A controller acts as an intermediary between the model and view, receiving input and updating the model accordingly. * **Responsibilities**: + Handles incoming requests (e.g., GET, POST, PUT, DELETE) + Updates the model based on user input + Renders the appropriate view to display data to the user * **Example**: ```ruby # app/controllers/users_controller.rb class UsersController < ApplicationController def index @users = User.all end end ``` In this example, the `UsersController` has an `index` action that retrieves all users from the database and assigns them to the `@users` instance variable, which is then accessed by the view. **MVC Workflow** ---------------- Here's a step-by-step illustration of how the MVC pattern works in Rails: 1. **Request**: The user sends a request to the application (e.g., navigating to `/users`). 2. **Router**: The request is received by the Rails router, which maps the URL to a specific controller action (e.g., `UsersController#index`). 3. **Controller**: The controller action is executed, which updates the model and retrieves data as needed. 4. **Model**: The model performs any necessary data manipulation and validation. 5. **View**: The controller renders the corresponding view, passing any necessary data to the view. 6. **Response**: The view is rendered as the response to the user's request. **Key Takeaways** ---------------- * The MVC pattern separates an application into three interconnected components: model, view, and controller. * The model represents data and business logic, the view handles presentation, and the controller acts as an intermediary between the two. * In Rails, the MVC pattern is implemented using models, views, and controllers. **What's Next?** ---------------- In the next topic, we'll cover setting up a Rails development environment. **Practice Time!** ------------------ Try creating a simple Rails application using the MVC pattern. Create a model for a `Book` entity, with attributes for `title` and `author`. Create a controller to handle CRUD (Create, Read, Update, Delete) operations on the `Book` model. Render a view to display a list of all books. **Need Help?** -------------- Leave a comment below if you have any questions or need help with the exercise. **External Resources** -------------------- * [Rails Documentation: MVC](https://guides.rubyonrails.org/v6.0/getting_started.html#getting-familiar-with-mvc) * [Rails Guides: Active Record Basics](https://guides.rubyonrails.org/v6.0/active_record_basics.html) * [Rails Guides: Action View Overview](https://guides.rubyonrails.org/v6.0/action_view_overview.html)