Sinatra Mvc File Structure


We'll review the file structure we'll be using for our MVC Sinatra applications.


  1. Explain the files and folders in a Sinatra MVC file structure
  2. Describe the different folders in the app directory and create new files and add code to these folders
  3. Complete and run a Sinatra MVC application

Keeping Code Organized

We could, if we wanted to, write our entire app in a single file. As you might imagine, this would make things very difficult to read and debug.

Keeping our code organized is crucial when developing complex applications. This concept is called separation of concerns and single responsibility. Each file in our application will have a different responsibility and we'll keep these responsibilities split up into reasonable chunks.

You'll be coding along in this lesson so fork and clone this lab. There are tests to run to make sure your solutions are working. Find the instructions underneath the descriptions for each file you'll be editing.

What does a Sinatra MVC File Structure Look Like?

Take a look at the file structure in this directory. It's okay if it feels overwhelming at first. We're going to walk through the different files and folders and discuss what their responsibilities are.

├── Gemfile
├── app
│   ├── controllers
│   │   └── application_controller.rb
│   ├── models
│   │   └── model.rb
│   └── views
│       └── index.erb
├── config
│   └── environment.rb
├── public
│   └── stylesheets
└── spec
    ├── controllers
    ├── features
    ├── models
    └── spec_helper.rb


This holds a list of all the gems needed to run the application. The bundler gem provides us access to a terminal command: bundle install. Bundler will look in the Gemfile and install any gems, as well as any gem dependencies for this application.

Go ahead and enter this command in terminal. It will create a Gemfile.lock file for you, which is just a documentation of the specific gems version that should be installed.

app directory

This folder holds our MVC directories - models, views, and controllers. We spend most of our time coding in this directory.

models directory

This directory holds the logic behind our application. Typically, these files represent either a component of your application, such as a User, Post, or Comment, or a unit of work. Each file in models typically contains a different class. For example, dog.rb would contain a class called Dog. As you might have guessed, models represent the "M" components of the MVC paradigm.

Models represent the data and object logic of our application.

Create a new file in the models directory to create a dog class. This class should have name, breed, and age attributes which can be set on initialization. You should be able to read and write to these attributes. This class should also keep track of each instance of dog created, as well as a class method all to return an array of those instances.

controllers directory

The controllers, such as application_controller.rb, are where the application configurations, routes, and controller actions are implemented. There is typically a class, which in this case we will call ApplicationController, that represents an instance of your application when the server is up and running. The application_controller.rb file represents the "C" components of the MVC paradigm.

(In some simple applications –– including several labs and code-alongs in this track –– the Application Controller will simply be called app.rb and will live in the root directory of the project.)

Sometimes our other controllers will use ApplicationController as an inheritance point so that they inherit all the defaults and behaviors defined in our main ApplicationController. Other times our other controllers will simply inherit from Sinatra::Base.

Controllers represent the application logic, generally; the interface and flow of our application.

Let's go ahead and fill in our controller. You'll notice in application_controller.rb, we have an ApplicationController class that inherits from Sinatra::Base. When we start up a server, the server will spin up an instance of the ApplicationController class to run our app.

You'll also notice there is a configure block already in the controller. This configure block tells the controller where to look to find the views (your pages with HTML to display text in the browser) and the public directory.

When a client makes a request to a server to load an application, the request is received and processed by the controller. We need to set up a controller action to accept the request and respond with the appropriate HTML.

We've created a controller action that can receive and respond to a GET request to the root URL '/'. This GET request loads the index.erb file.

views directory

This directory holds the code that will be displayed in the browser. In a Sinatra app we use .erb files instead of .html files because .erb files allow us to include regular, old HTML tags AND special erb tags which contain Ruby code. We can name them anything we like, but by convention, our file names will match up with the action that renders them. For example, a GET request to / typically renders a file called index.erb.

Views represent how things look and are displayed in our application. We've created a file index.erb that contains some basic HTML code.

We've already told the controller how to load this file in the view. file

A file is necessary when building Rack-based applications and using rackup/shotgun to start the application server (the ru stands for rackup). is first responsible for loading our application environment, code, and libraries.

Once all our code is loaded, then specifies which controllers to load as part of our application using run or use.

In this case, our file contains the line run ApplicationController, which creates an instance of our ApplicationController class that can respond to requests from a client.

config directory

This directory holds an environment.rb file. We'll be using this file to connect up all the files in our application to the appropriate gems and to each other.

This environment.rb file loads Bundler and thus all the gems in our Gemfile, as well as the app directory.

public directory

The public directory holds our front-end assets. In the example above, it holds a css directory with a stylesheet. Javascript directories and any other front-end assets (like image files) should also be stored in public.

spec directory

The spec directory contains any tests for our applications. These tests set up any expectations for the rest of the project. These are often broken down into unit tests for models, controller tests for routes, and feature tests, which check the actual behavior for users.

Don't forget to run your tests!

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