1. Introduction

This tutorial's goal is to provide a comprehensive understanding of the 'app', 'config', and 'db' directories in a Rails project. These directories are critical components of any Rails application and understanding their structure and usage is key to becoming an efficient Rails developer.

By the end of this tutorial, you'll be able to:

• Understand the purpose of 'app', 'config', and 'db' directories in a Rails project
• Identify the types of files in each directory
• Use these directories correctly in your Rails applications

Prerequisites: This tutorial assumes that you have a basic understanding of Ruby on Rails. If you're new to Rails, I recommend completing a beginner's tutorial first.

2. Step-by-Step Guide

App Directory

The 'app' directory is where you'll spend most of your time. It contains the MVC (Model, View, Controller) components of your Rails application.

• Models: These represent the application's data structure, typically stored in the database.
• Views: These represent the user interface of your application.
• Controllers: These act as an intermediary between models and views.

Config Directory

The 'config' directory stores configuration files that Rails uses to start and run your application. This includes the routes.rb file, which defines the URLs your application responds to, and the database.yml file, which sets up your database.

DB Directory

The 'db' directory contains everything related to the database. This includes schema.rb (a snapshot of your current database structure), and seeds.rb (a file where you can write code to populate your database with initial data).

3. Code Examples

Here are some examples of what you might find in each of these directories.

App Directory: Model

# app/models/user.rb
class User < ApplicationRecord
  # This is a model representing a user in your application.
  # You can add validations, associations, and other logic here.
end

Config Directory: Routes

# config/routes.rb
Rails.application.routes.draw do
  # This file is where you define the URLs your application can respond to.
  # For example, this line creates routes for viewing, creating, editing, and deleting users:
  resources :users
end

DB Directory: Seeds

# db/seeds.rb
User.create(name: "John Doe", email: "johndoe@example.com", password: "password")
# This file lets you populate your database with initial data.
# This line creates a new user with the specified name, email, and password.

4. Summary

In this tutorial, we've covered the 'app', 'config', and 'db' directories in a Rails project. We've learned that:

• The 'app' directory houses the MVC components of your application.
• The 'config' directory contains configuration files for your application.
• The 'db' directory stores everything related to the database.

For further study, I'd recommend looking into how Rails uses the 'lib', 'public', and 'test' directories, among others.

5. Practice Exercises

1. Create a new Rails application and explore the 'app', 'config', and 'db' directories. What files do you find in each?

2. Add a new model to your application. Where do you put the file?

3. Add a new route to your application. Where do you put the code?

Solutions:

1. The specific files you find may vary, but you should see models, views, and controllers in 'app'; configuration files in 'config'; and database-related files in 'db'.

2. Model files go in 'app/models'.

3. Route definitions go in 'config/routes.rb'.