First Rails application - Mini Project: Build & Apply

First Rails application

📖 Scenario: You want to create a simple web app that shows a welcome message on the homepage. This is your first step into building with Rails, a popular web framework.

🎯 Goal: Build a basic Rails app with a homepage that displays the text "Welcome to My First Rails App!"

📋 What You'll Learn

Create a new Rails application named my_first_app

Generate a controller named home with an index action

Set the root route to the home#index action

Create a view for the index action that displays the welcome message

💡 Why This Matters

🌍 Real World

Creating a basic Rails app is the first step to building websites and web services that can handle user requests and show dynamic content.

💼 Career

Understanding how to set up a Rails app, create controllers, routes, and views is essential for web developer roles that use Ruby on Rails.

1

Create a new Rails application

Run the command rails new my_first_app in your terminal to create a new Rails application named my_first_app.

Ruby on Rails

# Run the command below in your terminal
# rails new my_first_app

Hint

Use the rails new command followed by the app name my_first_app.

2

Generate a controller with an index action

Inside the my_first_app directory, run rails generate controller home index to create a controller named home with an index action.

Ruby on Rails

# Run the command below in your terminal inside my_first_app folder
# rails generate controller home index

Hint

Use rails generate controller home index to create the controller and action.

3

Set the root route to home#index

Open the file config/routes.rb and add the line root 'home#index' to set the homepage route to the index action of the home controller.

Ruby on Rails

Rails.application.routes.draw do
  # Set the root route here
  # Your code here
end

Hint

In config/routes.rb, add root 'home#index' inside the Rails.application.routes.draw do block.

4

Create the view with welcome message

Open the file app/views/home/index.html.erb and add the line <h1>Welcome to My First Rails App!</h1> to display the welcome message on the homepage.

Ruby on Rails

Hint

Edit app/views/home/index.html.erb and add an <h1> tag with the welcome text.

Practice

1. What command do you use to create a new Rails application folder?

easy

A. rails init myapp

B. rails new myapp

C. rails create myapp

D. rails start myapp

Solution

1. Step 1: Understand Rails app creation command

   The official command to create a new Rails app is rails new followed by the app name.

2. Step 2: Match the command with options

   Only rails new myapp uses rails new myapp, which is correct syntax.

3. Final Answer:

   rails new myapp -> Option B

4. Quick Check:

   Create app folder = rails new [OK]

Hint: Remember: 'rails new' creates the app folder [OK]

Common Mistakes:

• Using 'rails start' instead of 'rails new'
• Confusing 'rails create' with 'rails new'
• Trying 'rails init' which is not a Rails command

2. Which command starts the Rails server so you can view your app in a browser?

easy

A. rails launch

B. rails start

C. rails run

D. rails server

Solution

1. Step 1: Identify the command to run the Rails server

   The correct command to start the Rails server is rails server.

2. Step 2: Compare with options

   Only rails server matches the correct command exactly.

3. Final Answer:

   rails server -> Option D

4. Quick Check:

   Start server = rails server [OK]

Hint: Use 'rails server' to launch your app locally [OK]

Common Mistakes:

• Typing 'rails start' which is invalid
• Using 'rails run' which does not start the server
• Trying 'rails launch' which is not a Rails command

3. What will happen if you run rails new blog and then cd blog followed by rails server?

medium

A. A new Rails app named 'blog' is created and the server starts to serve it locally.

B. An error occurs because 'rails server' must be run before 'rails new'.

C. The server starts but shows a blank page because no views are created yet.

D. The command fails because 'cd blog' is not a valid Rails command.

Solution

1. Step 1: Understand the sequence of commands

   rails new blog creates a new app folder named 'blog'. cd blog moves into that folder. rails server starts the server for that app.

2. Step 2: Analyze the expected behavior

   Running these commands in order creates the app and starts the server correctly, serving the default Rails welcome page.

3. Final Answer:

   A new Rails app named 'blog' is created and the server starts to serve it locally. -> Option A

4. Quick Check:

   rails new + cd + rails server = app runs [OK]

Hint: Create app, enter folder, then start server to see app [OK]

Common Mistakes:

• Thinking 'rails server' must run before app creation
• Assuming 'cd blog' is a Rails command instead of shell
• Expecting an error when running these commands in order

4. You ran rails new myapp but when you try rails server inside the folder, you get an error. What is the most likely cause?

medium

A. You must create a controller before starting the server.

B. You need to run rails start instead of rails server.

C. You forgot to run bundle install to install dependencies.

D. The folder name 'myapp' is invalid for Rails apps.

Solution

1. Step 1: Identify common setup step after creating app

   After rails new, you usually run bundle install to install gems needed by the app.

2. Step 2: Understand error cause

   If dependencies are missing, rails server will fail to start due to missing gems.

3. Final Answer:

   You forgot to run bundle install to install dependencies. -> Option C

4. Quick Check:

   Missing gems? Run bundle install first [OK]

Hint: Run 'bundle install' after 'rails new' before starting server [OK]

Common Mistakes:

• Trying 'rails start' which is invalid
• Thinking a controller is required before server start
• Believing folder name causes the error

5. You want to create a new Rails app named shop and immediately start the server. Which sequence of commands is correct?

hard

A. rails new shop -> cd shop -> rails server

B. rails create shop -> rails server

C. rails new shop -> rails server

D. cd shop -> rails new shop -> rails server

Solution

1. Step 1: Create the app folder with correct command

   Use rails new shop to create the app folder named 'shop'.

2. Step 2: Change directory into the new app folder

   Run cd shop to move into the app folder before starting the server.

3. Step 3: Start the Rails server inside the app folder

   Run rails server to launch the app locally.

4. Final Answer:

   rails new shop -> cd shop -> rails server -> Option A

5. Quick Check:

   Create app, enter folder, start server = correct order [OK]

Hint: Create app, cd into it, then run server [OK]

Common Mistakes:

• Skipping 'cd' before running server
• Using 'rails create' which is invalid
• Running server outside app folder