Controller generation in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the default action created by rails generate controller?

You run rails generate controller Products. Which action is created by default in the generated controller?

A A <code>new</code> action is created by default.

B An <code>index</code> action is created by default.

C A <code>show</code> action is created by default.

D No actions are created by default; you must specify them explicitly.

💡 Hint

Think about what happens if you don't specify any actions when generating a controller.

When you run rails generate controller Products without specifying actions, Rails creates the controller file with no actions inside. You must explicitly list actions to generate them.

📝 Syntax

intermediate

Which command generates a controller with index and show actions?

Select the correct Rails command to generate a controller named Articles with index and show actions.

A rails generate controller Articles index show

B rails generate controller Articles --actions=index,show

C rails generate controller Articles -a index show

D rails generate controller Articles --with=index show

💡 Hint

Check the official Rails generator syntax for specifying actions.

The correct syntax is to list the actions after the controller name separated by spaces. Options like --actions or -a are not valid.

❓ state_output

advanced

What files are created by rails generate controller Users new edit?

After running rails generate controller Users new edit, which of the following files is NOT created?

A app/models/user.rb

B app/views/users/new.html.erb

C app/views/users/edit.html.erb

D app/controllers/users_controller.rb

💡 Hint

Consider what the controller generator creates versus the model generator.

The controller generator creates the controller file and view templates for the specified actions. It does not create model files.

🔧 Debug

advanced

Why does rails generate controller Posts show fail with uninitialized constant PostsController error?

You ran rails generate controller Posts show but when visiting /posts/show you get uninitialized constant PostsController. What is the most likely cause?

A The <code>show</code> action is missing inside <code>PostsController</code>.

B The route for <code>/posts/show</code> is missing in <code>config/routes.rb</code>.

C The controller file was not saved or generated properly.

D The model <code>Post</code> is not defined.

💡 Hint

The error means Rails cannot find the controller class at all.

uninitialized constant PostsController means Rails cannot find the controller class. This usually happens if the controller file was not created or saved correctly.

🧠 Conceptual

expert

What is the effect of adding --skip-routes when generating a controller?

You run rails generate controller Comments index --skip-routes. What is the effect of the --skip-routes option?

A It skips generating the controller file but creates views and routes.

B It prevents Rails from adding a route for the <code>index</code> action automatically.

C It disables generating view templates for the controller actions.

D It skips creating the controller test files.

💡 Hint

Think about what Rails normally does with routes when generating a controller.

By default, Rails adds a route for each generated action. The --skip-routes option prevents this automatic route creation.

Practice

1. What does the rails generate controller command do in a Rails application?

easy

A. Compiles the Rails application for production.

B. Generates a new database table for storing data.

C. Deletes an existing controller and its views.

D. Creates a new controller file with specified actions and related view files.

Solution

1. Step 1: Understand the purpose of the command

   The rails generate controller command is used to create a new controller in a Rails app.

2. Step 2: Identify what files are created

   This command creates a controller file and also generates view files for the actions specified.

3. Final Answer:

   Creates a new controller file with specified actions and related view files. -> Option D

4. Quick Check:

   Controller generation = creates controller and views [OK]

Hint: Controller generator creates controller and views together [OK]

Common Mistakes:

• Confusing controller generation with database migration
• Thinking it compiles or deletes files
• Assuming it only creates views without controller

2. Which of the following is the correct syntax to generate a controller named Products with actions index and show?

easy

A. rails generate controller Products index show

B. rails create controller Products index show

C. rails generate model Products index show

D. rails generate controller products index show

Solution

1. Step 1: Identify the correct command keyword

   The correct command to generate a controller is rails generate controller.

2. Step 2: Check the controller name and actions

   Controller names are capitalized (e.g., Products) and actions follow after the name.

3. Final Answer:

   rails generate controller Products index show -> Option A

4. Quick Check:

   Correct syntax = rails generate controller + ControllerName + actions [OK]

Hint: Use 'rails generate controller' with capitalized controller name [OK]

Common Mistakes:

• Using 'create' instead of 'generate'
• Using 'model' instead of 'controller'
• Using lowercase controller name

3. Given the command rails generate controller Articles new edit, which files will be created?

medium

A. Only the controller file articles_controller.rb without views.

B. Model file article.rb and migration for articles table.

C. Controller file articles_controller.rb and views new.html.erb and edit.html.erb.

D. Database schema file and routes for articles.

Solution

1. Step 1: Understand what the generate controller command creates

   It creates a controller file named after the pluralized controller name and view files for each action.

2. Step 2: Identify the files created for actions

   Actions new and edit generate corresponding view files new.html.erb and edit.html.erb.

3. Final Answer:

   Controller file articles_controller.rb and views new.html.erb and edit.html.erb. -> Option C

4. Quick Check:

   Controller + views for actions = Controller file articles_controller.rb and views new.html.erb and edit.html.erb. [OK]

Hint: Controller generator creates views for each action named [OK]

Common Mistakes:

• Confusing controller generation with model generation
• Expecting database files to be created
• Thinking views are not created automatically

4. You run rails generate controller users show but get an error. Which of the following is the most likely cause?

medium

A. Controller name should be capitalized as Users.

B. The action show is not allowed in controllers.

C. You must create a model before generating a controller.

D. The command should be rails create controller users show.

Solution

1. Step 1: Check the controller name capitalization

   Rails expects controller names to be capitalized (e.g., Users), lowercase causes errors.

2. Step 2: Verify command correctness

   The command rails generate controller Users show is correct; show is a valid action.

3. Final Answer:

   Controller name should be capitalized as Users. -> Option A

4. Quick Check:

   Capitalized controller name required [OK]

Hint: Always capitalize controller names in generate command [OK]

Common Mistakes:

• Using lowercase controller names
• Thinking actions are restricted
• Confusing generate with create command

5. You want to generate a controller named Admin::Dashboard with actions index and stats. Which command correctly creates the controller and places it in the admin folder?

hard

A. rails generate controller admin/dashboard index stats

B. rails generate controller Admin::Dashboard index stats

C. rails generate controller Admin_Dashboard index stats

D. rails generate controller admin_dashboard index stats

Solution

1. Step 1: Understand namespacing in Rails controllers

   Using :: in the controller name creates a folder structure for namespacing (e.g., Admin::Dashboard creates admin/dashboard_controller.rb).

2. Step 2: Identify the correct command syntax

   The correct syntax uses capitalized names with :: to separate namespace and controller name.

3. Final Answer:

   rails generate controller Admin::Dashboard index stats -> Option B

4. Quick Check:

   Namespace with :: and capitalized names [OK]

Hint: Use :: for namespaced controllers with capitalized parts [OK]

Common Mistakes:

• Using underscores instead of :: for namespaces
• Using lowercase names for namespaces
• Confusing folder path with command syntax