Action methods in Ruby on Rails - Mini Project: Build & Apply

Building Action Methods in Rails Controller

📖 Scenario: You are creating a simple Rails application to manage a list of books. Each book has a title and an author. You want to build action methods in a controller to show a list of books and display details of a single book.

🎯 Goal: Build a Rails controller with action methods index and show to list all books and show details of one book.

📋 What You'll Learn

Create a BooksController class

Add an index action method that sets @books to all books

Add a show action method that finds a book by params[:id] and sets @book

Use Rails conventions for controller and action methods

💡 Why This Matters

🌍 Real World

Controllers in Rails handle user requests and prepare data for views. Action methods like index and show are common for listing and displaying records.

💼 Career

Understanding how to write action methods in Rails controllers is essential for backend web development roles using Ruby on Rails.

1

Create BooksController class

Create a Rails controller class called BooksController that inherits from ApplicationController.

Ruby on Rails

# Your code here

Hint

Controllers in Rails are classes that inherit from ApplicationController.

2

Add index action method

Inside the BooksController class, add an index action method that sets an instance variable @books to Book.all.

Ruby on Rails

class BooksController 
  # Your code here
end

Hint

Action methods are defined with def and set instance variables for views.

3

Add show action method

Inside the BooksController class, add a show action method that sets an instance variable @book by finding a book with Book.find(params[:id]).

Ruby on Rails

class BooksController < ApplicationController
  def index
    @books = Book.all
  end

  # Your code here
end

Hint

The show action finds a single record using params[:id].

4

Complete controller with both actions

Ensure the BooksController class contains both index and show action methods exactly as specified.

Ruby on Rails

class BooksController < ApplicationController
  def index
    @books = Book.all
  end

  def show
    @book = Book.find(params[:id])
  end
end
# Verify both actions are present

Hint

Double-check both action methods are inside the controller class.

Practice

1. What is the primary role of an action method in a Rails controller?

easy

A. To respond to user requests by processing data and rendering views or redirects

B. To define database schema and migrations

C. To style the HTML pages with CSS

D. To manage server configuration settings

Solution

1. Step 1: Understand the purpose of action methods

   Action methods in Rails controllers handle user requests by processing data and deciding what to show next.

2. Step 2: Differentiate from other roles

   Database schema, styling, and server settings are handled elsewhere, not in action methods.

3. Final Answer:

   To respond to user requests by processing data and rendering views or redirects -> Option A

4. Quick Check:

   Action methods handle requests = A [OK]

Hint: Action methods handle requests and responses in controllers [OK]

Common Mistakes:

• Confusing action methods with database migrations
• Thinking action methods style pages
• Assuming action methods configure servers

2. Which of the following is the correct syntax to define an action method named show in a Rails controller?

easy

A. function show() {}

B. def show; end

C. show() => {}

D. def show() {}

Solution

1. Step 1: Recall Ruby method syntax in Rails controllers

   Rails controller actions are Ruby methods defined with def method_name; end.

2. Step 2: Identify correct syntax

   def show; end uses correct Ruby syntax without parentheses, which is common in Rails.

3. Final Answer:

   def show; end -> Option B

4. Quick Check:

   Ruby method syntax = A [OK]

Hint: Rails actions use Ruby method syntax: def name; end [OK]

Common Mistakes:

• Using JavaScript function syntax
• Adding parentheses with braces in Ruby
• Mixing arrow functions with Ruby

3. Given this Rails controller action:

def index
  @users = User.all
end

What will @users contain after this action runs?

medium

A. A hash of user attributes

B. A single User record

C. An array of all User records from the database

D. An empty array

Solution

1. Step 1: Understand User.all in Rails

   User.all fetches all records from the users table as an ActiveRecord collection (like an array).

2. Step 2: Determine the content of @users

   It will contain all user records, not just one or empty or a hash.

3. Final Answer:

   An array of all User records from the database -> Option C

4. Quick Check:

   User.all returns all records = D [OK]

Hint: User.all fetches all records as a collection [OK]

Common Mistakes:

• Thinking User.all returns a single record
• Assuming it returns a hash
• Confusing with empty array if no users exist

4. Identify the error in this Rails controller action:

def create
  @user = User.new(params[:user])
  if @user.save
    redirect_to @user
  else
    render :new
  end
end

medium

A. Missing an end keyword

B. Using render instead of redirect_to in else

C. Redirecting to @user instead of a URL string

D. Using params[:user] directly without strong parameters

Solution

1. Step 1: Check parameter handling in create action

   Rails requires strong parameters to whitelist allowed attributes for security.

2. Step 2: Identify misuse of params[:user]

   Using params[:user] directly is unsafe and will cause an error in modern Rails.

3. Final Answer:

   Using params[:user] directly without strong parameters -> Option D

4. Quick Check:

   Strong parameters needed = B [OK]

Hint: Always use strong parameters for mass assignment [OK]

Common Mistakes:

• Ignoring strong parameters security
• Thinking redirect_to needs a URL string only
• Missing end keyword (not true here)

5. You want to add a custom action method publish to your PostsController that changes a post's status to 'published' and then redirects to the post's page. Which code snippet correctly implements this?

hard

A. def publish
@post = Post.find(params[:id])
@post.status = 'published'
@post.save
redirect_to post_path(@post)
end

B. def publish
@post = Post.find(params[:id])
@post.status = 'published'
redirect_to post_path(@post)
end

C. def publish
@post = Post.find(params[:id])
@post.status = 'published'
redirect_to @post
end

D. def publish
@post = Post.find(params[:id])
@post.save(status: 'published')
redirect_to @post
end

Solution

1. Step 1: Find the post by ID

   All options correctly find the post using Post.find(params[:id]).

2. Step 2: Update the post's status and save changes

   def publish @post = Post.find(params[:id]) @post.status = 'published' redirect_to @post end changes status but does not save. def publish @post = Post.find(params[:id]) @post.status = 'published' redirect_to post_path(@post) end changes status but does not save. def publish @post = Post.find(params[:id]) @post.status = 'published' @post.save redirect_to post_path(@post) end changes status, calls save, then redirects. def publish @post = Post.find(params[:id]) @post.save(status: 'published') redirect_to @post end incorrectly uses save(status: 'published') which is invalid.

3. Step 3: Redirect to the post's show page

   Options A, C, and D redirect correctly. def publish @post = Post.find(params[:id]) @post.status = 'published' redirect_to post_path(@post) end uses post_path(@post) which is also correct.

4. Final Answer:

   def publish @post = Post.find(params[:id]) @post.status = 'published' @post.save redirect_to post_path(@post) end -> Option A

5. Quick Check:

   Change attribute + save + redirect = C [OK]

Hint: Change attribute, save record, then redirect [OK]

Common Mistakes:

• Forgetting to save after changing attribute
• Using invalid save syntax with parameters
• Not redirecting after update