Redirect and render in Ruby on Rails - Mini Project: Build & Apply

Redirect and Render in Rails Controller

📖 Scenario: You are building a simple Rails web app that manages books. You want to practice how to control what the app shows or where it sends the user after certain actions.

🎯 Goal: Learn how to use redirect_to and render in a Rails controller to control page flow and display.

📋 What You'll Learn

Create a controller action with a variable

Add a configuration variable to decide behavior

Use redirect_to or render based on the variable

Complete the controller action with correct Rails syntax

💡 Why This Matters

🌍 Real World

Redirecting and rendering are common in web apps to control what users see after actions like form submissions or page visits.

💼 Career

Understanding redirect_to and render is essential for Rails developers to manage user navigation and display content correctly.

1

Create a controller action with a variable

In the BooksController, create an action called show_message. Inside it, create a variable called message and set it to the string 'Welcome to the Book Store'.

Ruby on Rails

class BooksController < ApplicationController
  # Create show_message action with message variable
  # Your code here
end

Hint

Define a method show_message inside the controller and assign the string to message.

2

Add a configuration variable to decide behavior

Inside the show_message action, add a variable called should_redirect and set it to true.

Ruby on Rails

class BooksController < ApplicationController
  def show_message
    message = 'Welcome to the Book Store'
    # Add should_redirect variable here
    # Your code here
  end
end

Hint

Just add should_redirect = true inside the action.

3

Use redirect_to or render based on the variable

Inside the show_message action, add an if statement that checks should_redirect. If it is true, use redirect_to root_path. Otherwise, use render plain: message.

Ruby on Rails

class BooksController < ApplicationController
  def show_message
    message = 'Welcome to the Book Store'
    should_redirect = true
    # Use if statement to redirect or render
    # Your code here
  end
end

Hint

Use if should_redirect then redirect_to root_path, else render plain: message.

4

Complete the controller action with correct Rails syntax

Ensure the show_message action is properly closed with end keywords for both the if and the method. The full controller should be valid Ruby code.

Ruby on Rails

class BooksController < ApplicationController
  def show_message
    message = 'Welcome to the Book Store'
    should_redirect = true
    if should_redirect
      redirect_to root_path
    else
      render plain: message
    end
  end
end
# Check syntax and completeness

Hint

Make sure all end keywords are present to close the method and the class.

Practice

1. What does redirect_to do in a Rails controller?

easy

A. Stops the server from processing the request

B. Displays a view template without changing the URL

C. Sends the user to a different URL and starts a new request

D. Reloads the current page without any changes

Solution

1. Step 1: Understand the purpose of redirect_to

   redirect_to tells the browser to go to a new URL, causing a new HTTP request.

2. Step 2: Compare with render

   render shows a view without changing the URL or making a new request, unlike redirect_to.

3. Final Answer:

   Sends the user to a different URL and starts a new request -> Option C

4. Quick Check:

   redirect_to = new request and URL change [OK]

Hint: Redirect changes URL and request; render does not [OK]

Common Mistakes:

• Confusing render with redirect_to
• Thinking redirect_to does not change URL
• Assuming redirect_to renders a view template

2. Which of the following is the correct syntax to render the edit template in a Rails controller?

easy

A. redirect_to :edit

B. render :edit

C. render_to :edit

D. redirect :edit

Solution

1. Step 1: Recall the syntax for rendering templates

   In Rails, to show a view template without redirecting, use render :template_name.

2. Step 2: Identify the correct option

   Only render :edit is valid syntax to render the edit view.

3. Final Answer:

   render :edit -> Option B

4. Quick Check:

   render :template_name syntax = render :edit [OK]

Hint: Use render with colon and template name to show views [OK]

Common Mistakes:

• Using redirect_to instead of render to show a view
• Using incorrect method names like render_to
• Missing colon before template name

3. Given this Rails controller code:

def create
  @post = Post.new(post_params)
  if @post.save
    redirect_to @post
  else
    render :new
  end
end

What happens when @post.save returns false?

medium

A. The browser reloads the current page without changes

B. The user is redirected to the post's show page

C. The server raises an exception

D. The new post form is shown again with errors

Solution

1. Step 1: Analyze the if-else condition

   If @post.save is true, it redirects to the post's show page. If false, it renders the new template.

2. Step 2: Understand render behavior on failure

   Rendering :new shows the form again, usually with error messages, without changing the URL.

3. Final Answer:

   The new post form is shown again with errors -> Option D

4. Quick Check:

   save false triggers render :new = The new post form is shown again with errors [OK]

Hint: If save fails, render form again; if success, redirect [OK]

Common Mistakes:

• Thinking redirect happens on save failure
• Assuming an error is raised automatically
• Confusing render with redirect behavior

4. Identify the error in this Rails controller code:

def update
  @user = User.find(params[:id])
  if @user.update(user_params)
    render redirect_to @user
  else
    render :edit
  end
end

medium

A. Using render redirect_to @user is invalid syntax

B. Missing end for the method

C. Should use redirect_to :edit instead of render :edit

D. No error, code works fine

Solution

1. Step 1: Check the line with render redirect_to @user

   This line tries to combine render and redirect_to, which is invalid syntax in Rails.

2. Step 2: Correct usage of redirect and render

   Use either redirect_to @user alone to redirect, or render :template to render a view. They cannot be combined.

3. Final Answer:

   Using render redirect_to @user is invalid syntax -> Option A

4. Quick Check:

   render and redirect_to cannot be combined [OK]

Hint: Use either render or redirect_to, never both together [OK]

Common Mistakes:

• Combining render and redirect_to in one line
• Confusing render :edit with redirect_to :edit
• Forgetting to end method blocks

5. You want to show a form with errors after a failed update, but keep the URL unchanged. Which is the best approach in Rails?

hard

A. Use render :edit to show the form with errors on the same URL

B. Use redirect_to @user to show the user's profile page

C. Use redirect_to edit_user_path(@user) to reload the form

D. Use render redirect_to :edit to combine both

Solution

1. Step 1: Understand URL behavior for forms with errors

   To keep the URL unchanged and show errors, you must render the form template again without redirecting.

2. Step 2: Choose the correct method

   render :edit displays the edit form with errors on the same URL, while redirect_to changes the URL and starts a new request, losing error info.

3. Final Answer:

   Use render :edit to show the form with errors on the same URL -> Option A

4. Quick Check:

   Render keeps URL, redirect changes it [OK]

Hint: Render to keep URL and show errors; redirect loses error data [OK]

Common Mistakes:

• Using redirect_to which loses error messages
• Trying to combine render and redirect_to
• Assuming redirect_to reloads form with errors