Redirect and render in Ruby on Rails - Step-by-Step Execution

Concept Flow - Redirect and render

Controller action starts

↓

Decision: Redirect or Render?

Redirect→Send HTTP redirect response

↓

Browser requests new URL

↓

Render view template

↓

New controller action runs

↓

Send HTTP response with HTML

↓

Request ends

The controller decides to either redirect the browser to a new URL or render a view template directly, sending the appropriate HTTP response.

Execution Sample

Ruby on Rails

def show
  if user_signed_in?
    redirect_to dashboard_path
  else
    render :login
  end
end

This controller action redirects signed-in users to the dashboard, otherwise renders the login page.

Execution Table

Step	Condition	Result	Action Taken	Response Sent
1	user_signed_in? == true	True	redirect_to dashboard_path	HTTP 302 Redirect to /dashboard
2	N/A	N/A	Browser requests /dashboard	New request starts
3	N/A	N/A	New controller action runs	Depends on new action
4	user_signed_in? == false	False	render :login	HTTP 200 OK with login HTML

💡 Execution stops after sending either redirect or render response.

Variable Tracker

Variable	Start	After Step 1	After Step 4	Final
user_signed_in?	unknown	true or false	false if render branch	final boolean value

Key Moments - 2 Insights

Why does redirect_to cause a new request instead of rendering a view?

redirect_to sends an HTTP 302 response telling the browser to load a new URL, so the current request ends and a new one begins (see execution_table steps 1 and 2).

Can you call render and redirect_to in the same controller action?

No, calling redirect_to or render ends the response immediately. The code after them won't run (see execution_table where only one action sends a response).

Visual Quiz - 3 Questions

Look at the execution table, what response is sent when user_signed_in? is true?

A No response sent

B HTTP 200 OK with login HTML

C HTTP 302 Redirect to /dashboard

D HTTP 404 Not Found

💡 Hint

Check step 1 in the execution_table where user_signed_in? is true.

At which step does the browser make a new request after redirect?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at execution_table step 2 describing the browser requesting the new URL.

If user_signed_in? is false, what action does the controller take?

A Render the login template

B Raise an error

C Redirect to dashboard_path

D Do nothing

💡 Hint

See execution_table step 4 where render :login is called.

Concept Snapshot

redirect_to sends an HTTP redirect response causing the browser to request a new URL.
render sends an HTTP response with a view template without a new request.
Only one of redirect_to or render should be called per controller action.
redirect_to ends the current request; render displays a view immediately.
Use redirect_to for navigation, render for showing views in the same request.

Full Transcript

In Rails controllers, you can either redirect or render in an action. Redirect sends a 302 HTTP response telling the browser to load a new URL, which starts a new request cycle. Render sends an HTML response directly without a new request. The controller decides based on conditions like user login status. Only one of redirect_to or render should be called per action because both end the response. Redirect causes the browser to make a new request, while render shows a view immediately. This flow helps control user navigation and page display in web apps.

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