Redirect and render in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when both redirect_to and render are called in a Rails controller action?

Consider this Rails controller action:

def example
  redirect_to root_path
  render :show
end

What will be the result when this action is called?

Ruby on Rails

def example
  redirect_to root_path
  render :show
end

A The action redirects to root_path and then renders the show template, so both happen.

B Rails ignores the render call and only performs the redirect_to.

C Rails ignores the redirect_to and only renders the show template.

D Rails raises a DoubleRenderError because you cannot call both redirect_to and render in the same action.

💡 Hint

Think about what Rails allows in a single controller action regarding response.

Rails does not allow both redirect_to and render to be called in the same action because it causes confusion about what response to send. It raises a DoubleRenderError.

❓ state_output

intermediate

What is the HTTP status code when using redirect_to in Rails without specifying status?

In a Rails controller, if you call redirect_to some_path without specifying a status, what HTTP status code is sent to the browser?

Ruby on Rails

redirect_to some_path

A 200 OK

B 301 Moved Permanently

C 302 Found (Temporary Redirect)

D 404 Not Found

💡 Hint

Think about the default redirect status Rails uses for redirect_to.

By default, redirect_to sends a 302 Found status, which means a temporary redirect.

📝 Syntax

advanced

Which option correctly renders a JSON response and then redirects in a Rails controller?

Given the following controller code, which option will NOT cause an error?

def example
  # your code here
end

Ruby on Rails

def example
  # your code here
end

A redirect_to root_path

B

render json: { message: 'Hello' }
redirect_to root_path

C

redirect_to root_path
render json: { message: 'Hello' }

D render json: { message: 'Hello' }

💡 Hint

Remember Rails only allows one response per action.

Calling both render and redirect_to in the same action causes a DoubleRenderError. Only one response is allowed. Options A and B call both, causing errors. Option A only renders JSON, which is valid. Option A only redirects, which is also valid. But the question asks which option will NOT cause an error when rendering JSON and then redirecting. Since you cannot do both, only option A is valid as it only renders JSON. Option A only redirects, which is also valid but does not render JSON.

🔧 Debug

advanced

Why does this Rails controller action raise a DoubleRenderError?

Look at this controller action:

def show
  if params[:format] == 'json'
    render json: { message: 'Hello' }
  end
  redirect_to root_path
end

Why does it raise a DoubleRenderError?

Ruby on Rails

def show
  if params[:format] == 'json'
    render json: { message: 'Hello' }
  end
  redirect_to root_path
end

A Because <code>redirect_to</code> is called after <code>render</code> without stopping execution.

B Because <code>render</code> is missing a status code.

C Because <code>redirect_to</code> cannot be used with JSON responses.

D Because the <code>if</code> condition is always true.

💡 Hint

Think about what happens after render is called.

After calling render, the action continues and calls redirect_to. Rails does not allow sending two responses, so it raises a DoubleRenderError. To fix, you must return or use elsif to avoid calling both.

🧠 Conceptual

expert

How does Rails decide what to do when both render and redirect_to are called conditionally in the same action?

Consider this controller action:

def index
  if params[:redirect]
    redirect_to root_path
  else
    render :index
  end
end

What will Rails do when params[:redirect] is true and when it is false?

Ruby on Rails

def index
  if params[:redirect]
    redirect_to root_path
  else
    render :index
  end
end

A Rails always renders the index template regardless of the condition.

B When true, Rails redirects; when false, Rails renders the index template. No errors occur.

C Rails raises a DoubleRenderError because both render and redirect_to exist in the action.

D Rails ignores the redirect_to and always renders the index template.

💡 Hint

Think about conditional flow and response in Rails actions.

Rails allows either render or redirect_to to be called once per action. Here, only one is called depending on the condition, so no error occurs.