Question

For example, I have something like this in my controller:

def save
  ...
  render 'error' if user.nil?
  @cast = user.cast
  render 'cast'
end

I have nil: no method error here (in user.cast). But if I use redirect_to instead of render, everything works perfectly.

It seems like Rails doesn’t stop their executive stack after render, but stops after redirect_to. Doesn’t it?

Answer 1

Your assumption is correct. redirect_to sends an HTTP 302 redirect message to the user’s browser, telling it to go to a different URL, thus stopping your current execution.

I’d reccommend checking out this post: http://blog.markusproject.org/?p=3313

He gives a great summary of how to use each:

render will render a particular view using the instance variables
available in the action. For example if a render was used for the new
action, when a user goes to /new, the new action in the controller is
called, instance variables are created and then passed to the new
view. Rails creates the html for that view and returns it back to the
user’s browser. This is what you would consider a normal page load.

redirect_to will send a redirect to the user’s browser telling it to
re-request a new URL. Then the browser will send a new request to that
URL and it will go through the action for that URL, oblivious to the
fact that it was redirected to. None of the variables created in the
action that caused the redirect will be available to the redirected
view. This is what happens when you click on ‘Create’ in a form and
the object is created and you’re redirected to the edit view for that
object.