Are redirect_to and render exchangeable?

Question

For the code below, what happens if replacing redirect_to with render or vise verse?

def create   @product = Product.new(params[:product])    respond_to do |format|     if @product.save       format.html { redirect_to(@product, :notice => 'Product was successfully created.') }      else       format.html { render :action => "new" }     end   end end 

It seems OK replacing one with the other in code above. Is there a place where only redirect_to or render has to be used? Render does nothing but rendering a view. Redirect_to sends 302 request to server and current parameters are lost after redirecting.

Thanks.

Answer 1

If you're using render, when the user refreshes the page, it will submit the previous POST request again. This may cause undesired results like duplicate purchase and others.

But if you're using redirect_to, when the user refreshes the page, it will just request that same page again. This is also known as the Post/Redirect/Get (PRG) pattern.

So the place where redirect_to should be used is when you're doing a HTTP POST request and you don't want the user to resubmit the request when it's done (which may cause duplicate items and other problems).

In Rails, when a model fails to be saved, render is used to redisplay the form with the same entries that was filled previously. This is simpler because if you use redirect, you'll have to pass the form entries either using parameters or session. The side effect is that if you refresh the browser, it will try to resubmit the previous form entries. This is acceptable because it will probably fail the same way, or if it's successful now, it was what the user should expect in the first place anyway.

For more in depth explanation about render and redirect, you should read this article.

Answer 2

When you redirect you will generate a new request that hits a controller method, render just renders the associated view. You use render in the create because you want to keep the state of the model object if the save fails so that you can render info about its errors. If you tried to redirect to the new_product path you would create a new model object and loose all the form data the user entered and any errors etc etc

EDIT (with some more info):

An example of a situation where you MUST use redirect_to is if your view template uses instance variables that are not initialized in the controller method you are redirecting from. So you probably could not call render {:action => 'index'} in your create method because the index template probably makes use of a @products variable but your only initialized @product so it would cause an exception