Question

In LessonsController, there are new and create methods.

def new
  @lesson = Lesson.new
end

def create
  @lesson = Lesson.new(params[:lesson])
  if @lesson.save do something end
end

I’ve been doing this in my apps without giving a thought. It works, but I’m confused why I am creating the instance variable both in the new and create action. From what I understand, this is the flow:

When a user clicks the new lesson button, he will be directed to LessonsController#new. When he puts in the required value and click submit he will be directed to LessonsController#create. I haven’t needed a view template for the create method.

So my confusion is, why are you creaing @lesson object again in the create method? I think the answer to this question might have to involve some concepts about GET and POST HTTP methods as well.

I appreciate any help! Thank you.

Answer 1

This is because HTTP is a sessionless protocol and any instance variables are not carried over between multiple requests.

A request to load up the #new page is a single request and once you submit the form and hit create button (or any of it’s other counterpart) The browsers initiates a new request to your #create method.

The first time around in #new method – You are creating an instance variable @lesson with it’s default values:

@lesson = Lesson.new

However, the second time around in #create method – The new request is forcing to create a very different instance variable:

@lessong = Lesson.new(params[:lesson])

This ^ second time around you are initiating the instance variable with the values received from the form submit (usually a POST request with #create). I hope that clears any air with why it is this way.