Question

When I’m at /profile/new, for example, and I submit a form to create a profile, Rails knows to perform a POST operation; and when I update that profile from /profile/edit/1, Rails knows to perform a PUT operation… My question is, how does it know to do that?

I can’t understand how this works past the controller. What exactly is going on in the background? I’ve dug around a little bit and I know ActiveRecord and ActiveResource? are involved, but I’d like to know the details. I’ve only been around since Rails 2.2 and every resource I find seems to teach by example. I’m interested in understanding how things work at a lower level, but there’s nothing to guide me through learning by reading apis & source code.

Answer 1

You know how a view page of new page or edit page in a user’s scaffold looks right?

form_for(@user) # something like that

So this is a helper method which you can find inside action_view/helper .. file

Basically the form rendering for new and edit will be decided by this form_for method, what this form_for method will do is (I just made some bullet points)

1) It will check what type of input you gave in your form_for
(check api for different ways of using form_for helper)
2) It will decide the the html options based on the below code

if object.respond_to?(:new_record?) && object.new_record? 
  { :class  => dom_class(object, :new),  :id => dom_id(object), :method => :post } # for new 
else
  { :class  => dom_class(object, :edit), :id => dom_id(object, :edit), :method => :put } # for edit
end

3) It will do one more thing for edit page it will add a hidden field which will have user’s id value in it.

Please let me know if you need some more details. I will update my answer accordingly.