ruby on rails - Why is it normal for render to be called in both the controller and in the view? -

the rails guide layouts , rendering in rails gives examples of render being used in both controller , view.

the section rendering default ... mentions rendering called default. section using render gives example of render being called within controller:

def update   @book = book.find(params[:id])   if @book.update(book_params)     redirect_to(@book)   else     render "edit"   end end 

the section using partials gives example of render being used within view, example use partials.

<%= render "menu" %> 

neither cases of render being used in controller, nor case of render being used in view, strike me illogical. what's confusing me thought 1 of major concepts of rails model view controller separation, means giving separate responsibilities model, view, , controller.

why normal render called in both controller , in view?

i'd if used properly, when render used in view, should organization/structural tool in order make code view more understandable , readable.

when used in controller, it's defining entry point view , primary association between action in controller , view.

the difference subtle.