Question

While learning Rails, I found this example in the Sam Ruby’s book:

app/controllers/line_items_controller.rb

def create
        @cart = current_cart
        product = Product.find(params[:product_id])
        @line_item = @cart.line_items.build
        @line_item.product = product

        respond_to do |format|
          if @line_item.save
            # this following line is strange for me 
            format.html { redirect_to(@line_item.cart, :notice => 'Line item was successfully created.') }
            format.xml  { render :xml => @line_item, :status => :created, :location => @line_item }
          else
            format.html { render :action => "new" }
            format.xml  { render :xml => @line_item.errors,
              :status => :unprocessable_entity }
          end
        end
  end

Why isn’t the section with redirect_to(@line_item.cart,...) merely replaced by redirect_to(@cart,...) ?

Indeed, @cart is an accessible instance variable.

Are we forced to use @line_item to retrieve cart in this example ?

Answer 1

Is there some sort of nested route involved in this example?
You could simply do a redirect_to @cart the example should still work.

Try it out. But it should work from my understanding. Maybe the author wanted to be a little bit more expressive in the whose cart he redirects to.