Question

I’m working with the Agile Web Development with Rails (4th edition) book and I bumped into a piece of code that is not working. I tried hard to figure out why it’s not working, but I didn’t make it.

BACKGROUD INFORMATION

The following classes are involved:

class Cart < ActiveRecord::Base
  has_many :line_items, :dependent => :destroy
end

class LineItem < ActiveRecord::Base
  belongs_to :product
  belongs_to :cart
end

class ApplicationController < ActionController::Base
  protect_from_forgery

  private

  def current_cart
    Cart.find(session[:cart_id])
  rescue ActiveRecord::RecordNotFound
    cart = Cart.create
    session[:cart_id] = cart.id
  end
end

NOW
here is where it fails:

class LineItemsController < ApplicationController
  def index
    @line_items = LineItem.all`

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @line_items }
    end
  end

  # GET /line_items/1
  # GET /line_items/1.xml
  def show
    @line_item = LineItem.find(params[:id])

    respond_to do |format|
      format.html # show.html.erb
      format.xml  { render :xml => @line_item }
    end
  end

  # GET /line_items/new
  # GET /line_items/new.xml
  def new
    @line_item = LineItem.new

    respond_to do |format|
      format.html # new.html.erb
      format.xml  { render :xml => @line_item }
    end
  end

  # GET /line_items/1/edit
  def edit
    @line_item = LineItem.find(params[:id])
  end

  # POST /line_items
  # POST /line_items.xml
  def create
    @cart = current_cart
    product = Product.find(params[:product_id])
    @line_item = **@cart.line_items.build(:product => product)**`

ERROR MESSAGE
*NoMethodError in LineItemsController#create
undefined method `line_items’ for 9:Fixnum
Rails.root: /home/tmiskiew/depot*

*app/controllers/line_items_controller.rb:53:in `create’
Request
Parameters:
{“product_id”=>”4”,
“authenticity_token”=>”dR4nL5zI+R7qIIPwNkl3EoaI1KyFWRokvh92m3PwD8o=”}*

Anyone an idea what’s wrong with @cart.line_items.build?
I’m working rails 3.0.9 and ruby 1.8.7

Thanks
Thomas

Answer 1

Have a look at your error
undefined method line_items' for 9:Fixnum

This says that @cart is a number, not an Cart object (@cart = current_cart from create action returns a number),
current_cart function returns a number because
Cart.find(session[:cart_id]) returns recordNotFound and your rescue block from current_cart function will be executed.

Remember that every function in Ruby returns the result of the last executed line, so you will get returned the cart.id

Edit: For first comment, try to rewrite method

    def current_cart
      Cart.find(session[:cart_id])
      rescue ActiveRecord::RecordNotFound
        cart = Cart.create
        session[:cart_id] = cart.id
        cart # this will get returned
      end
    end