ruby on rails active record after_save not capturing the parent object

Question

I am trying to use after_save call back on cartItems object to update the total cart price attribute in the cart object (parent of cartItems) . But I am getting the error

undefined method cart_items on nil class

I researched on google and the code seems to be correct. However I am not able to execute it. Below are the contents of both cart and cart_items model. Please help !

cart.rb

class Cart < ActiveRecord::Base
  has_many :cart_items
  belongs_to :user
end

cart_item.rb

class CartItem < ActiveRecord::Base
 belongs_to :cart
 after_save :update_cart_total_and_tax_amount

 private
 def update_cart_total_and_tax_amount
  cartTotal=0
  applicableTax=0
  self.cart.cart_items.each do|cartItem|
    cartTotal = cartTotal + cartItem.inr_amount
  end
  cart.cart_total=cartTotal
  tax = Tax.find(1)
  totalTax = ( cartTotal * percentage_tax ) / 100
  if totalTax < tax.minimum_tax
    applicableTax=tax.minimum_tax
  else
    applicableTax = totalTax
  end
  cart.tax_amount = applicableTax
   cart.save
  end
 end

Answer 1

You don't need the self in the line

self.cart.cart_items.each do|cartItem|