Rails 4: No double items in shopping app - ruby-on-rails

Question

building a shopping app but i don't want to show to listings of the same thing twice. I don't want it to show two listings for oranges. Instead I want it to show the quantity as 2.
I have changed the order_items_controller to show
#order_item = #order.order_items.find_or_initialize_by_product_id(params[:product_id])
#order_item.quantity += 1
get error undefined method `price' for nil:NilClass
tr>
<th>Order Total</th>
<td><%= print_price #order.total %></td> <- error
</tr>
<tr>
order_items.controller
class OrderItemsController < ApplicationController
before_action :set_order_item, only: [:show, :edit, :update, :destroy]
before_action :load_order, only: [:create]
# GET /order_items/1/edit
def edit
end
# POST /order_items
# POST /order_items.json
def create
#order_item = #order.order_items.find_or_initialize_by_product_id(params[:product_id])
respond_to do |format|
if #order_item.save
format.html { redirect_to #order, notice: 'Successfully Added Product To Cart.' }
format.json { render action: 'show', status: :created, location: #order_item }
else
format.html { render action: 'new' }
format.json { render json: #order_item.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /order_items/1
# PATCH/PUT /order_items/1.json
def update
respond_to do |format|
if #order_item.update(order_item_params)
format.html { redirect_to #order_item, notice: 'Order item was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: 'edit' }
format.json { render json: #order_item.errors, status: :unprocessable_entity }
end
end
end
# DELETE /order_items/1
# DELETE /order_items/1.json
def destroy
#order_item.destroy
respond_to do |format|
format.html { redirect_to #order_item.order }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_order_item
#order_item = OrderItem.find(params[:id])
end
def load_order
#order = Order.find_or_initialize_by_id(session[:order_id], status: "Unsubmitted")
if #order.new_record?
#order.save!
session[:order_id] = #order.id
end
end
# Never trust parameters from the scary internet, only allow the white list through.
def order_item_params
params.require(:order_item).permit(:product_id, :order_id, :quantity)
end
end
orders.show.html
class OrderItemsController < ApplicationController
before_action :set_order_item, only: [:show, :edit, :update, :destroy]
before_action :load_order, only: [:create]
# GET /order_items/1/edit
def edit
end
# POST /order_items
# POST /order_items.json
def create
#order_item = #order.order_items.find_or_initialize_by_product_id(params[:product_id])
respond_to do |format|
if #order_item.save
format.html { redirect_to #order, notice: 'Successfully Added Product To Cart.' }
format.json { render action: 'show', status: :created, location: #order_item }
else
format.html { render action: 'new' }
format.json { render json: #order_item.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /order_items/1
# PATCH/PUT /order_items/1.json
def update
respond_to do |format|
if #order_item.update(order_item_params)
format.html { redirect_to #order_item, notice: 'Order item was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: 'edit' }
format.json { render json: #order_item.errors, status: :unprocessable_entity }
end
end
end
# DELETE /order_items/1
# DELETE /order_items/1.json
def destroy
#order_item.destroy
respond_to do |format|
format.html { redirect_to #order_item.order }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_order_item
#order_item = OrderItem.find(params[:id])
end
def load_order
#order = Order.find_or_initialize_by_id(session[:order_id], status: "Unsubmitted")
if #order.new_record?
#order.save!
session[:order_id] = #order.id
end
end
# Never trust parameters from the scary internet, only allow the white list through.
def order_item_params
params.require(:order_item).permit(:product_id, :order_id, :quantity)
end
end
order.rb
class Order < ActiveRecord::Base
has_many :order_items, dependent: :destroy
def total
order_items.map(&:subtotal).sum
end
end
order_items.rb
class OrderItem < ActiveRecord::Base
belongs_to :order
belongs_to :product
validates :order_id, :product_id, presence: true
def subtotal
quantity * product.price
end
end
I have also created a table to add quantity
class AddDefaultQuantityToOrderItems < ActiveRecord::Migration
def change
change_column :order_items, :quantity, :integer, default: 0
end
end

Answer 1

The problem might be in your order model. You need 'self' to reference the current Order object. Change it to this
def total
self.order_items.map(&:subtotal).sum
end

Answer 2

In your create action for the order controller you need
#order = Order.find(<however you get the order id>)
you are trying to call a method on #order but you are not passing a value in the controller for that item as far as I can tell