bugfix 2 in add by barcode

app/controllers/pre_sales_controller.rb

@@ -101,8 +101,12 @@ class PreSalesController < ApplicationController
         format.js { render action: "create" }
       else
         total_in_pre_sales = PreSale.where(user_id: current_user.id).sum(:total)
-        @pre_sale = PreSale.new(customer_id: params[:customer_id], user_id: current_user.id, open_cash_register_id: params[:open_cash_register_id], product_id: @product.id, sale_type: params[:sale_type], quantity: 1)
-
+        @pre_sale = PreSale.find_by(product_id: @product.id, user_id: current_user.id)
+        if @pre_sale.present? # si ya existe un pre sale con ese producto
+          @pre_sale.quantity += 1
+        else
+          @pre_sale = PreSale.new(customer_id: params[:customer_id], user_id: current_user.id, open_cash_register_id: params[:open_cash_register_id], product_id: @product.id, sale_type: params[:sale_type], quantity: 1)
+        end
         #precio unitario
         @pre_sale.unit_price = @pre_sale.product.get_price_sale(OpenCashRegister.find(@pre_sale.open_cash_register_id).pointsale.id)
         @pre_sale.get_totals