Rails server saying rollback transcation when clicking add to cart

Just started learning ruby on rails, and i created a simple shopping cart application but when i click "add to cart", i get a rollback transaction from my server. I believe the error has something to do with my orderitem controller but not sure how to fix this issue here my code.

---

rails server

Started POST "/order_items" for 127.0.0.1 at 2017-10-25 10:47:44 -0400
Processing by OrderItemsController#create as JS
  Parameters: {"utf8"=>"✓", "order_item"=>{"product_id"=>"13", "quantity"=>"1"}, "commit"=>"Add to cart"}
   (0.0ms)  begin transaction
  Product Load (0.5ms)  SELECT  "products".* FROM "products" WHERE "products"."id" = ? LIMIT ?  [["id", 13], ["LIMIT", 1]]
   (0.0ms)  rollback transaction
  Rendering order_items/create.js.erb
  Rendered order_items/create.js.erb (0.5ms)
Completed 200 OK in 1028ms (Views: 605.5ms | ActiveRecord: 0.5ms)

---

order_items_controller.rb

class OrderItemsController < ApplicationController

    def create
        @order = current_order
        @order_item = @order.order_items.new(order_item_params)
        @order.save
        session[:order_id] = @order.id
    end

    def update
        @order = current_order
        @order_item = @order.order_items.new(order_item_params)
        @order_item.update_attributes(order_item_params)
        @order_items = @order.order_items
    end

    def destroy
        @order = current_order
        @order_item = @order.order_items.find(params[:id])
        @order_item.destroy
        @order_items = @order.order_items
    end


    private

    def order_item_params
        params.require(:order_item).permit(:product_id, :quantity)
    end

end

---

create.js.erb

<% if @order.errors.any? || @order_item.errors.any? %>
    alert("Invalid")
<% else %>
    $(".cart").html("<%= escape_javascript(render 'layouts/cart') %>")
<% end %>

---

schema.rb

ActiveRecord::Schema.define(version: 20171019015705) do

  create_table "order_items", force: :cascade do |t|
    t.integer  "product_id"
    t.integer  "order_id"
    t.integer  "quantity"
    t.float    "total_price"
    t.float    "unit_price"
    t.datetime "created_at",  null: false
    t.datetime "updated_at",  null: false
  end

  create_table "orders", force: :cascade do |t|
    t.float    "subtotal"
    t.float    "total"
    t.float    "shipping"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.integer  "user_id"
  end

  create_table "products", force: :cascade do |t|
    t.string   "name"
    t.datetime "created_at",  null: false
    t.datetime "updated_at",  null: false
    t.float    "price"
    t.text     "description"
    t.string   "picture"
  end

  create_table "users", force: :cascade do |t|
    t.string   "email",                  default: "", null: false
    t.string   "encrypted_password",     default: "", null: false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          default: 0,  null: false
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
    t.string   "username"
    t.datetime "created_at",                          null: false
    t.datetime "updated_at",                          null: false
    t.index ["email"], name: "index_users_on_email", unique: true
    t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
  end

end