Simplest version of a cart that supports multiple orders.

app/models/cart.rb

@@ -0,0 +1,12 @@
+class Cart < ActiveRecord::Base
+  has_many :orders, :class_name => 'Spree::Order'
+  belongs_to :user, :class_name => Spree.user_class
+
+  def add_variant variant, quantity
+    if orders.empty?
+      order = Spree::Order.create
+      order.add_variant(variant, quantity)
+      orders << order
+    end
+  end
+end

app/models/spree/order_decorator.rb

@@ -3,6 +3,7 @@ require 'open_food_web/distribution_change_validator'
 Spree::Order.class_eval do
   belongs_to :order_cycle
   belongs_to :distributor, :class_name => 'Enterprise'
+  belongs_to :cart
 
   before_validation :shipping_address_from_distributor
   validate :products_available_from_new_distribution, :if => lambda { distributor_id_changed? || order_cycle_id_changed? }

db/migrate/20130807230834_add_cart.rb

@@ -0,0 +1,9 @@
+class AddCart < ActiveRecord::Migration
+  def change
+    create_table :carts do |t|
+      t.integer :user_id
+    end
+
+    add_column :spree_orders, :cart_id, :integer
+  end
+end

db/schema.rb

@@ -11,7 +11,11 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20130807002915) do
+ActiveRecord::Schema.define(:version => 20130807230834) do
+
+  create_table "carts", :force => true do |t|
+    t.integer "user_id"
+  end
 
   create_table "cms_blocks", :force => true do |t|
     t.integer  "page_id",    :null => false
@@ -447,6 +451,7 @@ ActiveRecord::Schema.define(:version => 20130807002915) do
     t.string   "currency"
     t.string   "last_ip_address"
     t.integer  "order_cycle_id"
+    t.integer  "cart_id"
   end
 
   add_index "spree_orders", ["number"], :name => "index_orders_on_number"

spec/models/cart_spec.rb

@@ -0,0 +1,32 @@
+require 'spec_helper'
+
+describe Cart do
+
+  describe "associations" do
+    it { should have_many(:orders) }
+  end
+
+  describe 'adding a product' do
+
+    let(:product) { create(:product) }
+
+    it 'when there are no orders in the cart, create one when a product is added' do
+      subject.add_variant product.master, 3
+
+      subject.orders.size.should == 1
+      subject.orders.first.line_items.first.product.should == product
+    end
+
+    it 'should create an order when a product from a new distributor is added'
+
+    it 'should create an order when a product from a new order cycle is added'
+
+    it 'should create line items in an order for added product, when in the same distributor'
+
+    it 'should create line items in an order for added product, when in the same distributor and order cycle'
+
+    it 'should not create line items in an order, if the product is in a different order cycle to the order'
+
+    it 'should not create line items in an order, if the product is in a different distributor to the order'
+  end
+end