When adding subsequent products, add valid products to cart

app/models/spree/order_decorator.rb

@@ -7,7 +7,7 @@ Spree::Order.class_eval do
   end
 
   def distributor=(distributor)
-    raise "You cannot change the distributor of an order with products" unless can_change_distributor?
+    raise "You cannot change the distributor of an order with products" unless distributor == self.distributor || can_change_distributor?
     super(distributor)
   end
 

app/views/spree/products/_add_to_cart.html.haml

@@ -13,6 +13,7 @@
       %p Distributor
       = select_tag "distributor_id", options_from_collection_for_select(@product.distributors, "id", "name", current_distributor.andand.id)
     - else
+      = hidden_field_tag "distributor_id", order.distributor.id
       .distributor-fixed= "Your distributor for this order is #{order.distributor.name}"
     %br/
     = button_tag :class => 'large primary', :id => 'add-to-cart-button', :type => :submit do

spec/models/order_spec.rb

@@ -10,7 +10,9 @@ describe Spree::Order do
   end
 
   it "raises an exception if distributor is changed without permission" do
-    p = build(:product)
+    d = build(:distributor)
+    p = build(:product, :distributors => [d])
+    subject.distributor = d
     subject.add_variant(p.master, 1)
     subject.can_change_distributor?.should be_false
 

spec/requests/consumer/add_to_cart_spec.rb

@@ -83,5 +83,25 @@ feature %q{
       page.should_not have_selector "button#add-to-cart-button"
       page.should have_content "Please complete your order at #{d1.name} before shopping with another distributor."
     end
+
+    it "adds products with valid distributors" do
+      # Given two products, each at the same distributor
+      d = create(:distributor)
+      p1 = create(:product, :distributors => [d])
+      p2 = create(:product, :distributors => [d])
+
+      # When I add the first to my cart
+      visit spree.product_path p1
+      click_button 'Add To Cart'
+
+      # And I add the second
+      visit spree.product_path p2
+      click_button 'Add To Cart'
+
+      # Then both should be in my cart
+      visit spree.cart_path
+      page.should have_selector 'h4 a', :text => p1.name
+      page.should have_selector 'h4 a', :text => p2.name
+    end
   end
 end