Raise error if distributor changed illegally

app/models/spree/order_decorator.rb

@@ -6,6 +6,11 @@ Spree::Order.class_eval do
     line_items.empty?
   end
 
+  def distributor=(distributor)
+    raise "You cannot change the distributor of an order with products" unless can_change_distributor?
+    super(distributor)
+  end
+
   # before_validation :shipping_address_from_distributor
 
   private

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

@@ -11,5 +11,7 @@
       %li.nowrap
         - if order.nil? || order.can_change_distributor?
           = link_to distributor.name, select_distributor_path(distributor)
+        - else
+          = distributor.name
     - if current_distributor && order.can_change_distributor?
       %li.nowrap= link_to 'Leave distributor', deselect_distributors_path

spec/controllers/distributors_controller_spec.rb

@@ -40,8 +40,8 @@ describe Spree::DistributorsController do
       d2 = create(:distributor)
       p = create(:product, :distributors => [d1])
       o = current_order(true)
-      o.add_variant(p.master, 1)
       o.distributor = d1
+      o.add_variant(p.master, 1)
       o.save!
 
       # When I attempt to select a distributor
@@ -57,8 +57,8 @@ describe Spree::DistributorsController do
       d = create(:distributor)
       p = create(:product, :distributors => [d])
       o = current_order(true)
-      o.add_variant(p.master, 1)
       o.distributor = d
+      o.add_variant(p.master, 1)
       o.save!
 
       # When I attempt to deselect the distributor

spec/models/order_spec.rb

@@ -1,11 +1,21 @@
 require 'spec_helper'
 
 describe Spree::Order do
-  it "provides permissions for changing distributor" do
+  it "reveals permission for changing distributor" do
     p = build(:product)
 
     subject.can_change_distributor?.should be_true
     subject.add_variant(p.master, 1)
     subject.can_change_distributor?.should be_false
   end
+
+  it "raises an exception if distributor is changed without permission" do
+    p = build(:product)
+    subject.add_variant(p.master, 1)
+    subject.can_change_distributor?.should be_false
+
+    expect do
+      subject.distributor = nil
+    end.to raise_error "You cannot change the distributor of an order with products"
+  end
 end