Product requires at least one distributor

app/models/spree/product_decorator.rb

@@ -3,4 +3,6 @@ Spree::Product.class_eval do
   has_and_belongs_to_many :distributors
 
   attr_accessible :supplier_id
+
+  validates_presence_of :distributors
 end

spec/models/product_spec.rb

@@ -7,4 +7,16 @@ describe Spree::Product do
     it { should have_and_belong_to_many(:distributors) }
   end
 
+  describe "validations" do
+    it "is valid when created from factory" do
+      Spree::Product.make.should be_valid
+    end
+
+    it "requires at least one distributor" do
+      product = Spree::Product.make
+      product.distributors.clear
+      product.should_not be_valid
+    end
+  end
+
 end

spec/support/blueprints.rb

@@ -35,6 +35,7 @@ Spree::Product.blueprint do
   available_on{ Date.today - 2.days }
   count_on_hand { 5 }
   price       { 10.99 }
+  distributors{[Spree::Distributor.first || Spree::Distributor.make]}
 end
 
 Spree::Variant.blueprint do