Do not add the product to cart if the user specifies a distributor that the product is not available at

app/controllers/spree/orders_controller_decorator.rb

@@ -3,9 +3,26 @@ Spree::OrdersController.class_eval do
 
   def populate_order_distributor
     @distributor = Spree::Distributor.find params[:distributor_id]
-    if @distributor.nil?
-      return false
-    end
 
+    redirect_to cart_path unless populate_valid? @distributor
+  end
+
+  private
+  def populate_valid? distributor
+    # -- Distributor must be specified
+    return false if distributor.nil?
+
+    # -- All products must be available under that distributor
+    params[:products].each do |product_id, variant_id|
+      product = Spree::Product.find product_id
+      return false unless product.distributors.include? distributor
+    end if params[:products]
+
+    params[:variants].each do |variant_id, quantity|
+      variant = Spree::Variant.find variant_id
+      return false unless variant.product.distributors.include? distributor
+    end if params[:variants]
+
+    true
   end
 end

spec/controllers/orders_controller_spec.rb

@@ -2,7 +2,7 @@ require 'spec_helper'
 
 describe Spree::OrdersController do
   context "adding the first product to the cart" do
-    it "does nothing if the user does not specify a distributor" do
+    it "does not add the product if the user does not specify a distributor" do
       create(:distributor)
       p = create(:product)
 
@@ -10,5 +10,15 @@ describe Spree::OrdersController do
         spree_put :populate, :variants => {p.id => 1}
       end.to change(Spree::LineItem, :count).by(0)
     end
+
+    it "does not add the product if the user specifies a distributor that the product is not available at" do
+      distributor_product = create(:distributor)
+      distributor_no_product = create(:distributor)
+      p = create(:product, :distributors => [distributor_product])
+
+      expect do
+        spree_put :populate, :variants => {p.id => 1}, :distributor_id => distributor_no_product.id
+      end.to change(Spree::LineItem, :count).by(0)
+    end
   end
 end