allow multiple taxons on product creation

backend/app/controllers/spree/admin/products_controller.rb

@@ -8,6 +8,7 @@ class ProductsController < ResourceController
       before_action :load_data, except: [:index]
       update.before :update_before
       helper_method :clone_object_url
+      before_action :split_params, only: [:create, :update]
 
       def show
         redirect_to action: :edit
@@ -19,12 +20,6 @@ def index
       end
 
       def update
-        if params[:product][:taxon_ids].present?
-          params[:product][:taxon_ids] = params[:product][:taxon_ids].split(',')
-        end
-        if params[:product][:option_type_ids].present?
-          params[:product][:option_type_ids] = params[:product][:option_type_ids].split(',')
-        end
         if updating_variant_property_rules?
           params[:product][:variant_property_rules_attributes].each do |_index, param_attrs|
             param_attrs[:option_value_ids] = param_attrs[:option_value_ids].split(',')
@@ -73,6 +68,15 @@ def clone
 
       private
 
+      def split_params
+        if params[:product][:taxon_ids].present?
+          params[:product][:taxon_ids] = params[:product][:taxon_ids].split(',')
+        end
+        if params[:product][:option_type_ids].present?
+          params[:product][:option_type_ids] = params[:product][:option_type_ids].split(',')
+        end
+      end
+
       def find_resource
         Spree::Product.with_deleted.friendly.find(params[:id])
       end

backend/spec/controllers/spree/admin/products_controller_spec.rb

@@ -50,6 +50,26 @@
     end
   end
 
+  # regression test for https://github.com/spree/spree/issues/2791
+  context "adding taxons to a product" do
+    let(:product) { create(:product) }
+    let(:first_taxon) { create(:taxon) }
+
+    it "adds a single taxon to a product" do
+      put :update, params: { id: product.to_param, product: { taxon_ids: first_taxon.id.to_s } }
+      expect(flash[:success]).to eq("Product #{product.name.inspect} has been successfully updated!")
+    end
+
+    context "when there are mulitple taxons" do
+      let(:second_taxon) { create(:taxon) }
+
+      it "adds multiple taxons to a product" do
+        put :update, params: { id: product.to_param, product: { taxon_ids: "#{first_taxon.id}, #{second_taxon.id}" } }
+        expect(flash[:success]).to eq("Product #{product.name.inspect} has been successfully updated!")
+      end
+    end
+  end
+
   describe "creating variant property rules" do
     let(:first_property) { create(:property) }
     let(:second_property) { create(:property) }