Add errors when node cant be deleted

app/models/alchemy/node.rb

@@ -4,6 +4,8 @@ module Alchemy
   class Node < BaseRecord
     VALID_URL_REGEX = /\A(\/|\D[a-z\+\d\.\-]+:)/
 
+    before_destroy :check_if_related_essence_nodes_present
+
     acts_as_nested_set scope: "language_id", touch: true
     stampable stamper_class_name: Alchemy.user_class_name
 
@@ -75,5 +77,13 @@ def to_partial_path
     def view_folder_name
       "alchemy/menus/#{name.parameterize.underscore}"
     end
+
+    def check_if_related_essence_nodes_present
+      dependent_essence_nodes = self_and_descendants.flat_map(&:essence_nodes)
+      if dependent_essence_nodes.any?
+        errors.add(:base, :essence_nodes_present, page_names: dependent_essence_nodes.map(&:page).map(&:name).to_sentence)
+        throw(:abort)
+      end
+    end
   end
 end

config/locales/alchemy.en.yml

@@ -711,6 +711,10 @@ en:
   activerecord:
     errors:
       models:
+        alchemy/node:
+          attributes:
+            base:
+              essence_nodes_present: "This menu item is in use inside an Alchemy element on the following pages: %{page_names}."
         alchemy/site:
           attributes:
             languages:

spec/models/alchemy/node_spec.rb

@@ -135,4 +135,33 @@ module Alchemy
       end
     end
   end
+
+  describe "#destroy" do
+    context "if there are essence nodes present" do
+      let(:node) { create(:alchemy_node) }
+      let(:page) { create(:alchemy_page, :layoutpage, page_layout: :footer) }
+      let(:element) { create(:alchemy_element, name: "menu", page: page) }
+      let(:content) { create(:alchemy_content, name: "menu", element: element) }
+
+      before do
+        node.essence_nodes.create(content: content)
+      end
+
+      it "does not destroy the node but adds an error" do
+        node.destroy
+        expect(node).not_to be_destroyed
+        expect(node.errors.full_messages).to eq(["This menu item is in use inside an Alchemy element on the following pages: #{page.name}."])
+      end
+
+      context "if there are essence nodes present on a child node" do
+        let!(:parent_node) { create(:alchemy_node, children: [node]) }
+
+        it "does not destroy the node and children either but adds an error" do
+          parent_node.destroy
+          expect(parent_node).not_to be_destroyed
+          expect(parent_node.errors.full_messages).to eq(["This menu item is in use inside an Alchemy element on the following pages: #{page.name}."])
+        end
+      end
+    end
+  end
 end