enhancement: Detect polymorphic associations in generator

lib/generators/avo/resource_generator.rb

@@ -185,11 +185,34 @@ def fields_from_model_tags
 
         def fields_from_model_associations
           associations.each do |name, association|
-            fields[name] = if association.is_a? ActiveRecord::Reflection::ThroughReflection
-              field_from_through_association(association)
-            else
-              ::Avo::Mappings::ASSOCIATIONS_MAPPING[association.class]
-            end
+            fields[name] =
+              if association.polymorphic?
+                field_with_polymorphic_association(association)
+              elsif association.is_a?(ActiveRecord::Reflection::ThroughReflection)
+                field_from_through_association(association)
+              else
+                ::Avo::Mappings::ASSOCIATIONS_MAPPING[association.class]
+              end
+          end
+        end
+
+        def field_with_polymorphic_association(association)
+          Rails.application.eager_load! unless Rails.application.config.eager_load
+
+          types = polymorphic_association_types(association)
+
+          {
+            field: "belongs_to",
+            options: {
+              polymorphic_as: ":#{association.name}",
+              types: types.presence || "[] # Types weren't computed correctly. Please configure them."
+            }
+          }
+        end
+
+        def polymorphic_association_types(association)
+          ActiveRecord::Base.descendants.filter_map do |model|
+            Inspector.new(model.name) if model.reflect_on_all_associations(:has_many).any? { |assoc| assoc.options[:as] == association.name }
           end
         end
 
@@ -293,5 +316,20 @@ def field(name, type)
         end
       end
     end
+
+    # This class modifies the inspect function to correctly handle polymorphic associations.
+    # It is used in the polymorphic_association_types function.
+    # Without modification: Model(id: integer, name: string)
+    # After modification: Model
+    class Inspector
+      attr_accessor :name
+      def initialize(name)
+        @name = name
+      end
+
+      def inspect
+        name
+      end
+    end
   end
 end

spec/features/avo/generators/resource_generator_spec.rb

@@ -46,6 +46,28 @@
       end
     end
   end
+
+  context "when generating resources with polymorphic associations" do
+    it "generates commented polymorphic fields" do
+      files = [
+        Rails.root.join("app", "avo", "resources", "review.rb").to_s,
+        Rails.root.join("app", "controllers", "avo", "reviews_controller.rb").to_s
+      ]
+
+      keeping_original_files(files) do
+        Rails::Generators.invoke("avo:resource", ["review", "-q", "-s"], {destination_root: Rails.root})
+
+        # Types load in different order every time
+        expect(File.read(files[0])).to include("field :reviewable, as: :belongs_to, polymorphic_as: :reviewable, types:")
+        expect(File.read(files[0])).to include("Team")
+        expect(File.read(files[0])).to include("Project")
+        expect(File.read(files[0])).to include("Post")
+        expect(File.read(files[0])).to include("Fish")
+
+        check_files_and_clean_up files
+      end
+    end
+  end
 end
 
 def keeping_original_files(files)