#new without any parameters

lib/has_aux_table.rb

@@ -253,11 +253,16 @@ module HasAuxTable
     sig { params(config: AuxTableConfig).void }
     def setup_initialize_hook!(config)
       initialize_method = self.instance_method(:initialize)
-      self.define_method(:initialize) do |args, **kwargs, &block|
+      self.define_method(:initialize) do |*args, **kwargs, &block|
         T.bind(self, ActiveRecord::Base)
-        main_args, aux_args = config.aux.partition_by_columns(args)
-        initialize_method.bind(self).call(main_args, **kwargs, &block)
-        config.aux_model_for(self).assign_attributes(aux_args)
+        if args && args.size == 1 && (arg = args.first).is_a?(Hash)
+          main_args, aux_args = config.aux.partition_by_columns(args.first)
+          initialize_method.bind(self).call(main_args, **kwargs, &block)
+          config.aux_model_for(self).assign_attributes(aux_args)
+        else
+          initialize_method.bind(self).call(*args, **kwargs, &block)
+          config.aux_model_for(self)
+        end
       end
     end
 

spec/active_record/has_aux_table_spec.rb

@@ -51,6 +51,16 @@ RSpec.describe HasAuxTable do
     end
   end
 
+  it "can be created with .new" do
+    car = Car.new
+    car.name = "Honda Civic"
+    car.engine_size = 1.8
+    car.save!
+    expect(car.fuel_type).to be_nil
+    expect(car.engine_size).to eq(1.8)
+    expect(car.name).to eq("Honda Civic")
+  end
+
   it "has the right #attributes" do
     car =
       Car.create!(name: "Honda Civic", fuel_type: "gasoline", engine_size: 2.0)