Populating foreign key on create action

I have a Evaluation similar to this:

Evaluation.rb

has_one :cardio
has_one :neuro

Cardio.rb

belongs_to :evaluation

Neuro.rb

belongs_to :evaluation

My evaluation controller is similar to this:

  def create
    @patient = Patient.find(params[:id])
    @evaluator = Evaluator.find(session[:evaluator_id]) if session[:evaluator_id]
    @evaluation 开发者_如何学编程= Evaliation.new(:patient_id => @patient.id, :evaluator_id => @evaluator.id)
    @neuro = Neuro.new(:evaluation_id => @evaluation.id)
    @cardio = Cardio.new(:evaluation_id => @evaluation.id)
    if (@evaluation.save! && @neuro.save! && @cardio.save!)

      redirect_to evaluation_path(@evaluation.id), :notice => "Evaluation created"

    else
      render ("new") 
    end
  end

When the evaluation is created the cardio and neuro are created too, but with null evaluation_id. I tried to move the @cardio = Cardio.new(:evaluation_id => @evaluation.id) inside the if but it didnt worked too.

---

@evaluation won't have an id set until you save it, so @evaluation.id will be nil when you are creating @neuro and @cardio. In other words:

@evaluation = ...

if (@evaluation.save!)
  @neuro = Neuro.new(:evaluation_id => @evaluation.id)
  @cardio = Cardio.new(:evaluation_id => @evaluation.id)

  if (@neuro.save! && @cardio.save!)
    redirect_to evaluation_path(@evaluation.id), :notice => "Evaluation created"
  else
    render ("new")
  end

else
  render ("new") 
end