ruby-on-rails - attribute with multiple treatment (rails)

Question

I have a System class with an attr called price and a Subsystem class (belongs_to :system) with also this price attr.

The problem is in my model, because I have two different ways of treating the system.price

1) The system has at least one subsystem (!system.subsystems.empty?): I want the price to be the sum of all it's subsystems prices. In that case, my model has it's method price with a loop to sum the subsystems prices.

2) The system doesn't have ANY subsystem (system.subsystems.empty?): The price is simply an input field which it's filled in a form.

The trouble i'm facing is how to 'choose' which way to follow...

Can anyone help me? Thks a lot in advance!!!

Answer 1

您始终可以将系统的价格存储在其他地方，并在必要时选择使用它：

class System

  has_many :subsystems

  def price
    subsystems.empty? system_price : subsystems.sum('price')
  end

  def system_price
    # maybe an active record attribute, this method might not exist
    25.00
  end

end

Answer 2

您可以简单地覆盖模型中的价格方法：

def price
  if subsystems.empty? 
    self.attributes["price"] 
  else
    subsystems.map(&:price).sum
end