如何从嵌套模型引用高级模型？

Question

我正在尝试根据付款模型中的项目状态进行条件验证。例如，状态可以是“对话”或“活动”。考虑到下面的结构，最好的方法是什么？

class Project < ActiveRecord::Base
  has_many :costs, :dependent => :destroy
  has_many :payments, :through => :costs, :dependent => :destroy
  accepts_nested_attributes_for :costs, :allow_destroy => true
end
class Cost < ActiveRecord::Base
  has_many :payments, :dependent => :destroy
  accepts_nested_attributes_for :payments, :allow_destroy => true
  belongs_to :project
end
class Payment < ActiveRecord::Base
  belongs_to :cost
  validates_presence_of :value1, :if => :new?
  validates_presence_of :value1, :if => :talks?
  validates_presence_of :value2, :if => :active?

  def new?
    # if controller action is new
  end
  def talks?
    # if project status is "Talks" (edit action)
  end
  def active?
    # if project status is "Active" (edit action)
  end
end

Answer 1

class Payment < ActiveRecord::Base
  belongs_to :cost
  has_one :project, :through => :cost
  validates_presence_of :value1, :if => :new?
  validates_presence_of :value1, :if => :talks?
  validates_presence_of :value2, :if => :active?

  def new?
    self.new_record?
  end
  def talks?
    project.status == "talks"
  end
  def active?
    project.status == "active"
  end
end