Question

基于Rails指南中的一个示例（http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association），我编写了以下代码：

class Patient < ActiveRecord::Base
  has_many :appointments
  has_many :physicians, through: :appointments
end

class Appointment < ActiveRecord::Base
  belongs_to :physician
  belongs_to :patient
end

class Physician < ActiveRecord::Base
  has_many :appointments
  has_many :patients, through: :appointments

  def vips
    patients.where(appointments: { vip: true })
  end

  def add_vip patient
    appointments.create(patient: patient, vip: true)
  end

  def delete_vip patient
    vips.delete(patient)
  end
end

问题在于，如果我有一个physician（一个医生的实例）和一个patient，那么

physician.add_vip(patient)
physician.delete_vip(patient)

delete_vip不仅会删除关联，还会删除实例本身。

如何只删除关联？

Answer 1

您要删除的关联/记录是约会而非患者。您正在add_vip中创建约会，并且应该在delete_vip中删除约会。

# Deletes all appointments for that patient without destroying the patient itself.
def delete_vip patient
  appointments.where(patient: patient, vip: true).delete_all
end

Answer 2

你可以这样做（不仅仅是）：

def delete_vip patient
    Appointment.where(physician_id: self.id, patient_id: patient.id).first.destroy!
end

Rails 4：通过关联删除has_many

2 个答案: