Question

我有这些模特：

class Car < ActiveRecord::Base
  has_many :car_services
end
class CarService < ActiveRecord::Base
  belongs_to :car
  belongs_to :car_service_definition
end
class CarServiceDefinition < ActiveRecord::Base
  has_many :car_services
end

我试图找出当前选择的汽车是否有某项服务 - 尝试这样做：

airbag = car.car_services.car_service_definitions.where('service_type = "Airbag"').first

但由于使用模型关联错误，此查询无法正常工作。

如果当前的汽车有一些安全气囊怎么办？

提前谢谢。

Answer 1

假设你的迁移很好

class Car < ActiveRecord::Base
  has_many :car_services
end
class CarService < ActiveRecord::Base
  belongs_to :car
  belongs_to :car_service_list
  has_and_belongs_to_many :car_service_definitions
end
class CarServiceDefinition < ActiveRecord::Base
end

airbag = car.car_services.car_service_definitions.where(service_type: 'AirBag').first

Answer 2

嗯，从关系的角度来看，我认为car_services是cars和car_service_definitions

的丰富联接表

您可以做的是在has_many :through和car上设置car_service_definition关系

class Car < ActiveRecord::Base
  has_many :car_services
  has_many :car_service_definitions, through: :car_services
end

class CarService < ActiveRecord::Base
  belongs_to :car
  belongs_to :car_service_definition
end

class CarServiceDefinition < ActiveRecord::Base
  has_many :car_services
  has_many :cars, through: :car_services
end

然后如果你想找到安全气囊，那就像这样

airbag = car.car_service_definitions.where("car_service_definitions.service_type" => 'AirBag').first

但是如果你想检查car是否有air_bag，可以写一个像这样的方法

class Car < ActiveRecord::Base
  def has_air_bag?
    car_service_definitions.where("car_service_definitions.service_type" => 'AirBag').count > 0
  end
end

Rails - 搜索has_many关联

2 个答案: