Rails - 通过 has_many 关联搜索

Question

我有这些模型：

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种服务 - 尝试这样做：

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

但是由于使用模型关联错误，此查询不起作用。

我如何知道当前的汽车是否有一些安全气囊？

提前谢谢你。

Answer 1

假设你的迁移没问题

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

好吧，从关系的角度来看，我假设car_services是cars和car_service_definitions的丰富连接表

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

然后如果你要找安全气囊，就是这个样子

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