Rails范围和连接

问题描述

我已经尝试了所有我认为可以解决的问题，但没有发现任何问题。

I have tried everything i thought would work for this and am turning up nothing.

在轨道3中，我需要找到所有在车上装有CD播放器的用户。汽车有一个用户和一个收音机，一个用户属于汽车，收音机有很多汽车。

in rails 3, I need to find all users with a cd player in their car. A car has one user and one radio, and a user belongs to a car, and a radio has many cars.

我正在为如何通过以下方式执行此搜索而烦恼用户模型中的范围。

I am stumbling on how I would perform this search via a scope in the user model.

class User
  belongs_to :car

class Car
  belongs_to radio
  has_one :user, :dependent => destroy

class Radio
  has_many :cars

推荐答案

我假设您的意思是：
汽车有 radio_id ，用户有 car_id ，
，因为收音机有很多汽车，汽车有一个用户。带有外键的表始终位于关系的belongs_to末端。

I am assuming that you mean this:Car has radio_id, User has car_id,since a radio has many cars and car has one user. The table with the foreign key always is on the belongs_to end of the relationship.

在不真正知道您要查找的结构的情况下，应执行以下操作：

Without really knowing the structure you're looking for, something like the following should work:

scope :with_cd_player, joins(:cars).where('cars.radio_id is not null')

如果收音机中有一个类别列，则可以进行以下操作。

if there is a category column on the radio, the following would work.

scope :with_cd_player, joins(:car => :radio).where('cars.radio_id is not null').where("radios.category = 'cd_player'")

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