扶手：无标识外键查找的ActiveRecord [英] Rails: Non id foreign key lookup ActiveRecord

问题描述

我想的ActiveRecord 来通过从表中的非ID列查找。 希望这是明确的，当我给你我的code样本。

I want ActiveRecord to lookup by a non-id column from a table. Hope this is clear when I give you my code sample.

class CoachClass < ActiveRecord::Base
  belongs_to :coach
end

class Coach < ActiveRecord::Base
    has_many :coach_classes, :foreign_key => 'user_name'
end

当我做了 coach_obj.coach_classes ，这正好触发

When I do a coach_obj.coach_classes, this rightly triggers

SELECT * FROM `coach_classes` WHERE (`coach_classes`.user_name = 2)

（2作为主教练的 ID 这里是我的问题。）

(2 being the that coach's id here which is my problem.)

我希望它触发

SELECT * FROM `coach_classes` WHERE (`coach_classes`.user_name = 'David')

（大卫作为主教练的用户名）

用户名是独一无二的，present两个表。

user_name is unique and present in both tables.

我不希望有一个 coach_id 在我的 coach_classes 表中的某些原因。

I do not want to have a coach_id in my coach_classes table for some reason.

推荐答案

我想你需要指定的关联主键选项，以及：

I think you need to specify the primary key options on the associations as well:

class CoachClass < ActiveRecord::Base 
  belongs_to :coach, :foreign_key => 'user_name', :primary_key => 'user_name'
end

class Coach < ActiveRecord::Base
  has_many :coach_classes, :foreign_key => 'user_name', :primary_key => 'user_name'
end 

本规定返回相关对象的主键的方式（默认为 ID ）。

This specifies the method that returns the primary key of the associated object (defaulting to id).

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