Rails:非 ID 外键查找 ActiveRecord [英] Rails: Non id foreign key lookup ActiveRecord

问题描述

我希望 ActiveRecord 通过表中的非 id 列进行查找.希望当我给你我的代码示例时，这很清楚.

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

当我做一个coach_obj.coach_classes，正确触发

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

(2 是那个教练的 id，这是我的问题.)

(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')

('David' 是那个教练的 user_name)

('David' being the that coach's user_name)

user_name 在两个表中都是唯一的.

user_name is unique and present in both tables.

出于某种原因，我不想在我的 coach_classes 表中有 coach_id.

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

推荐答案

我认为您还需要在关联上指定主键选项:

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 

指定返回关联对象主键的方法(默认为id).

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

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