Question

Rails 5.2，Postgres 10.4

新手。我有一个has_many：through关系，我正在尝试加入，但是，尽管有我的定义，Rails似乎使用了错误的外键。

用户将通过机会注册来注册许多机会。一个机会可能会吸引许多用户。

opportunity.rb

class Opportunity < ApplicationRecord
  has_many :opportunity_enrolment, :class_name => 'OpportunityEnrolment', :foreign_key => "opportunity_id"
  has_many :volunteers, through: :opportunity_enrolment, :foreign_key => "opportunity_id"
end

opportunity_enrolment.rb

class OpportunityEnrolment < ApplicationRecord
  has_many :opportunities, foreign_key: "id"
  has_many :volunteers, foreign_key: "id"
end

users.rb

class Volunteer < ApplicationRecord
  has_many :opportunity_enrolment, :class_name => 'OpportunityEnrolment', foreign_key: "volunteer_id"
  has_many :opportunities, through: :opportunity_enrolment, foreign_key: "opportunity_id"
end

在显示特定用户然后将该用户加入其机会时，由于连接创建不正确，我在机会表中获得了第一条记录。

<% @volunteer.opportunities.each do |volunteerenrolment| %>
  <table frame="box">
    <tr><td>Name: <%= volunteerenrolment.oppname %></td></tr> --Oppname is in the opportunities table.
    <tr><td>Created: <%= volunteerenrolment.created_at %></td></tr>
  </table>
<% end %>

Rails创建以下select语句。

SELECT "opportunities".* FROM "opportunities" INNER JOIN "opportunity_enrolments" ON "opportunities"."id" = "opportunity_enrolments"."id" WHERE "opportunity_enrolments"."volunteer_id" = $1

opportunity_enrolments.id是机会表中的主键。我需要我的应用代替加入aboveal_enrolments.opportunity_id，就像这样：

SELECT "opportunities".* FROM "opportunities" INNER JOIN "opportunity_enrolments" ON "opportunities"."id" = "opportunity_enrolments"."opportunity_id" WHERE "opportunity_enrolments"."volunteer_id" = $1

在我的生命中，我不知道Rails从哪里提取了错误的外键。我试图在模型中多次更改它，但是Rails似乎不在那儿。如果我使用.joins手动编写正确的select语句，那么一切正常，但是我希望与“约定优先于配置”保持一致

谢谢！

Answer 1

您的OpportunityEnrollment表是您的Opportunity和Volunteer类之间的粘合剂，实际上应该使用belongs_to。另外，您可以使用rails默认值来为您解释类名和外键。

也不要在名为“ users.rb”的文件中定义名为“ Volunteer”的类

opportunity.rb

class Opportunity < ApplicationRecord
  # note the plural below as per rails convention
  has_many :opportunity_enrolments
  has_many :volunteers, through: :opportunity_enrolments
end

opportunity_enrolment.rb

class OpportunityEnrolment < ApplicationRecord
  belongs_to :opportunity
  belongs_to :volunteer 
end

volunteer.rb

class Volunteer < ApplicationRecord
  has_many :opportunity_enrolments
  has_many :opportunities, through: :opportunity_enrolments
end

您的联接表应具有opportunity_id和volunteer_id字段。

Ruby on Rails-has_many通过join使用了错误的外键

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