Question

我正在尝试创建一个结合了其他三种关系的关系。最初的三个都是同一个类，我喜欢像一个集团，但是我找不到一个很好的“arel”方式。

以下是我正在尝试做的一个例子。

有效的SQL查询是

SELECT `records`.* FROM `records` INNER JOIN `memberships` ON `records`.`subject_membership_id` = `memberships`.`id` OR `records`.`recorder_membership_id` = `memberships`.`id` OR `records`.`subject_membership_id` = `memberships`.`id` WHERE `memberships`.`group_id` = 4

当然，我想做那种rails方式。这是我到目前为止所拥有的。它应该是非常自我解释的，所以我不会浪费你的时间进一步解释它。

class Group < ActiveRecord::Base
  has_many :recorded_records, :through => :memberships, :source => :recorded_records, :class_name => "Record"
  has_many :reported_records, :through => :memberships, :source => :reported_records, :class_name => "Record"
  has_many :reviewed_records, :through => :memberships, :source => :reviewed_records, :class_name => "Record"

  #has_many :records through recorded_records, reported_records, reviewed_records??
  # Psuedo code above... Wondering how best to do this. I've tried...
  def records
    recorded_records | reported_records | reviewed_records
  end

  # But that makes three seperate database queries when what I really want is...
  # SELECT `records`.* FROM `records` INNER JOIN `memberships` ON `records`.`subject_membership_id` = `memberships`.`id` OR `records`.`recorder_membership_id` = `memberships`.`id` OR `records`.`subject_membership_id` = `memberships`.`id` WHERE `memberships`.`group_id` = 4

end

你们摇滚！谢谢:)）

Answer 1

您可以使用自定义联接执行此操作。使用上面的SQL：

Record.joins('INNER JOIN `memberships` ON `records`.`subject_membership_id` = `memberships`.`id` OR `records`.`recorder_membership_id` = `memberships`.`id` OR `records`.`subject_membership_id` = `memberships`.`id` WHERE `memberships`.`group_id` = 4')

通过一些工作，您可以将其添加为模型中的方法，使其接受参数等。

Railsguide here提供了一些使用.join

的示例

Answer 2

确定！嘿，非常感谢你的帮助，@ RiPuk。你激发了我的观点。我所做的是从select语句中创建一个视图：

AS SELECT
  `records`.`id` AS `record_id`,
  `memberships`.`group_id` AS `group_id`
FROM (`records` join `memberships`) where ((`records`.`subject_membership_id` = `memberships`.`id`) or (`records`.`recorder_membership_id` = `memberships`.`id`) or (`records`.`subject_membership_id` = `memberships`.`id`));

我将此视图命名为view_group_records，然后创建了一个名为GroupRecord的ActiveRecord模型（具有适当的关系），现在在我的Group模型中，我与GroupRecord建立了has_many关系，然后{has_many :records, :through => :group_records 1}}。

这似乎运作良好！

但你的解决方案绝对有效。

Ruby on Rails：创建一个结合了三个其他关系的关系

2 个答案: