ruby-on-rails – 将复杂的has_many关系移植到Rails> 4.1(没

我正在将Rails应用程序移植到Rails 4.2.这个Rails应用程序在关联中包含一些相当复杂的手动SQL代码 – 部分是由于DB优化(例如子选择而不是JOIN),部分原因是由于在编写时没有可行的替代方案(Rails 3.0),部分原因是由于缺乏知识(我希望,至少 – 这很容易解决).

示例：InternalMessage类.可以在用户之间发送消息(InternalMessage的收件人和消息的“删除”,存储在InternalMessagesRecipients中,因为可以有几个)并且可以读取,回复,转发和删除它们.该关联看起来像这样：

class User < AR::Base
  has_many :internal_messages,:finder_sql => "SELECT DISTINCT(internal_messages.id),internal_messages.* FROM internal_messages " +
          ' LEFT JOIN internal_messages_recipients ON internal_messages.id=internal_messages_recipients.internal_message_id' +
          ' WHERE internal_messages.sender_id = #{id} OR internal_messages_recipients.recipient_id = #{id}',:counter_sql => 'SELECT count(DISTINCT(internal_messages.id)) FROM internal_messages ' +
          ' LEFT JOIN internal_messages_recipients ON internal_messages.id=internal_messages_recipients.internal_message_id' +
          ' WHERE internal_messages.sender_id = #{id} OR internal_messages_recipients.recipient_id = #{id}'
  # ...
end

关键部分是最后的“OR”子句 – 通过这种关联,我希望获得接收和发送的消息,这些消息与用户表单独连接：

has_many :sent_messages,-> { where(:sender_deleted_at => nil) },:class_name => 'InternalMessage',:foreign_key => 'sender_id' #,:include => :sender
  has_many :internal_messages_recipients,:foreign_key => 'recipient_id'
  has_many :rcvd_messages,:through => :internal_messages_recipients,:source => :internal_message,:class_name => 'InternalMessage'

因为InternalMessage可能有几个收件人(也可以自己发送给发件人).

问：如何将此finder_sql移植到兼容Rails 4.2的has_many定义？

def internal_messages
  InternalMessage.where( id: sent_message_ids + received_message_ids)
end