mysql - 将两个几乎相同的表作为一个模型处理

Question

我正在为位于维基媒体实验室的维基媒体数据库创建一些模型，由于技术问题，有两个表格需要修改。

一个表 revision 包含所有修订，但缺少用户名索引，因为它是一个由某些修订的空白用户名表达式组成的 View 。

另一个表 revision_userindex 有索引，但它缺少受空白影响的修订。

除此之外，它们是相同的，我希望能够将它用作一个单一模型，而不是将索引的低级细节传递给用户。

目前我有以下代码:

class Revision < ActiveRecord::Base
  self.table_name = :revision_userindex # or :revision
  self.primary_key = :rev_id

  has_many :externallinks, :class_name => 'Externallink', :foreign_key => :el_from    
  has_many :iwlinks, :class_name => 'Iwlink', :foreign_key => :iwl_from    
  has_many :langlinks, :class_name => 'Langlink', :foreign_key => :ll_from    
  has_many :pagelinks, :class_name => 'Pagelink', :foreign_key => :pl_from    
  has_many :recentchanges, :class_name => 'Recentchange', :foreign_key => :rc_this_oldid    
  belongs_to :page, :class_name => 'Page', :foreign_key => :rev_page    
  belongs_to :user, :class_name => 'User', :foreign_key => :rev_user    
  has_many :templatelinks, :class_name => 'Templatelink', :foreign_key => :tl_from    
  has_many :texts, :class_name => 'Text', :foreign_key => :old_id    
end

但我不知道有什么方法可以根据是否在上下文中指定用户来动态设置 self.table_name。即

Revision.find_by_page("page")
Revision.find(nnn)
Revision.where(...) # where the query doesn't link to the user table
@page.revisions
# etc...

应该使用revision 表，并且

Revision.find_by_user("user")
@user.revisions

应该使用revision_userindex 表

如果这可以在不重新实现一半 AR 的情况下实现，我很乐意知道。

两个表的主键相同。

作为引用，这里是表格的定义:

第一次修订:

CREATE ALGORITHM=UNDEFINED DEFINER=`viewmaster`@`%` SQL SECURITY DEFINER VIEW `revision` AS
SELECT `enwiki`.`revision`.`rev_id` AS `rev_id`,
       `enwiki`.`revision`.`rev_page` AS `rev_page`,
       if((`enwiki`.`revision`.`rev_deleted` & 1),NULL,`enwiki`.`revision`.`rev_text_id`) AS `rev_text_id`,
       if((`enwiki`.`revision`.`rev_deleted` & 2),NULL,`enwiki`.`revision`.`rev_comment`) AS `rev_comment`,
       if((`enwiki`.`revision`.`rev_deleted` & 4),NULL,`enwiki`.`revision`.`rev_user`) AS `rev_user`,
       if((`enwiki`.`revision`.`rev_deleted` & 4),NULL,`enwiki`.`revision`.`rev_user_text`) AS `rev_user_text`,
       `enwiki`.`revision`.`rev_timestamp` AS `rev_timestamp`,
       `enwiki`.`revision`.`rev_minor_edit` AS `rev_minor_edit`,
       `enwiki`.`revision`.`rev_deleted` AS `rev_deleted`,
       if((`enwiki`.`revision`.`rev_deleted` & 1),NULL,`enwiki`.`revision`.`rev_len`) AS `rev_len`,
       `enwiki`.`revision`.`rev_parent_id` AS `rev_parent_id`,
       if((`enwiki`.`revision`.`rev_deleted` & 1),NULL,`enwiki`.`revision`.`rev_sha1`) AS `rev_sha1`
FROM `enwiki`.`revision`

对于 revision_userindex:

CREATE ALGORITHM=UNDEFINED DEFINER=`viewmaster`@`%` SQL SECURITY DEFINER VIEW `revision_userindex` AS
SELECT `enwiki`.`revision`.`rev_id` AS `rev_id`,
       `enwiki`.`revision`.`rev_page` AS `rev_page`,
       if((`enwiki`.`revision`.`rev_deleted` & 1),NULL,`enwiki`.`revision`.`rev_text_id`) AS `rev_text_id`,
       if((`enwiki`.`revision`.`rev_deleted` & 2),NULL,`enwiki`.`revision`.`rev_comment`) AS `rev_comment`,
       `enwiki`.`revision`.`rev_user` AS `rev_user`,
       `enwiki`.`revision`.`rev_user_text` AS `rev_user_text`,
       `enwiki`.`revision`.`rev_timestamp` AS `rev_timestamp`,
       `enwiki`.`revision`.`rev_minor_edit` AS `rev_minor_edit`,
       `enwiki`.`revision`.`rev_deleted` AS `rev_deleted`,
       if((`enwiki`.`revision`.`rev_deleted` & 1),NULL,`enwiki`.`revision`.`rev_len`) AS `rev_len`,
       `enwiki`.`revision`.`rev_parent_id` AS `rev_parent_id`,
       if((`enwiki`.`revision`.`rev_deleted` & 1),NULL,`enwiki`.`revision`.`rev_sha1`) AS `rev_sha1`
FROM `enwiki`.`revision`
WHERE ((`enwiki`.`revision`.`rev_deleted` & 4) = 0)

Answer 1

只需将通用逻辑/配置放入一个 mixin 中，然后使用包含它的两个不同模型。像这样的东西(未经测试，但你明白了):

module RevisionCommon
 extend ActiveSupport::Concern

 included do

  has_many :externallinks, :class_name => 'Externallink', :foreign_key => :el_from    
  has_many :iwlinks, :class_name => 'Iwlink', :foreign_key => :iwl_from    
  has_many :langlinks, :class_name => 'Langlink', :foreign_key => :ll_from    
  has_many :pagelinks, :class_name => 'Pagelink', :foreign_key => :pl_from    
  has_many :recentchanges, :class_name => 'Recentchange', :foreign_key => :rc_this_oldid    
  belongs_to :page, :class_name => 'Page', :foreign_key => :rev_page    
  belongs_to :user, :class_name => 'User', :foreign_key => :rev_user    
  has_many :templatelinks, :class_name => 'Templatelink', :foreign_key => :tl_from    
  has_many :texts, :class_name => 'Text', :foreign_key => :old_id
 end

 module ClassMethods
  # if any
 end
end

class RevisionForPage < ActiveRecord::Base
  self.table_name = :revision_userindex # or :revision
  self.primary_key = :rev_id

  include RevisionCommon
end

class RevisionForUser < ActiveRecord::Base
  self.table_name = :revision_userindex # or :revision
  self.primary_key = :rev_user_id # or whatever
  include RevisionCommon
end