Question

我有3个模特

class Battle < ActiveRecord::Base
  has_many :battle_videos
  has_many :videos, :through => :battle_videos
  ...
end


class BattleVideo < ActiveRecord::Base
  belongs_to :battle
  belongs_to :video  
  validates :code, :presence => true
end

class Video < ActiveRecord::Base
  belongs_to :user, :foreign_key => :user_id, :class_name => "User"
  ...
end

BattleVideo有属性“code”（left_side || right_side）决定了BATTLE SIDE（在战斗中总是有2个方面，因为总是在玩 - 1对1，团队对团队等等。）

我想在模型视频中指定关联（left_side_video，right_side_video），它会为所选方提供视频。

现在获取SIDE 1（左）的视频 - 使用此代码

Battle.first.battle_videos.where("battle_videos.code = 'left_side'").first.video

我希望得到像我这样的战斗视频

Battle.first.left_side_video

我认为，战斗模型应该看起来像这样，但它不起作用（仅适用于左侧）

class Battle < ActiveRecord::Base
  has_many :battle_videos
  has_many :videos, :through => :battle_videos

  has_many :left_side_video, :through => :battle_videos, :source => :video, :conditions => ["battle_videos.code = 'left_side'"]
  has_many :right_side_video, :through => :battle_videos, :source => :video, :conditions => ["battle_videos.code = 'right_side'"]
end

更新工作，但不是想要的方式。问题发生在includes链中。模型Battle具有范围:all_inclusive，它加载所有关联

scope :all_inclusive, includes(:battle_category).includes(:bets).includes(:votes).includes(:left_side_video).includes(:right_side_video)

生成的SQL：

Battle Load (0.6ms)  SELECT `battles`.* FROM `battles` WHERE (battles.status = 1 AND valid_from < '2012-01-31 13:31:50' AND battles.valid_to > '2012-01-31 13:31:50') ORDER BY battles.id DESC
BattleCategory Load (0.1ms)  SELECT `battle_categories`.* FROM `battle_categories` WHERE `battle_categories`.`id` IN (1)
Bet Load (0.1ms)  SELECT `bets`.* FROM `bets` WHERE `bets`.`parent_type` = 'Battle' AND `bets`.`parent_id` IN (1, 2)
Vote Load (0.2ms)  SELECT `votes`.* FROM `votes` WHERE `votes`.`parent_type` = 'Battle' AND `votes`.`parent_id` IN (1, 2)
BattleVideo Load (0.1ms)  SELECT `battle_videos`.* FROM `battle_videos` WHERE `battle_videos`.`battle_id` IN (1, 2) AND (battle_videos.code = 'user_1')
Video Load (0.1ms)  SELECT `videos`.* FROM `videos` WHERE `videos`.`id` IN (1, 3)

注意视频2和4（右侧） - 请勿加载。我只能访问1,3个视频

画 id，battle_id（side）

[1,1（lft）]

[2,1（rgt）]

[3,2（lft）]

[4,2（rgt）]

当我从.includes(:right_side_video)链中删除:all_inclusive时，我得到了这个sql：

Battle Load (0.6ms)  SELECT `battles`.* FROM `battles` WHERE (battles.status = 1 AND valid_from < '2012-01-31 13:39:26' AND battles.valid_to > '2012-01-31 13:39:26') ORDER BY battles.id DESC
BattleCategory Load (0.1ms)  SELECT `battle_categories`.* FROM `battle_categories` WHERE `battle_categories`.`id` IN (1)
Bet Load (0.1ms)  SELECT `bets`.* FROM `bets` WHERE `bets`.`parent_type` = 'Battle' AND `bets`.`parent_id` IN (1,2)
Vote Load (0.2ms)  SELECT `votes`.* FROM `votes` WHERE `votes`.`parent_type` = 'Battle' AND `votes`.`parent_id` IN (1,2)
BattleVideo Load (0.3ms)  SELECT `battle_videos`.* FROM `battle_videos` WHERE `battle_videos`.`battle_id` IN (1,2) AND (battle_videos.code = 'left_side')
Video Load (0.1ms)  SELECT `videos`.* FROM `videos` WHERE `videos`.`id` IN (1, 3)
Video Load (0.2ms)  SELECT `videos`.* FROM `videos` INNER JOIN `battle_videos` ON `videos`.`id` = `battle_videos`.`video_id` WHERE `battle_videos`.`battle_id` = 1 AND (battle_videos.code = 'right_side') LIMIT 1
Video Load (0.1ms)  SELECT `videos`.* FROM `videos` INNER JOIN `battle_videos` ON `videos`.`id` = `battle_videos`.`video_id` WHERE `battle_videos`.`battle_id` = 2 AND (battle_videos.code = 'right_side') LIMIT 1

现在这很好用。但是在SQL级别 - 它不如我想要的那么完美。你可以看到，视频1,3以正确的方式加载

Video Load (0.1ms)  SELECT `videos`.* FROM `videos` WHERE `videos`.`id` IN (1, 3)

但视频2,4由单独的sqls加载：

Video Load (0.2ms)  SELECT `videos`.* FROM `videos` INNER JOIN `battle_videos` ON `videos`.`id` = `battle_videos`.`video_id` WHERE `battle_videos`.`battle_id` = 1 AND (battle_videos.code = 'right_side') LIMIT 1
Video Load (0.1ms)  SELECT `videos`.* FROM `videos` INNER JOIN `battle_videos` ON `videos`.`id` = `battle_videos`.`video_id` WHERE `battle_videos`.`battle_id` = 2 AND (battle_videos.code = 'right_side') LIMIT 1

我想要什么？ RUBY生成的最终SQL

Video Load (0.1ms)  SELECT `videos`.* FROM `videos` WHERE `videos`.`id` IN (1, 2, 3, 4)

Answer 1

为什么不尝试使用“加入”而不是“包含”？

您可以像这样创建named_scope

    named_scope : left_side_video, {
      :select => "videos.*",
      :joins => "INNER JOIN battle_videos ON battle_videos.video_id = videos.id INNER JOIN battles on battles.id = battle_videos.battle_id", 
      :conditions=>"battle_videos.code = 'left_side'"
    }

尚未测试过。但完美的查询应该或多或少是类似的。

Answer 2

我认为，您应该使用preload代替includes来加载关联。

范围：all_inclusive，preload（：battle_category，：bets，：votes，：left_side_video，：right_side_video）

preload不会影响原始查询，它会对您指定的每个关联进行单独查询。

它在rails 3.0.x中运行良好。 Dunno你使用哪个版本，它可能会有所不同......

通过关联设置has_many

2 个答案: