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Question

設置的has_many我有3個車型

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具有屬性 「代碼」（left_side || right_side），其確定BATTLE側（總有2個邊在戰鬥中，怎麼總是打 - 1對陣1，球隊vs.球隊等）

我想在模型視頻中指定關聯（left_side_video，right_side_video），它可以獲得選定球隊的視頻。

我們獲得SIDE 1（左）視頻 - 使用此代碼

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

我想我的戰鬥視頻這樣

Battle.first.left_side_video 

我認爲，對戰模式應該是這樣的，但它不工作（僅適用左側）

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 

UPDATE： 工程，但不是以所需的方式。問題出在includes鏈上。 模型Battle具有範圍:all_inclusive，它加載的所有關聯

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) 

注意到視頻2和4（FOR右側） - 不負載。我只能訪問1,3-視頻

畫 ID，battle_id（側面）

[1,1（LFT）]

[2，1（RGT）]

[ 3，2（LFT）]

[4,2（RGT）]

當我刪除.includes(:right_side_video)從:all_inclusive鏈我得到這個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 

現在，這工作正常。但是，在SQL級別 - 它不像我想要的那麼完美。你可以看到，視頻1,3加載正確的方式

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

但視頻2，4負載由單獨的sql語句：

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 

我想要什麼？ 生成者RUBY

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

Answer 1

最終的SQL你爲什麼不嘗試用「加入」，而不是「包括」？

你可以這樣

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'" 
    } 

創建named_scope沒有測試呢。但完美的查詢應該或多或少是類似的。

Answer 2

我認爲，您應該使用preload而不是includes來加載關聯。

範圍：包容各方的，預緊（：battle_category，：賭注，：票，：left_side_video，：right_side_video）

preload不影響原來的查詢，它使您可以指定每個協會單獨的查詢。

它在rails 3.0.x中很好用。不知道你使用哪個版本，它可能會有所不同...