通过关联设置has_many

Question

I have 3 models

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 has attribute "code" (left_side || right_side) which determines BATTLE SIDE (there are always 2 sides in battles, coz always playing -- 1 vs. 1, team vs. team etc.)

I would like to specify association (left_side_video, right_side_video) in model video , which gets video for chosen side.

Now to get video for SIDE 1 (left) - use this code

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

I want to get my battle videos like this

Battle.first.left_side_video

I think, Battle model should look like this, but it doesnt work (works only left side)

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: Works, but not in desired way. The problem was in includes chain. model Battle has scope :all_inclusive , which loads all associations

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

Generated 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)

NOTICE THAT VIDEOS 2 AND 4 (FOR RIGHT SIDE) - dont load. I can access only 1,3 videos

Videos id, battle_id (side)

[1 , 1 (lft)]

[2 , 1 (rgt)]

[3 , 2 (lft)]

[4 , 2 (rgt)]

When I remove .includes(:right_side_video) from :all_inclusive chain I got this 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

Now this works fine. But IN SQL level - its not as perfect as I want. You can see, that videos 1, 3 are loaded in correct way

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

But video 2, 4 load by seperate sqls:

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

What I want? FINAL SQL GENERATED BY RUBY

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

Answer 1

Why don't you try with "joins" instead of "includes"?

You can create named_scope like this

    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'"
    }

Haven't tested this yet. But the perfect query should be more or less the similar one.

Answer 2

I think, you should use preload instead of includes for loading associations.

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

preload doesn't affect original query, it makes separate query for every association you specify.

It works great in rails 3.0.x. Dunno which version you use, it may differ...