Rails中的多級關聯

Question

我正在創建一個應用程序來跟蹤整個賽季的足球隊。 但我被困在數據庫的設計上。 一個裝置有一個主隊和一個客隊。 我創建了一個具有兩個外鍵的夾具模型-home_team和away_team，但是我無法使關聯正常工作。 有任何想法嗎？ 每個裝置都屬於一個聯賽。

Answer 1

簡單的答案是：

class Fixture < ActiveRecord::Base
  belongs_to :home_team, :class_name => "Team", :foreign_key => :home_team
  belongs_to :away_team, :class_name => "Team", :foreign_key => :away_team
end

class Team < ActiveRecord::Base
  has_many :fixtures
end

但這對您不利，因為Team.fixtures無法正常工作。

class Team < ActiveRecord::Base
  has_many :home_fixtures, :class_name => "Fixtures", :foreign_key => :home_team
  has_many :away_fixtures, :class_name => "Fixtures", :foreign_key => :away_team
end

將為您提供兩個集合…但是將它們匯總起來必須使用紅寶石進行，這非常危險。

class Team < ActiveRecord::Base
  def fixtures(*args)
    home_fixtures.all(*args) + away_fixtures.all(*args)
  end
end

這也有問題，排序和限制都將增加（嘿，雙關語，誰知道？）。

class Team < ActiveRecord::Base
  has_many :fixtures, :finder_sql => 'SELECT * FROM fixtures where (home_team = #{id} or away_team = #{id})'
  has_many :home_fixtures, :class_name => "Fixtures", :foreign_key => :home_team
  has_many :away_fixtures, :class_name => "Fixtures", :foreign_key => :away_team
end

這很丑陋，但可能會起作用。 finder_sql似乎可以完成所需的工作。

另一個選擇是使用named_scope：

class Fixture < ActiveRecord::Base
  named_scope :for_team_id, lambda{|team_id| {:conditions => ['(home_team = ? or away_team = ?)', team_id, team_id]} }
  belongs_to :home_team, :class_name => "Team", :foreign_key => :home_team
  belongs_to :away_team, :class_name => "Team", :foreign_key => :away_team
end

class Team < ActiveRecord::Base
  def fixtures
    Fixtures.for_team_id(id)
  end
end

最后一個解決方案是我堅持使用的解決方案，因為它的作用域非常類似於只讀關聯，並防止了:finder_sql可能在以后發生的:finder_sql行為（我的意思是真的嗎？它如何知道如何合並更多條件嗎？有時它需要一個子查詢，一個子查詢嗎？

希望這可以幫助。

Answer 2

假設您有一個Team模型和一個Something模型，后者將具有home_team_id和away_team_id 。

class Something < ActiveRecord::Base
  belongs_to :home_team, :class_name => 'Team'
  belongs_to :away_team, :class_name => 'Team'

您將它們稱為something.away_team和something.home_team 。