[英]Multi level associations in rails
我正在创建一个应用程序来跟踪整个赛季的足球队。 但我被困在数据库的设计上。 一个装置有一个主队和一个客队。 我创建了一个具有两个外键的夹具模型-home_team和away_team,但是我无法使关联正常工作。 有任何想法吗? 每个装置都属于一个联赛。
简单的答案是:
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
但这对您不利,因为Team.fixtures无法正常工作。
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
将为您提供两个集合…但是将它们汇总起来必须使用红宝石进行,这非常危险。
class Team < ActiveRecord::Base
def fixtures(*args)
home_fixtures.all(*args) + away_fixtures.all(*args)
end
end
这也有问题,排序和限制都将增加(嘿,双关语,谁知道?)。
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
这很丑陋,但可能会起作用。 finder_sql似乎可以完成所需的工作。
另一个选择是使用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
最后一个解决方案是我坚持使用的解决方案,因为它的作用域非常类似于只读关联,并防止了:finder_sql
可能在以后发生的:finder_sql
行为(我的意思是真的吗?它如何知道如何合并更多条件吗?有时它需要一个子查询,一个子查询吗?
希望这可以帮助。
假设您有一个Team
模型和一个Something
模型,后者将具有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'
您将它们称为something.away_team
和something.home_team
。
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