ruby-on-rails-3 - Rails 3 按自累积计数对范围进行排序

Question

所以我有一个锦标赛的结果表，其中同一玩家可能会发生多场比赛。

所以一些示例数据可能是:

结果

Player_ID | Match_ID|Win|Elapsed_Time|etc..
1         |    1    |T  | 1:00       |etc..
2         |    1    |F  | 1:00       |etc..
1         |    2    |T  | 3:00       |etc..
3         |    2    |F  | 3:00       |etc..

我想准备一个范围，对每个玩家设置为 True 的 Win 字段进行计数，并按该计数字段进行分组。

所以伪代码会是这样的......

scope :most_wins, :all, :order_by => “计数(玩家获胜)”

这是否可能，或者我应该重新考虑我的数据库结构？

Answer 1

首先也是最重要的:Named Scopes Are Dead

我建议您执行以下操作:

class Players < ActiveRecord::Base
  ....
  def self.with_win_count
    #inner join if you want to filter out those who doesn't have any match, otherwise is should be left outer 
    joins("inner join (select Player_ID, count(Match_ID) as win_count from Results where Win = true group by Player_ID) t on (t.Player_ID = Player.ID)")
  end
end

#somewhere in controller you would do
best_players = Player.with_win_count.where("win_count > ?", [10]).order("win_count DESC")

如果您希望它出现在结果表中:

class Results < ActiveRecord::Base
  ....
  def self.with_win_count
    joins("inner join (select Player_ID, count(Match_ID) as win_count from Results where Win = true group by Player_ID) t on (t.Player_ID = Results.Player_ID)")
  end
end

这会起作用，但我发现它有点难看。

如果您想在嵌套查询中进行条件计数，简单的方法是:

class Players < ActiveRecord::Base
  ....
  def self.with_match_count(conditions)
    #inner join if you want to filter out those who doesn't have any match, otherwise is should be left outer 
    joins("inner join (select Player_ID, count(Match_ID) as match_count from Results where #{conditions} group by Player_ID) t on (t.Player_ID = Player.ID)")
  end
end
some_players = Player.with_match_count("Win = true").where("match_count > ?", [10]).order("match_count DESC")

!!! 请注意，如果 conditions 参数直接由用户输入构建，则很容易发生 SQL 注入(inject)。