轨道3 - 如何从模型中的行号与订单 [英] Rails 3 - How to get the row number from a model with an order by

问题描述

我组建了一个小的应用程序，在它排行榜的概念。基本上，该模型仅仅是一个player_name和current_score

I am putting together a small app that has a leaderboard concept in it. Basically, the model is just a player_name and a current_score.

我想要做的就是一个特定玩家的排名，并给予新的分数进来的时候，它需要是动态的。很显然，我也只是做一个正常的找到order by子句，然后我将不得不通过每个记录的循环。不是很有效的时候，我可以10万个的行。

what I want to do is get the ranking of a specific player, and given that new scores are coming in all the time, it needs to be dynamic. Obviously I could just do a normal find with an order by clause and then I would have to loop through each record. Not very efficient when I could have 100,000's of rows.

这是我应该采取什么样的做法有什么建议？

Any suggestions on what approach I should be taking?

下面是表迁移：

class CreateScores < ActiveRecord::Migration
  def self.up
    create_table :scores do |t|
      t.string  :player_name
      t.integer :current_score

      t.timestamps
    end
  end

  def self.down
    drop_table :scores
  end
end

编辑 举个例子，我有以下几点：

EDIT As an example, so I have the following:

Score.select('player_name, current_score').limit(20)
=> [#<Score player_name: "Keith Hughes", current_score: 9>, #<Score player_name: "Diane Chapman", current_score: 8>, #<Score player_name: "Helen Dixon", current_score: 4>, #<Score player_name: "Donald Lynch", current_score: 9>, #<Score player_name: "Shawn Snyder", current_score: 2>, #<Score player_name: "Nancy Palmer", current_score: 9>, #<Score player_name: "Janet Arnold", current_score: 1>, #<Score player_name: "Sharon Torres", current_score: 9>, #<Score player_name: "Keith Ortiz", current_score: 5>, #<Score player_name: "Judith Day", current_score: 3>, #<Score player_name: "Gregory Watson", current_score: 7>, #<Score player_name: "Jeremy Welch", current_score: 3>, #<Score player_name: "Sharon Oliver", current_score: 7>, #<Score player_name: "Donald Lewis", current_score: 7>, #<Score player_name: "Timothy Frazier", current_score: 7>, #<Score player_name: "John Richards", current_score: 1>, #<Score player_name: "Carolyn White", current_score: 4>, #<Score player_name: "Ronald Smith", current_score: 2>, #<Score player_name: "Emily Freeman", current_score: 9>, #<Score player_name: "Gregory Wright", current_score: 2>]

我怎样才能制定出唐纳德·刘易斯的排名？

How can I work out the ranking of "Donald Lewis" ?

推荐答案

您可以指望的具有更高current_score记录数。您仍然需要每条记录做（或做一个子查询您的SQL）。

You could count the number of records that have a higher current_score. You will still have to do it per record (or do a sub-query in your sql).

class Score < ActiveRecord::Base

  def ranking
    Score.count(:conditions => ['current_score > ?', self.current_score])
  end

end

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