Question

So I have a Results table for a Tournament where multiple matches might occur with the same player.

So some sample data might be:

Results

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..

I want to prepare a scope that will count the Win fields that are set to True for each Player and and group by that count field.

So pseudo-code would be something like…

scope :most_wins, :all, :order_by => “Count(Player Wins)”

Is this even possible or should I re-think my database structure?

Answer 1

First and foremost: Named Scopes Are Dead

I suggest you do the following:

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")

In case you want it to be in Results table:

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

this gonna work but I find it a little bit ugly.

And if you want conditional count in the nested query the simple way would be:

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")

!!! Please note that it is prone to SQL injections if conditions argument is going to be directly built of user input.