Order Players on the SUM of their association model

问题

I have a database with 6500 players and each player has an average of 15 game results.

Use case

I want to generate a list of players, ordered by the sum of their prize money (a field in the results table). I prefer this to be in some sort of scope, so I can also filter the list on the player's country, etc.

Performance

I have seen posts that mention a cache_counter field for performance. In my case I have thousands of result records (75.000+) so I don't want the calculations being done every time someone visits the generated listings.

Question

What is the best pattern to solve this? And how do I implement it?

Models

class Player < ActiveRecord::Base
  has_many :results
end

class Result < ActiveRecord::Base
  belongs_to :player
end

Schemas

  create_table "players", :force => true do |t|
    t.string   "name"
    t.string   "nationality"
  end

  create_table "results", :force => true do |t|
    t.integer  "player_id"
    t.date     "event_date"
    t.integer  "place"
    t.integer  "prize"
  end

Update

What I am trying to accomplish is getting to a point where I can use:

@players = Player.order_by_prize

and

@players = Player.filter_by_country('USA').order_by_prize('desc')

回答1:

You should be able to use something like this:

class Player
 scope :order_by_prize, joins(:results).select('name, sum(results.prize) as total_prize').order('total_prize desc')  

Refer rails api - active record querying for details.

来源：https://stackoverflow.com/questions/10526012/order-players-on-the-sum-of-their-association-model