Rails 3 Order Records By Grand-child Count

Question

I'm trying to do some fairly complicated record sorting that I was having a bit of trouble with. I have three models:

    class User < ActiveRecord::Base

    has_many :registers
    has_many :results, :through => :registers

    #Find all the Users that exist as registrants for a tournament
    scope :with_tournament_entrees, :include => :registers, :conditions => "registers.id IS NOT NULL"

end

Register

class Register < ActiveRecord::Base
  belongs_to :user
  has_many :results
end

Result

class Result < ActiveRecord::Base
  belongs_to :register 
end

Now on a Tournament result page I list all users by their total wins (wins is calculated through the results table). First thing first I find all users who have entered a tournament with the query:

User.with_tournament_entrees

With this I can simply loop through the returned users and query each individual record with the following to retrieve each users "Total Wins":

user.results.where("win = true").count()

However I would also like to take this a step further and order all of the users by their "Total Wins", and this is the best I could come up with:

User.with_tournament_entrees.select('SELECT *, 
                                    (SELECT count(*)  
                                     FROM results 
                                     INNER JOIN "registers" 
                                     ON "results"."register_id" = "registers"."id" 
                                     WHERE "registers"."user_id" = "users.id" 
                                     AND (win = true)
                                    ) AS total_wins 
                                     FROM users ORDER BY total_wins DESC')

I think it's close, but it doesn't actually order by the total_wins in descending order as I instruct it to. I'm using a PostgreSQL database.

Edit:

There's actually three selects taking place, the first occurs on User.with_tournament_entries which just performs a quick filter on the User table. If I ignore that and try

SELECT *, (SELECT count(*) FROM results INNER JOIN "registers" ON "results"."register_id" = "registers"."id" WHERE "registers"."user_id" = "users.id" AND (win = true)) AS total_wins FROM users ORDER BY total_wins DESC; 

it fails in both PSQL and the ERB console. I get the error message:

PGError: ERROR: column "users.id" does not exist

I think this happens because the inner-select occurs before the outer-select so it doesn't have access to the user id before hand. Not sure how to give it access to all user ids before than inner select occurs but this isn't an issue when I do User.with_tournament_entires followed by the query.

Answer 1

In your SQL, "users.id" is quoted wrong -- it's telling Postgres to look for a column named, literally, "users.id".

It should be "users"."id", or, just users.id (you only need to quote it if you have a table/column name that conflicts with a postgres keyword, or have punctuation or something else unusual).