ActiveRecord and SELECT AS SQL statements

Question

Hi all,

I am developing in Rails an app where I would like to rank a list of users based on their current points. The table looks like this: user_id:string, points:integer. Since I can't figure out how to do this "The Rails Way", I've written the following SQL code:

self.find_by_sql ['SELECT t1.user_id, t1.points, COUNT(t2.points) as user_rank FROM registrations as t1, registrations as t2 WHERE t1.points <= t2.points OR (t1.points = t2.points AND t1.user_id = t2.user_id) GROUP BY t1.user_id, t1.points ORDER BY t1.points DESC, t1.user_id DESC']

The thing is this: the only way to access the aliased column "user_rank" is by doing ranking[0].user_rank, which brinks me lots of headaches if I wanted to easily display the resulting table.

Is there a better option?

Answer 1

Try adding user_rank to your model.

class User < ActiveRecord::Base

  def rank
   #determine rank based on self.points (switch statement returning a rank name?)
  end

end

Then you can access it with @user.rank.

Answer 2

What if you did:

SELECT t1.user_id, COUNT(t1.points) 
FROM registrations t1 
GROUP BY t1.user_id 
ORDER BY COUNT(t1.points) DESC

If you want to get all rails-y, then do

cool_users = self.find_by_sql ['(sql above)']

cool_users.each do |cool_user|
  puts "#{cool_user[0]} scores #{cool_user[1]}"
end

Answer 3

how about:

@ranked_users = User.all :order => 'users.points'

then in your view you can say

<% @ranked_users.each_with_index do |user, index| %>
  <%= "User ##{index}, #{user.name} with #{user.points} points %>
<% end %>

if for some reason you need to keep that numeric index in the database, you'll need to add an after_save callback to update the full list of users whenever the # of points anyone has changes. You might look into using the acts_as_list plugin to help out with that, or that might be total overkill.