Rails 3 select random follower query efficiency

I have a method that selects 5 random users who are following a certain user, and adds them to an array.

Relationship.find_all_by_followee_id( user.id ).shuffle[0,4].each do |follower|
   follower = User.find(follower.user_id)
  开发者_如何学编程 array.push follower
end
return array

I'm wondering, is this an efficient way of accomplishing this? My main concern is with the find_all_by_followee_id call. This returns a list of all the relationships where the specified user is being followed (this could be in the 100,000s). And then I shuffle that entire list, and then I trim it to the first 5. Is there a more efficient way to do this?

You can try this:

Relationship.find_all_by_followee_id( user.id, :order => 'rand()', :limit => 5 ) do |follower|
   follower = User.find(follower.user_id)
   array.push follower
end
return array

Btw, this will work with MySql. If you are using PostgreSQL or anything else you may need to change the rand() with any valid random function that your DB supports.

Some minor changes to make it a little more clean:

return Relationship.find_all_by_followee_id( user.id, :order => 'rand()', :limit => 5 ).collect {|follower| User.find(follower.user_id) }

You can also use a join in there in order to prevent the 5 selects but it won't make much difference.

Edit1:

As @mike.surowiec mentioned.

"Just for everyones benefit, translating this to the non-deprecated active record query syntax looks like this:"

Relationship.where(:followee_id => user.id).order( "random()" ).limit( 5 ).collect {|follower| User.find(follower.user_id) }