Mongoid random document

Question

Lets say I have a Collection of users. Is there a way of using mongoid to find n random users in the collection where it does not return the same user twice? For now lets say

Answer 1

The best solution is going to depend on the expected size of the collection.

For tiny collections, just get all of them and .shuffle.slice!

For small sizes of n, you can get away with something like this:

result = (0..User.count-1).sort_by{rand}.slice(0, n).collect! do |i| User.skip(i).first end

For large sizes of n, I would recommend creating a "random" column to sort by. See here for details: http://cookbook.mongodb.org/patterns/random-attribute/ https://github.com/mongodb/cookbook/blob/master/content/patterns/random-attribute.txt