what's the simplest and most effective way to get random records from a mongodb collection?

I'm trying to get a list of users from my user collection, but need to get 20 from 10k+ randomly. What's t开发者_JS百科he cleanest and most effective way?

I was thinking of updating users with {random: Math.random()} every minute and then sorting by random....

Is there a cleaner / more effective way of doing this?

It looks like your solution is pretty good : http://cookbook.mongodb.org/patterns/random-attribute/

You can get a list of element and just change the offset

User.all.offset(rand(User.count).limit(20)