Select n objects randomly with condition in Rails

I have a model called Post, with a column called vote, and it has a big number of posts

I want to select n posts randomly开发者_如何学运维 that have >=x votes. n is very small compared to the number of posts

What is the best way to do this? I've tried a couple of ways that seem to be very inefficient. Thanks

If you're on MySQL, you could order all the posts that meet the greater than criteria randomly and select the top n.

The actual query would look like

SELECT * FROM posts WHERE votes >= x ORDER BY rand() LIMIT n

Haven't tested this, but something like this should work in Rails:

Post.all(:conditions => ["votes >= ?", x], :order => "rand()", :limit => n)