How do I keep the last 10 entries and delete the rest?

User has more than 20 records in a table. I only want to keep开发者_如何学Python the last 10 entries. Which means I want to delete the rest.

I want to do this for each user in that table as well.

How should I go about this?

Item.destroy(Item.order('created_at').all.last(10).map(&:id))

There's probably a less expensive way to do it, but that should work for you.