Fetch random GORM model

Despite busy schedule at work and a year old daughter at home, who now requires constant attention, I was able to get some time to work on the Grails community site (Grails Crowd).

As a part of it, I wanted to have a feature to display a 'random' user (a 'member') In fact, keep displaying a random user as long as 'Discover users' link is being clicked. You know, kind of like Flickr's "Explore" feature. So with a help of standard JDK library features i.e. 'java.utils.Collections.shuffle()' and Groovy closures, here's what I've come up with:

MemberController's action:

...

def findRandom = {
        def member = null

        withMemberIds { memberIds ->
            //Pick the last one
            member = Member.get(memberIds[-1])
            //Then remove it from the list
            memberIds.pop()
        }

        if(member) {
            render(view: 'discover', model: [member: member])
        }
        else {
            //No one is registered yet - just 'go home'
            redirect(uri:'/')
        }
    }

    private def withMemberIds(closure) {
        def memberIds = session.memberIds
        if (!memberIds) {
            memberIds = Member.withCriteria {
                projections {
                    property('id')
                }
            }
            if (!memberIds.isEmpty()) {
                //Some members are in the database:
                //Shuffle 'em up
                Collections.shuffle(memberIds)
                session.memberIds = memberIds
            }
            else {
                //No members are in the database
                return
            }
        }
        closure(memberIds)
        if (memberIds.isEmpty()) {
            session.memberIds == null
        }
    }

...

It works like a charm.

Later...