Rails 3 Scopes - Show Posts With Children Only

gistfile1.rb

# this gets the last five "bookings"

scope :recent, lambda {|quantity| limit(5).order('id DESC')}

# I want to only fetch bookings that are valid for purchase, i.e. they have "festival tickets" reserved for campers.

# how do I get the five latest "bookings" _that have camper tickets_?
# ref - http://stackoverflow.com/questions/8250451/rails3-scope-for-count-of-children-in-has-many-relationship

scope :with_children, joins(:campers).
    select('bookings.*').
    group('bookings.id').
    having('count(campers.name) > 0')

# So you can use
Booking.with_children.recent(5)

# Is there any tidier way to do the "has children" query scope than this?
# I'd like to do Booking.has_children(:campers).recent(5) for example

# Scopes are "obselete"
# according to http://www.elabs.se/blog/24-scopes-are-obsolete

# But does ActiveAdmin let you define Class.method_name? as a scope?