acl9_query_by_role.rb

# If you know of a better way to do this, please fork the gist!

def query_by_role(object, role_name)
  corresponding_role_ids = object.accepted_roles.all(:conditions => { :name => role_name }).map(&:id)

  # this will now return all users that have +role_name+ on +object+
  User.all(:include => :roles, :conditions => ['roles.id IN (?)', corresponding_role_ids])
end