PriorityOrderScopes

create_table "jobs" do |t|
  t.string "name"
  t.datetime "started_at"
end

class Job < ActiveRecord::Base
  include PriorityOrderScopes
  
  priority_order_scopes "started_at"
end

Job.priority_order # => Job.order("started_at")

# by default, next and previous use the priority order (unless there
# is a default_scope with an order defined)

Job.next(Job.priority_order.first) # => the job that starts second
Job.previous(Job.priority_order.first) # => nil
Job.previous(second_job) # => Job.priority_order.first

# next and previous class methods respect the current scope

Job.order('name').next(Job.first) # => the job with the next name

# next and previous instance methods always use priority order

job = Job.priority_order.first
job.next # => the job that starts second

job = Job.order('name').first
job.previous # => the job that starts before the first job in alpha order