Keep track of global counters in MongoDB.

gistfile1.txt

module Counters
  def self.next_sequence(name, increment = 1)
    # find and increment (or initialize) counter
    counter = collection.find(_id: name).modify({ '$inc' => { seq: increment } }, upsert: true, new: true)

    # return new counter value
    counter['seq']
  end

  private

  def self.collection
    Mongoid.default_session['counters']
  end
end