model.rb

# Since Mongoid switched to its own driver, many of the mongo API
# (available in mongo-ruby-drive) are missing. This is allows you
# to rename a collection thru command message.
#
# Be aware that the API constantly changes in mongoid
#
# Mongoid (3.1.0), Moped (1.4.2)

class MyModel
  include Mongoid::Document

  def self.rename(to, dropTarget = false)
    database = collection.database
    database.session.with(:database => "admin", :consistency => :strong) do |session|
      session.command({ :renameCollection => "#{database.name}.#{collection_name}", :to => "#{database.name}.#{to}", :dropTarget => dropTarget })
    end
  end
end