Mine

config_file = "#{Rails.root}/config/mongodb.local.yml"
config_file.gsub!(/\.local/, "") if !File.exist?(config_file)
db_config = YAML::load(File.read(config_file))

if db_config[Rails.env] && db_config[Rails.env]['adapter'] == 'mongodb'
  mongo  = db_config[Rails.env]
  logger = ENV['LOG_MONGO'] ? Rails.logger : nil 
  if ENV['REPLICA_SET_NAME']
    MongoMapper.connection = Mongo::ReplSetConnection.new(*ENV['REPLICA_HOSTS', :read_secondary => true, :logger => logger, :rs_name => ENV['REPLICA_SET_NAME']
  else
    mongo['hostname'] = ENV['MONGODB_HOST'] if ENV['MONGODB_HOST']
    MongoMapper.connection = Mongo::Connection.new(mongo['hostname'], 27017, :logger => logger)
  end 

  MongoMapper.database  = mongo['database']
end

  Delayed::Worker.backend = :mongo_mapper
require 'lib/bson_ordered_hash'