express app correct way to connect to mongo db?

I have the following directory layout that contains a node.js / express application:

server.coffee
server.js
src
├── config
│   └── index.coffee
├── controllers
│   ├── index.coffee
│   └── user.coffee
├── index.coffee
├── models
│   └── user
│       └── user.coffee
├── routes.coffee
└── utils
    ├── dbconnect.coffee
views
├── 404.blade
├── 500.blade
├── index.blade
└── user
    ├── create.blade

the /src/config/index.coffee has details of the mongo URL which is i then export as DB_URL

#### Config file
# Sets application config parameters depending on `env` name

logger = require "../utils/logger"
logCategory = "Server config"

DB_HOST = "localhost"
DB_PORT = "27017"
DB_NAME = "zmgc"
DB_URL = null
DB_USER = null
DB_PASS = null


# Connecting to dexies database on mongodb
boundServices = if process.env.VCAP_SERVICES then JSON.parse(process.env.VCAP_SERVICES) else null
unless boundServices
    if DB_USER and DB_PASS
        DB_URL = "mongodb://#{DB_USER}:#{DB_PASS}@#{DB_HOST}:#{DB_PORT}/#{DB_NAME}"
    else
        DB_URL = "mongodb://#{DB_HOST}:#{DB_PORT}/#{DB_NAME}"
else
    service_type = "mongodb-1.8"
    credentials = boundServices["mongodb-1.8"][0]["credentials"]
    DB_URL = "mongodb://" + credentials["username"] + ":" + credentials["password"] + "@" + credentials["hostname"] + ":" + credentials["port"] + "/" + credentials["db"]

#Set the current environment to true in the env object
exports.setEnvironment = (env) ->
  logger.info "Set app environment: #{env}", logCategory

  switch(env)
    when "development"
      exports.DEBUG_LOG = true
      exports.DEBUG_WARN = true
      exports.DEBUG_ERROR = true
      exports.DEBUG_CLIENT = true
      exports.DB_URL = DB_URL

    when "testing"
      exports.DEBUG_LOG = true
      exports.DEBUG_WARN = true
      exports.DEBUG_ERROR = true
      exports.DEBUG_CLIENT = true
      exports.DB_URL = DB_URL

    when "staging"
      exports.DEBUG_LOG = true
      exports.DEBUG_WARN = true
      exports.DEBUG_ERROR = true
      exports.DEBUG_CLIENT = true
      exports.DB_URL = DB_URL

    when "production"
      exports.DEBUG_LOG = false
      exports.DEBUG_WARN = false
      exports.DEBUG_ERROR = true
      exports.DEBUG_CLIENT = false
      exports.DB_URL = DB_URL
    else
      logger.info "Environment #{env} not found", logCategory

and then in /src/utils/dbconnect.coffee, i have the following:

# Connecting to database on mongodb
config = require "../config/index"
logger = require("./logger")
mongoose = require("mongoose")
mongoose.set "debug", true

logCategory = "DATABASE Connection"

db_connect_mongo = init: (callback) ->
  self = this
  mongo_options = db:
      safe: true
  db_url = config.DB_URL
  mongoose.connect db_url, mongo_options
  db = self.db_mongo = mongoose.connection

  db.on "error", (error) ->
    logger.error "ERROR connecting to: " + db_url, logCategory
    callback error, null

  db.on "connected", ->
    logger.info "SUCCESSFULLY connected to: " + db_url, logCategory
    callback true, db

  db.on "disconnected", ->
    logger.info "DISCONNECTED from the database: " + db_url, logCategory

# check and connect to Redis

exports = module.exports = db_connect_mongo

am i correct in assuming that once i start the application, /src/index.coffee :

express = require "express"
logger = require "./utils/logger"

# Initialize logger
logger.configure()

#### Application initialization
# Create app instance.
app = express()

# Define Port
app.port = process.env.PORT or process.env.VMC_APP_PORT or process.env.VCAP_APP_PORT or 3000

# Config module exports has `setEnvironment` function that sets app settings depending on environment.
config = require "./config"

logCategory = "Server"

app.configure "development", "testing", "staging", "production", ->
  config.setEnvironment app.settings.env

# Database connection
dbconnection = require "./utils/dbconnect"
dbconnection.init (result) ->
  if result
    logger.info "Database initialized", logCategory

the connection stays open, so that i don't have to keep opening and closing this?

is this the correct approach to do this?

any advice much appreciated.