Node.js Mongodb native-drive organisation

How to organise the Mongodb native-driver in a big project?

At the moment I use this code in every "model" which is basically just an object in a module.

users.js

var mongo = require('mongodb');

var Users = {};

Users.db = new mongo.Db(...);

Users.db.open = function(e, c){
  if(e){ throw new Error(e); } else {
  console.log('connection opened'); }
};

Users.c = Users.db.collection('users');

Users.login = function(username, rawPassword, callback){
  Users.c.findOne({ username: username }, function(e, o){
    if(o.password === encrypt(rawPassword)){ callback(o); }
    else { callback(null); }
  });
};

But would this be the best way to open a database connection in each separated model? How to do proper sharing of the connection between the models? Would this be a good solution:

database-connections.js

var mongo = require('mongodb');
var RedisClient = require('redis-client');

module.exports = {
 main: new mongo.Db(...),
 log: new mongo.Db(...),
 cache: new RedisClient(...)
};

so each time we use a database connection we can use this instead:

users.js

var mainDb = require('database-connections.js').main;
var logDb = require('database-connections.js').log;
var cacheDb = require('database-connections.js').cache;

mainDb.open(function(e, c)){
  if(e){ throw new Error(e); } else {
    mainDb.collection('users', function(e, c){
      // do work.
    });
  }
});