use mongoose with co

connect.js

var mongoose = require('mongoose');
var db;

var connect = module.exports = function () {
  mongoose.connect('mongodb://localhost/events');
  db = mongoose.connection;
  db.on('error', function(err) {
    console.error('Error', err);
  });
  db.once('open', function() {
    console.log('connected successfully!');
  });
};

main.js

var co = require('co');
var query = require('./query');

require('./connect')();

co(query.list)({}); // find all
co(query.fetchById)('541bbc16f9cf1264094a9524');

query.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var EventSchema = new Schema({
    name: String,
    _id: Schema.ObjectId
  });
var Event = mongoose.model('Event', EventSchema);

var thunkify = require('./thunkify-model');
var find = thunkify(Event, 'find');
var findById = thunkify(Event, 'findById');

exports.list = function *(conditions) {
  var docs = yield find(conditions);
  return docs;
};

exports.fetchById = function *(id) {
  return yield findById(id);
};

thunkify-model.js

var thunkify = require('thunkify');

module.exports = function (model, method) {
  if (!isMongooseModel(model)) throw new TypeError('Can only thunkify a mongoose model');
  if ('function' != typeof model[method]) throw new TypeError('No such method found on mongoose model: ' + method);
  return thunkify(model[method].bind(model));
};

function isMongooseModel(o) {
  return o && o.model && 'model' === o.model.name;
}