Sample code doesn't work about dbh-pg HOT 3 CLOSED

var DBH = require('dbh-pg'),
    db = new DBH('postgres://postgres@localhost/db2test');

// var nodemailer = require('nodemailer'), // no included, used for this example only
//     transporter = nodemailer.createTransport(),
//     sendMail = Promise.promisify(transporter.sendMail);

var Promise = require('bluebird');

db.conn(this /* scope */) // fetch a connection in the pool
    .then(DBH.begin) // begin transaction
    .then(DBH.fetchAll('SELECT u.email, u.amount FROM users u where u.amount > $1', [1000]))
    .then(function(users) {

        // create a prepared statement
        var prepared = DBH.prepare('UPDATE users SET amount = 1000 where email = $email');

        // create a array of promises
        var emailPromises = users.map(function(user) {
            // single promise: exec the prepared statement and then send the email
            return this.exec(prepared(user))
                .then(function() {
//                     sendMail({
//                         from : '[email protected]',
//                         to : user.email,
//                         subject : ':p',
//                         text : 'You had $ '
//                             + user.amount
//                             + ' in your account. Sorry.'
//                     })
                });
        }.bind(this));

        return Promise.all(emailPromises);

    })
    .then(DBH.commit)
    .done(function () {
        this.done();
    }, function () {
        this.rollback()
            .then(DBH.done); // release the connection to the pool
    });