Node.js sequential mysql queries promise not resolving - mysql

Question

A route in app.js calls a function register(user) in a MySQL model, model.js. This register() calls displayNameTaken(display_name) which will return null if display name is available otherwise it will return a json object.
The promise in the app.post containing model.register(req.body) does not resolve.
If display name is taken register() will pass this json object back to the calling route.
If display name is not taken register() will register user and return back another json object back to the calling route.
The app never resolves the returned promise, app#113.
Or do you have any suggestions to what I should do instead?
Can you see what I have done wrong?
Output below:
1. When display name taken
app#113 [ undefined ]
model#73 { code: 12, message: 'e' }
2. Display name not taken, registration successful
app#113 [ undefined ]
model#73 undefined
model#61 110 //<- last insert id
The app never resolves the returned promise, app#113.
Or do you have any suggestions to what I should do instead?
Can you see what I have done wrong?
app.post('/api/register', function (req, res) {
Promise.all([
model.register(req.body)
]).then((r => {
console.log('app#113',r);// r=> undefined
res.status(200).json(r);
})).catch((e => {console.log(e);
res.status(500).json(e);
}));
});
function Model(db){
this.db = db;
}
//Function returns null if display name is not taken
Model.prototype.displayNameTaken = function(display_name){
return new Promise((resolve, reject, next) => {
var sql = "SELECT id FROM `users` WHERE `display_name` = ?";
var rv;
this.db.query(sql, [[display_name]], (err, result) => {
if (err) {
return resolve(err);
}
if(0 < result.length && result[0].id != undefined && result[0].id != NaN && 0 < result[0].id){
rv = {code: 12, message:'e'};
}else{
rv = null;
}
return resolve(rv);
});
});//Promise
}
model.register = function register(params){
if(params == undefined){
return;
}
var rv;
Promise.all([
this.displayNameTaken(params.display_name.trim())
]).then((r => {
return new Promise((resolve, reject, next) => {
if(r[0] == null){//display_name available
var sql = "INSERT INTO `users` (`display_name`, `email`, `hash`, `created`,`md51`, `md52`, `language`) VALUES ?";
var md51 = md5(randomString({length:32}));
var md52 = md5(randomString({length:32}));
var user = [[
params.display_name.trim(),
params.email.trim(),
passwordHash.generate(params.hash.trim()),
datetime.create().format('Y-m-d H:M:S'),
md51,
md52,
params.language
]];
this.db.query(sql, [user], function (err, result) {
if (err) {
return reject(err);
}
console.log('model#61',result.insertId);
if(0 < result.insertId){
rv = {code: 8, message:'i', md51: md51, md52: md52};
}else{
rv = {code: 0, message:'e'};
}
return resolve(rv);
});
}else{//display_name taken
rv = r[0];
}
console.log('model#73',rv);
return resolve(rv);
});//Promise
})).catch((e => {
console.log(e);
}));