Bringing separate asynchronous branches back into one branch again - mysql

Question

I am working on a node js app which makes use of the express and mysql libraries.
I have a MySQL user table with the following columns:
auto incrementing primary id
username varchar unique
There is no password, etc.
Other tables include:
room
id
room_name
user_room
id
user_id (FK to user table)
room_id (FK to room table)
details
id
user_room_id (FK to user_room table)
col1
col2
col3
Upon trying to connect to a room, I want the database to try pulling their data for that room.
If the data does not exist, I want to see if the username exists in the user table.
If the username does exist, I want to get their id.
If the username does not exist, I want to add their name to the user table and capture the last inserted id
Once having their id, I want to add a record to the user_room table for that user and then several records to the details table based on the newly inserted id in the user_room table.
I seem to be getting into a tangled web going into so many layers.
This is what my code currently looks like:
socket.on('enter room', function(data, callback){
var sql = "select col1, col2, col3 from room JOIN user_room on room.id = user_room.room_id JOIN user on user_room.user_id = user.id JOIN details on user_room.id = details.user_room_id where username = ?";
db_connection.query(sql, [socket.nickname], function (err, result) {
if (err){
console.log("ENTER ROOM DB ERROR: " + err);
return;
}
if (!result.length){
var sql = "select id from user where name = ?";
db_connection.query(sql, [socket.nickname], function (err, result){
if (err){
console.log("ENTER ROOM, SELECT ID DB ERROR: " + err);
return;
}
if (!result.length){
var sql = "insert into user (name) values (?)";
db_connection.query(sql, [socket.nickname], function(err, result){
if (err){
console.log("ENTER ROOM, INSERT ID DB ERROR: " + err);
return;
}
id = result.insertId;
});
}
else {
id = result[0].id;
}
});
//We need to pull things back into one branch again here
//Using the user id and room id I will insert a record into the user_room table
//Then using the newly inserted id in the user_room table, I need to add records to a details table
}
});
//Send col1, col2, and col3 data back to user
//This section here also needs to be pulled back into one branch again
io.sockets.emit('details', result);
});
It mostly works, but because I branch off in two different ways to get the user id (one if it already exists, and one if I need to insert it), I do not know how to pull it back together again into one branch.
What can I do to pull my code back into one branch again so that I can use the id again? Or, is there a better way of approaching this altogether?
A side question: Can I safely remove the "callback" in my opening function, or should I be using this somewhere in my code? I feel that the emit is like a callback to the client so that I do not need "callback" here.

Answer 1

I took a different approach to get userId on upsert. I used promise to send the room data immediately, if available.
socket.on('enter room', function (data, callback) {
let nickName = '';
let roomId = '';
return bookingDetails(nickName).then((details) => {
if (details.length !== 0) {
return Promise.resolve(details);
} else {
return createRoom(nickName, roomId);
}
}).then((details) => {
io.sockets.emit('details', details);
});
});
function createRoom(nickName, roomId) {
return getUserDetails(nickName).then((userId) => {
return insertUserRoom(userId, roomId); //your function
}).then((userRoomDetails) => {
return insertDetails(userRoomDetails); //your function
});
}
function bookingDetails(nickName) {
let sql = "select col1, col2, col3 from room " +
"JOIN user_room on room.id = user_room.room_id " +
"JOIN user on user_room.user_id = user.id " +
"JOIN details on user_room.id = details.user_room_id where username = ?";
return new Promise((resolve, reject) => {
db_connection.query(sql, [nickName], function (err, details) {
if (err) {
return reject("ENTER ROOM DB ERROR: ");
}
return resolve(details);
});
});
}
function getUserDetails(nickName) {
return new Promise((resolve, reject) => {
let sql = "select id from user where name = ?";
db_connection.query(sql, [nickName], function (err, userDetail) {
if (err) {
return reject(err);
}
if (userDetail === null) { //insert
return createUser(nickName);
}
return userDetail;
}).then((userDetail) => {
return resolve(userDetail.id);
});
});
}
function createUser(nickName) {
return new Promise((resolve, reject) => {
let sql = "insert into user (name) values (?)";
db_connection.query(sql, [nickName], function (err, userDetail) {
if (err) {
return reject(err);
}
return resolve(userDetail);
});
});
}