Multiple Promises and/or Async Functions

I’m greeting everyone,

after learning more about NodeJS and mysql, i run into synchronizing problems. I want to avoid using async&await and to rarely use try&catch instead keep on .then() and .catch(), but I having my issues with multiple _async_ functions (sql queries), especially if they are called inside another .then() because I need to loop through sql results. The return of getPlayerSubjects() is executed before its arrays/objects are filled with subqueries. How to synchronize it, so that the .then() after getPlayerData() can use the db data? Maybe I’m too new to Promises and asynchronous functions.

Here is the relevant code:

“`
const playersData = {};
const subjectFactors = {};
const dbpool = mysql.createPool({…, multipleStatements:true});

function query(sql) {
return new Promise((resolve, reject) =>{
try {
dbpool.query(sql, (err, result) => {
if (err){
return reject(err)
}

return resolve(result)
});
}
catch(event) {
reject(event)
}
})
}

function getPlayerSubjects(request, subjectResults) {
const playerSubjects = {};

for(const subjectResult of subjectResults) { // for all units
if(subjectResult.boolval) { // simple boolean evaluation
query(‘SELECT * FROM ranks WHERE rank_id=’+subjectResult.start+’;’
+’ SELECT * FROM ranks WHERE rank_id=’+subjectResult.end)
.then((startEndResults) => { // when both sqls done
if(breaksThreshold(playerRank, (startEndResults[1][0].position-startEndResults[0][0].position)*subjectResult.part) { // simple function evaluation
subjectResult[‘subject_subs’] = [];
playerSubjects[subjectResult[‘subject_id’]] = query(‘SELECT * WHERE subsubject_subject_id=’+subjectResult[‘subject_id’])
.then((subsubjectResults) => {
for(const subsubjectResult of subsubjectResults) {
updateFactorsOfPlayer(subjectResult[‘subject_player_id’], subsubjectResult[‘subsubject_subject_id’],);
subjectResult[‘subject_subs’].push(subsubjectResult);
}
});
playerSubjects[subjectResult[‘subject_id’]] = subjectResult;
}
});
}
}

return {subjects:playerSubjects, subjectFactors:subjectFactors};

function getPlayerData(request, playerResults) {
return {friends:getPlayerFriends(request, playerResults[0]), …getPlayerSubjects(request, playerResults[1])}; // build event data structure
}

function sendPlayerEvent(request, response) {
query(‘SELECT * FROM ranks’
+’; SELECT * FROM subjects’)
.then((playerResults) => {
getPlayerData(request, playerResults)
.then((currentPlayerData) => {
if(notEqual(playersData[request.query.id], currentPlayerData)) { // data has changed
playersData[request.query.id] = currentPlayerData; // set new player data
response.write(`data: ${JSON.stringify({player:playersData[request.query.id]})}nn`);
}
});
})
.catch((error) => {
console.error(error);
});
}
“`