Array push doesn't work in promise node.js - mysql

Question

I have previously attempted to wrap this code in callbacks, async what ever the language has to offer. However, I am still getting nowhere.
The problem is, that members remains empty, even though it should be pushed with info.
channels however, works fine.
Weirdly, the
console.log(values);
prints before the
console.log(result);
Interestingly though,
console.log(result)
does have the correct data, but where I do
console.log(members)
it is empty.
I have tested, the query is all correct, it is literally a problem with the pushing and getting the result earlier than it currently is returned (I assumed Promises would mean things would be more in order, but maybe my understanding is wrong).
Here is the full code:
module.exports.controller = (query, helper, cache, Database, mysql, config) => {
return async (req, res) => {
let zone = req.body.zone;
let returning = {};
if(!zone){
return res.json(helper.responseJson(false, 'Missing parameter "zone"'));
}
function teleport_available(channel_name){
if(channel_name.indexOf("Nadaj / Usuń") === -1){
return true;
}else{
return false;
}
}
await mysql.query("SELECT * FROM flamespeak_pbot.zones WHERE zone = '"+ zone +"'", async (err, row) => {
if (err) throw err;
row = row[0];
if (row.length == 0) {
return res.json(helper.responseJson(false, "Zone not found."));
} else {
var channelsPromise = new Promise((resolve, reject) => {
const channels = [];
JSON.parse(row.assignGroupAdditional_ch).forEach(additionalCh => {
cache.channelList.filter(channel => channel.cid == additionalCh).forEach(mainCh => {
mainCh.propcache.teleport_available = teleport_available(mainCh.propcache.channel_name);
mainCh.propcache.subchannels = [];
cache.channelList.filter(channel => channel.pid == additionalCh).forEach(subCh => {
subCh.propcache.teleport_available = teleport_available(mainCh.propcache.channel_name);
mainCh.propcache.subchannels.push(subCh);
});
channels.push(mainCh.propcache);
});
});
resolve(channels);
});
var membersPromise = new Promise((resolve, reject) => {
let members = [];
query.serverGroupClientList(row.serverGroupID)
.then(serverGroupList => {
serverGroupList.forEach(member => {
var sql = "SELECT * FROM teamspeak_clientDbList WHERE client_database_id = '" + member.cldbid + "'";
mysql.query(sql, function (err, result) {
if (err) throw err;
console.log(result);
members.push(result);
})
});
})
.then(() => {
console.log(members);
resolve(members);
});
});
}
Promise.all([channelsPromise, membersPromise]).then(function(values) {
console.log(values);
returning = {
'channels' : values[0],
'members' : values[1],
'pbot' : row,
};
res.send(helper.responseJson(true, returning));
});
});
};
};

Answer 1

With respect, your mixture of callbacks, promises, and async / await is very hard to follow. You'd be wise to simplify it. (Or risk having your name cursed by the person who must maintain this code later.)
The callback in your second mysql.query() method is called whenever MySQL wants (whenever the query finishes or fails). But you don't resolve any promise or return from an async method within that callback's code. So, your console.log(result) shows a correct result, but your other code doesn't get access to that result; your Promise.all resolves before that method is called.
Something like this would, in general, be the right thing to do:
var sql =
"SELECT * FROM teamspeak_clientDbList WHERE client_database_id = '" +
member.cldbid + "'";
mysql.query(sql, function (err, result) {
if (err) throw err;
console.log(result);
members.push(result);
resolve (result); // <<< add this line
})
But in your case it probably won't work: your function query.serverGroupClientList() seems to return a Promise. You didn't show us that function, so it's hard to guess how to weave that into your logic.

Answer 2

query.serverGroupClientList(row.serverGroupID)
.then(serverGroupList => {
let members = [];
serverGroupList.forEach(member => {
var sql = "SELECT * FROM teamspeak_clientDbList WHERE client_database_id = '" + member.cldbid + "'";
mysql.query(sql, function (err, result) {
if (err) throw err;
console.log(result);
members.push(result);
})
});
resolve(members);
})
Try this

Answer 3

SELECT * FROM teamspeak_clientDbList
While iterating serverGroupList, the db Query on each element is asynchronous. Hence empty members.
Moreover foreach expects a synchronous function so you will have to use for-loop or for-of to use async-await feature.
var membersPromise = new Promise((resolve, reject) => {
let members = [];
query.serverGroupClientList(row.serverGroupID)
.then(async (serverGroupList) => {
console.log("serverGroupList: ", serverGroupList);
for (let index = 0, arrLen = serverGroupList.length; index < arrLen; index++) {
let member = serverGroupList[index];
var sql = "SELECT * FROM teamspeak_clientDbList WHERE client_database_id = '" + member.cldbid + "'";
await mysql.query(sql, async function (err, result) {
if (err) throw err;
console.log(result);
members.push(result);
});
}
console.log(members);
resolve(members);
});
});
Nested Code can be improved if you write a wrapper function for db queries which returns a promise.
function fireQuery(mysql, query, params = []) {
return new Promise((resolve, reject) => {
return mysql.query(query, params, (err, data) => {
if (err) return reject(err);
return resolve(data);
});
});
}
// ex -1
let rows = await fireQuery(mysql,query,params);
if(rows.length == 0) {} // your code
// ex-2
let member = await fireQuery(mysql,query2,params2);
members.push(member);