Express: how to end response - node.js

Question

I new in Nodejs and faced some problems and need help
I broke down my app into modules and controllers
in app.js
app.use('/api/sync', syncDataRouter)
and in syncDataRouter.js
const routes = function (con, Reading, ReadingSummary) {
const syncDataRouter = express.Router();
const syncDataController = require('../controller/syncDataController')(con, Reading, ReadingSummary);
//Get All Readings from Database and push it to Mongo-db
syncDataRouter.route('/')
.get(syncDataController.sync);
return syncDataRouter;
};
module.exports = routes;
and in controller
const syncDataController = function (con, Reading, ReadingSummary) {
function getAllCompletedSessions() {
return new Promise((resolve, reject) => {
const sql = 'SELECT * FROM session WHERE endTime IS NOT NULL';
con.query(sql, (err, rows) => {
if (err) reject(new Error(err));
resolve(rows);
});
});
};
function getSessionPlayers(sessionId) {
return new Promise((resolve, reject) => {
const sql = 'SELECT * FROM sessionplayers WHERE sessionId = ?';
con.query(sql, [sessionId], (err, rows) => {
if (err) reject(new Error(err));
resolve(rows);
});
});
};
const sync = (req, res) => {
getAllCompletedSessions()
.then(sessions => {
})
.catch(err => {
res.status(500).send({ message: err.message });
});
//The Problem
res.json('Done');
};
return {
sync: sync
}
}
module.exports = syncDataController;
the problem is if any error happened enter a catch block and also continue until res.json('Done'); and sent a message can't set headers after they are sent how to handle a situation like that

Answer 1

Try making the sql queries async
const syncDataController = function (con, Reading, ReadingSummary) {
async function getAllCompletedSessions() {
return new Promise((resolve, reject) => {
const sql = 'SELECT * FROM session WHERE endTime IS NOT NULL';
await con.query(sql, (err, rows) => {
if (err) reject(new Error(err));
resolve(rows);
});
});
};
async function getSessionPlayers(sessionId) {
return new Promise((resolve, reject) => {
const sql = 'SELECT * FROM sessionplayers WHERE sessionId = ?';
await con.query(sql, [sessionId], (err, rows) => {
if (err) reject(new Error(err));
resolve(rows);
});
});
};
const sync = (req, res) => {
getAllCompletedSessions()
.then(sessions => {
})
.catch(err => {
res.status(500).send({ message: err.message });
});
//The Problem
res.json('Done');
};
return {
sync: sync
}
}
module.exports = syncDataController;