NodeJs Synchronous MYSQL Query and Foreach - mysql

Question

I have some mysql Query's in NodeJs that depends to a above result. Here is my code:
const sms = async function() {
await connection.query('select * from sms where sms.status_id = 2',
(err, rows) => {
if (err) throw err
rows.forEach(row => {
startdate = moment(row.statdate).format('YYYY-MM-DD HH:mm:ss');
enddate = moment(row.enddate).format('YYYY-MM-DD HH:mm:ss');
connection.query('select * from positions where sms_id = "'+row.id+'" and verified is null order by date asc',
(err, rows2) => {
if (err) throw err
rows2.forEach(row2 => {
connection.query('HERE IS A QUERY TO INSERT A REGISTER IN ANOTHER TABLE', data, (err,res) => {
if (err) throw err
console.log(`Inserted ${res.insertId}`);
})
})
}
);
})
}
)
The problem is, that way, I don't have the expected result in the middle query.
How can i do this synchronous?
I try to use Promises, but i don't understand how to do.

Answer 1

In most cases, you should avoid synchronous functions, especially if running server operations.
Rather, I'd recommend using mysql2 and it's promise wrapper.
Then you can do:
const mysql = require('mysql2/promise');
...
// use promise, then, catch
const sms = async function() {
return connection.query('select * from sms where sms.status_id = 2')
.then(([smss]) =>
smss.map(row => {
connection.query('select * from positions where sms_id = "'+row.id+'" and verified is null order by date asc')
.then(([positions]) => positions)) // unwrap array
)
.then(positions =>
positions.map(row => connection.query('...'))
)
.catch(e => {
// process errors
});
};
// or use awaits
const sms = async () => {
let [smss] = await connection.query('select * from sms where sms.status_id = 2');
let positions = await Promise.all(smss.map(row => {
...
});
};
Alternatively, you can use some better SQL queries to simplify the process. Like this:
select *
from sms
join positions on (positions.sms_id = sms.id)
where sms.status_id = 2
and positions.verified is null
order by positions.date