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ViewsWhy is this async function returning empty on the first try, but then it returns everything?
I'm trying to insert data to my db, and the query is inside a map loop, so i'm using an async function to wait for the loop to end, and store all the results in my variable "practicasAgregadas".
This is how i call the function:
insertarPracticas(turno_id, req.body.lista_codigos_practicas, queryInsertarPracticas)
.then(result => {
res.status(200).json({
"Practicas Agregadas": result
})
})
This is the function:
async function insertarPracticas(turno_id, req, queryInsertarPracticas) {
const res = await Promise.all(req.map(r => {
connection.query(
queryInsertarPracticas, [turno_id, r], (error2, row2) => {
if (error2) {
console.log("Error al insertar turno detalle (prácticas): " + r + " " + error2);
practicasNoAgregadas += r + "-";
} else {
console.log("Turnos detalle agregados " + r);
practicasAgregadas += r + "-";
console.log("practicas " + practicasAgregadas);
}
});
return practicasAgregadas;
})
)
console.log("en async " + res[0]);
return res;
}
On the first try, it returns empty:
This is the console:
And on the second try, it does return, but it repeats 3 times:
And the console:
1 answers
Answer question0
Most modern JS libs that use async functions will return a promise, but will often not return a promise if the callback is supplied.
So assuming connection.query does return a promise, then the code below should do what your after..
async function insertarPracticas(turno_id, req, queryInsertarPracticas) {
const res = await Promise.all(
req.map(async (r) => {
try {
const row2 = await connection.query(queryInsertarPracticas, [
turno_id, r
]);
console.log("Turnos detalle agregados " + r);
practicasAgregadas += r + "-";
console.log("practicas " + practicasAgregadas);
} catch (e) {
console.log(
"Error al insertar turno detalle (prácticas): " +
r + " " + error2
);
practicasNoAgregadas += r + "-";
}
return practicasAgregadas;
})
);
console.log("en async " + res[0]);
return res;
}
Remember, don't use a callback, or that could indicate to the lib that your not wanting a promise returning.
If for some reason the lib has not been updated for a long while, you will need to promisify the query..
In node, there is a nice utility called promisify https://nodejs.org/api/util.html#utilpromisifyoriginal that will make this bit easier.
eg.
const conQuery = util.promisify(connection.query);
const row2 = await conQuery(queryInsertarPracticas....
If the callback is not in the form (error, result) you would need to use a Promise constructor.. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/Promise , but looking at your code (error2, row2) => that shouldn't be required.