NODEJS Getting data from database , then use them

Question

i want to get data from database and array-loop That's my actual structure. I have already test a tons of things without success

app.get('/url' async (req,res)=> {
    value = []
    async function myFunction(){
    
        myArray.map(async(data)=> {
            db('MY QUERY')
            .then((res)=> {
                value.push(res)
            })
        })
    }
    await myFunction()
    console.log(value) // Always empty
})

I'm open to any tips from you ! :)

EDIT : More information about database connection: myArray is like : ["a","*","b","myOwnMathFunction(a)"] but not important here Query : "SELECT * FROM User WHERE id='1' " //Verified & work

const bd = mysql.createConnection({ MY CONFIG})
    const db =  util.promisify(bdd.query).bind(bdd)

Please refer to this stackoverflow.com/questions/40140149/… — Akash Jp
– Akash Jp, Commented May 21, 2021 at 10:19
What is your SQL query? And provide some more code related to database connection and all. — zx01
– zx01, Commented May 21, 2021 at 11:07
@zx01 My SQL query work & my database connection work too , i only have problem with async notion. I added more informations on the post — Jogoldirus
– Jogoldirus, Commented May 21, 2021 at 11:18
Yeah I understand but you need to give some context like what is myArray here? — zx01
– zx01, Commented May 21, 2021 at 11:21
@zx01 that's an array of math operator & maded functions used in my loop — Jogoldirus
– Jogoldirus, Commented May 21, 2021 at 11:31

Tomalak · Accepted Answer · 2021-05-21 11:31:37Z

1

Use Array#map() to create multiple promises, e.g. from database queries.
Use Promise.all() to wait for multiple promises.
Use try/catch to handle success and error.

i.e.

app.get('/url', async (req, res) => {
    try {
        const sql = 'SELECT * FROM mytable WHERE x = ? AND y = ? AND z = ?';
        const queries = myArray.map((item) => database.query(sql, [item.x, item.y, item.z]));
        const results = await Promise.all(queries);
        res.send(results);
    } catch (err) {
        console.error(err.stack);
        res.status(500).send(err);
    }
});

answered May 21, 2021 at 11:31

Tomalak

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2 Comments

Jogoldirus Over a year ago

It work really well , thanks ! I saw this but didn't understand how to use it , thanks for your explanation of each things

Tomalak Over a year ago

@Jogoldirus If it works well and you're using it, please tick the answer as "accepted". This will close the thread.

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