CODEWITHSUNDEEP
mysqlnode.js
h20002000
h20002000

Reputation: 73

Cannot get variable from sql query in Node

Sorry, I read about handling async functions in order to get variable names from them but I am not sure what I am doing wrong and how to handle it.

    for(let j = 0; j < ga.length; j++) {
    var sql = "SELECT * FROM matches WHERE clh = '"+ga[j]+"'"
    const dbq = db.query(sql, function(err, result) {
        if (err) console.log(err);
        var gs1 = 0;
        var gs2 = 0;
        var pts1 = 0;
        var w1 = 0;
        var d1 = 0;
        var l1 = 0;
        for (let i = 0; i < result.length; i++) {
            gs1 += result[i].gsh;
            gs2 += result[i].gsa;
            const r = mgs1(result[i].gsh, result[i].gsa);
            if (r == 3) w1 += 1;
            if (r == 1) d1 += 1;
            if (r == 0) l1 += 1;
            var gd1 = gs1 - gs2;
            var r1 = [result[i].clh, result.length, w1, d1, l1, gs1, gs2, gd1 ];
        }
        
        gs4.push(r1);
        
        if (gs4.length == 6) {
            return gs4;
        }
    })
}
}

This function returns the array that I want but I am not sure how to access it outside the db.query block. I read posts about handling variables from async functions but I just can't seem to do it in this example. Thanks a lot in advance

Upvotes: 1

Views: 230

Answers (2)

Danizavtz
Danizavtz

Reputation: 3270

If you would like to query the database the correct way, you should use the embedded functions that comes with database driver. For string interpolation and returning data for your functions.

   exports.lookupLogin = (req, res, next) => {
        let sql = 'SELECT e.employee_id, e.login, e.password FROM employee e WHERE e.login=?';
        postgres.client.query(sql, [req.body.login], (error, result, fields) => {
            if (err) {
                return res.status(500).json({ errors: ['Could not do login'] });
            }

            res.status(200).json(result.rows);
        });
    };

For more information you can check the mysql documentation to use with nodejs.

Upvotes: 0

O. Jones
O. Jones

Reputation: 108641

I guess you have defined const gs4 = [] somewhere in code you did not show us. That's part of the answer to your question: it will be populated after your callback from db.query() completes.

The rest of the answer: it is not populated until after the callback completes. Also, the return from inside your callback is meaningless; it just returns to db.query() .

Also, db.query() returns to its caller instantly, long before it calls its callback. So your loop tries to run multiple queries concurrently. I guess the result in gs4 will accumulate the results from all the queries.

With respect, I believe a quick jump up the learning curve for Promises or async / await lies in your near future.

This may help : node.js mysql query in a for loop

Upvotes: 1

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