How to update an array data in database using NodeJs Async?

Question

I am new to NodeJs and I'm finding the Non Blocking and Asynchronous nature of JS extremely difficult to understand and handle,
I have a piece of code which is supposed to Iterate an array
and for every iteration, I'm supposed to make a DB update.

Can someone provide the correct implementation of Async library functions and help fix my code?

Code example -

function updateFunction(conn, requestBody, callback) {

    let arr = [];

    async.each(requestBody.arr, function(item, callback) {
        let sqlData = []
        let columns = "";

        if(item.columnData != null){
            sqlData.push(item.columnData);
            columns += "`columnName` = ?,";
        }

        if(columns != ''){
            columns = columns.substring(0,columns.length-1);

            let sqlQuery = 'UPDATE someTable SET '+columns
            +' WHERE id = "' + item.id + '"';

            conn.query(sqlQuery, sqlData, function (err, result) {
                if (err) {
                    return callback(err, false);
                }
            })
        }
        else{
            return callback(null, false);
        }
        columns = "";
        sqlData = [];
    },
    function(err, results) {
    //Code never reaches here, don't know why       
     if (err) {
            return callback(err, false);
        }
        else{
           return callback(null, true);
        }
    });
} // END

I would go with ES6 async and await, or I would prefer using axios.. they are certainly easy and reliable — Gopi Gorantala
– Gopi Gorantala, Commented Feb 17, 2019 at 13:14
Can help with some code snippet? The conn.query part is becoming a nightmare in my code, not able to handle it. — Dev1ce
– Dev1ce, Commented Feb 17, 2019 at 13:15

maazadeeb · Accepted Answer · 2019-02-19 02:18:58Z

1

During your database query call, on a successful query your callback is not called, therefore causing your code to never reach the final callback.

You will want to add another return statement after your if (err) { return callback(err); } to let async know your database query is finished.

And another thing, according to the docs, the async each method's final callback does not invoke with results in its callback.

A callback which is called when all iteratee functions have finished, or an error occurs. Invoked with (err).

Therefore, it is not required for you to pass a value into the callback statement within your iteratee function.

Modify your code to do this and it will work.

conn.query(sqlQuery, sqlData, function (err, result) {
    if (err) {
        return callback(err);
    }

    return callback(null);
})

Hope this helps.

edited Feb 19, 2019 at 2:18

maazadeeb

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answered Feb 19, 2019 at 2:04

Zheliang Tan

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2 Comments

Dev1ce Over a year ago

Will adding the callback in successful DB update break the loops or just iterate onto the next element of the array?

Zheliang Tan Over a year ago

Actually neither. The each method does not loop like a typical forEach loop for arrays. If you would like your array to loop sequentially you should use eachSeries method instead.

Gopi Gorantala · Accepted Answer · 2019-02-17 13:22:06Z

0

conn.query(sqlQuery, sqlData, async function (err, result) {
                if (err) {
                    return  await callback(err, false);
                }
            })

Something like this.. so the function callback is async here and we gave await which actually waits until the return call is finished..

answered Feb 17, 2019 at 13:22

Gopi Gorantala

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