Issue in promise based recursive function

Question

I am working on AWS Lambda using nodejs environment. I have one API in which I am using recursive function for some functionality.

Actually most people say avoid recursive function but as per my functionality I need this. My functionality is as follows.

I have one table table1 in which there are two columns pid and cid which is defined as unique constraint. Which means combination of two columns should be unique.

So if I am inserting any combination in table1 and it that combination already exist then it gives me duplicate entry error which is correct as per my functionality.

So in order to handle this duplicate entry error I have used try..catch block. So in catch block I have checked if duplicate entry error occurred then I am calling one recursive function which try different combination until new entry is created in table1.

And my recursive function is promise based. but when new entry in created successfully then I am resolving the promise. But promise does not get returned from where I have called my recursive function for very first time. And because of that timeout occurs.

So please someone suggest me solution so that my promise got resolved and my functionality will continue from point where I have called my recursive function for very first time. So the timeout will not come.

I am providing my code for reference.

var mysql = require('mysql');

var con = mysql.createConnection({
    "host": "somehost.com",
    "user": "myusername",
    "password": "mypassword",
    "database": "mydatabase"
});

exports.handler = async (event, context) => {

    try {
        con.connect();
    } catch (error) {
        throw error;
        return 0;
    }

    let tableId = '';
    let count = '';

    try {

        var tempUsageData = {
            user_id: userId,
            code: code,
            platform: source,
            some_id: some_id,
            count: count
        };

        dbColumns = 'user_id, code, platform, added_on, count, some_id';
        let usageData = [
            [userId, code, source, new Date(), count, some_id]
        ];
        var tableInsert = await databaseInsert(con, constants.DB_CONSTANTS.DB_USAGE, dbColumns, usageData);
        tableId = tableInsert.insertId;
    } catch (error) {
        console.log('@@ error insert table1 @@', error);

        if (error.errno == 1062) {

            try {
                // calling recursive function here
                let newTableData = await createTableEntry(con, tempUsageData);
                tableId = newTableData.new_usage_id;
                count = newTableData.new_count;

            } catch (error) {
                console.log('Error', error);
                return 0;
            }

        } else {
            return 0;
        }
    };

    console.log('@@ EXECUTION DONE @@');
    return 1;

}

var createTableEntry = (con, dataObject) => {

    return new Promise(async function (resolve, reject) {
        console.log('createTableEntry Called for count', dataObject.count);
        try {
            var newCounter = await getDataFromDatabase(con, dataObject.some_id);

            dbColumns = 'user_id, code, platform, added_on, count, some_id';
            let tableData = [
                [userId, code, source, new Date(), Number(newCounter[0].counter + 1), some_id]
            ];
            var tableInsert = await databaseInsert(con, 'table1', dbColumns, tableData);


            let response = {
                new_table_id: tableInsert.insertId,
                new_count: Number(newCounter[0].counter + 1)
            }
            return resolve(response);

            //function not returning from here once successful entry done and timeout occures

        } catch (error) {
            console.log('@@ ERROR @@', error);

            if (error.errno == 1062) {

                console.log('@@ CALL FUNCTION AGAIN @@');

                dataObject.count = Number(newCounter[0].counter + 1);

                await createTableEntry(con, dataObject);

            } else {
                return reject(error);
            }
        }
    });
};

My final output should be message "EXECUTION DONE" should be displayed once execution done.

Please suggest me good solution for this. Thanks in advance.

`newCounter[0].counter` used where it's possible for `newCounter[0]` to be `undefined` opens your program to annoying TypeError bugs — Mulan, Jul 18 '19 at 15:02
[Never pass an `async function` as the executor to `new Promise`](https://stackoverflow.com/q/43036229/1048572)! — Bergi, Jul 18 '19 at 18:29

score 2 · Accepted Answer · answered Jul 18 '19 at 11:23

Update your catch block

catch (error) {
            console.log('@@ ERROR @@', error);

            if (error.errno == 1062) {

                console.log('@@ CALL FUNCTION AGAIN @@');

                dataObject.count = Number(newCounter[0].counter + 1);

                let result = await createTableEntry(con, dataObject);
                return resolve(result);

            } else {
                return reject(error);
            }
        }

Issue in promise based recursive function

1 Answers1