CODEWITHSUNDEEP
javascriptmysqlnode.jsexpress
Fabricio Ganzert
Fabricio Ganzert

Reputation: 89

Promises problem: Trying to wrap mysql queries to use it on NodeJS / Express

My goal is to wrap MySQL queries, pass the parameters to a function and another function does the MySQL job, returning the results.

Here's my code so far:

//mysql lib
var mysql = require('mysql');

//database credentials
exports.pool = mysql.createPool({
connectionLimit: 50,
host: 'localhost',
user: 'root',
password: 'password',
database: '_app',
debug: false
});

//my wrapper =(
var returnResultset = exports.returnResultset = function (qry) {
return new Promise(function (resolve, reject) {
    try {

        mysql_.pool.getConnection(function (err, connection) {

            if (err) {
                console.log("Error on function returnResultset - MYSQL ERROR: " + err);
                return reject(err);
            }

            connection.query(qry, [], function (error, results, fields) {

                connection.release();

                if (error) {
                    console.log("Error on function returnResultset - MYSQL ERROR: " + error);
                    return reject(error);
                }

                return resolve(results);

            });

        });

    }
    catch (e) {
        console.log('error:' + e);
    }
});

};

//wrapper function for testing purposes
var selectOneField = exports.selectOneField = function (tbl, field, pk, pkval) {

var qry_ = "SELECT  " + field + " FROM " + tbl + " WHERE " + pk + " = '" + pkval + "'";

returnResultset(qry_).then(function (results) {
    return results;
}, function (error) {
    console.log("Error: " + error);
})

};

//...and on another page I want to be able to receive the results from the function above:

var isExpired = exports.isExpired = function (cod) {

var rtf = db_.selectOneField('view_expiredusers', 'cod', 'cod', cod);

console.log(rtf);

return rtf;

};

The code above returns undefined. I can't get to make this function working properly.

I have tried console.log(results). The query works like a charm. Only thing I can't get to work is to catch the result from an external function.

Any thoughts? Thanks in advance!

Upvotes: 1

Views: 286

Answers (2)

Nithya Rajan
Nithya Rajan

Reputation: 4884

You should return the promise and chain it inside isExpired function.

//wrapper function for testing purposes
var selectOneField = exports.selectOneField = function (tbl, field, pk, pkval) {

var qry_ = "SELECT  " + field + " FROM " + tbl + " WHERE " + pk + " = '" + pkval + "'";

return returnResultset(qry_);

};

//...and on another page I want to be able to receive the results from the function above:

var isExpired = exports.isExpired = function (cod) {

return db_.selectOneField('view_expiredusers', 'cod', 'cod', cod)



};

When you call the isExpired in other files you should use the then method of the promise and return the results. do it as follows

var cod_customer = 1;
var isexpired;
 isExpired(cod_customer).then(function (results) {
        isexpired = results;
        console.log(isexpired);
    }, function (error) {
        console.log("Error: " + error);
    });

Upvotes: 2

arizafar
arizafar

Reputation: 3122

you are not returning the promise in selectOneField function it must return the promise and also you cant simply do

rtf = db_.selectOneField('view_expiredusers', 'cod', 'cod', cod);

.you will have to use async-await or then

Must be handled this way

//wrapper function for testing purposes
var selectOneField = exports.selectOneField = function (tbl, field, pk, pkval) {

var qry_ = "SELECT  " + field + " FROM " + tbl + " WHERE " + pk + " = '" + pkval + "'";

return returnResultset(qry_).then(function (results) {
    return results;
}).catch(error) {
    console.log("Error: " + error);
})

};

//...and on another page I want to be able to receive the results from the function above:

var isExpired = exports.isExpired = function (cod) {

var rtf = db_.selectOneField('view_expiredusers', 'cod', 'cod', cod).then(rtf => {
console.log(rtf);

return rtf;
});


};

Upvotes: 1

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