Lambda function MySQL result not working on NodeJs 8.10 - mysql

Question

I have a code in Node 6.10 and it is working...
But If I convert it to Node 8.10 it's not working
var mysql = require("mysql");
var connection = mysql.createConnection({
host: " localhost",
user: "root",
password: "",
database: "parser_db"
});
exports.handler = async event => {
connection.connect();
let response = {
statusCode: 400,
body: { Method: "Invalid", event }
};
var readTable = "SELECT * FROM documents where id = " + mysql.escape(1);
connection.query(readTable, function(err, results, fields) {
if (err) throw err;
else {
response = {
statusCode: 200,
body: { results }
//body: { results }
};
console.log(response);
return response;
}
});
};
Can some one please help me to detect the problem. It is also not working if I do the MySQL query in separate file and return the result set.
Note : If I print the result using console.log(response) instead returning it's
showing the correct result.

Answer 1

The problem is that you are returning response from within the connection.query() callback function. That makes response the return value for the callback function, not the return value for the outer Lambda function.
One way to restructure this code is as follows:
exports.handler = async (event) => {
connection.connect();
return new Promise((resolve, reject) => {
const readTable = `SELECT * FROM documents where id = ${mysql.escape(1)}`;
connection.query(readTable, (err, results, fields) => {
if (err) {
reject(err);
} else {
resolve({statusCode: 200, body: {results}});
}
});
});
};

Answer 2

In addition to #jarmod's answer, You can also use the util.promisify method to promisify connection.query so that you can use the await keyword, to make the code simpler
const util = require('util');
exports.handler = async (event) => {
connection.connect();
const readTable = `SELECT * FROM documents where id = ${mysql.escape(1)}`;
const connQueryPromisified = util.promisify(connection.query).bind(connection);
const result = await connQueryPromisified(readTable);
return {statusCode: 200, body: {results}};
};