null values when fetching data from database in nodejs - node.js

Question

am new to nodeJS and am having some problem understanding how async and await works. Here is my code am using to fetch data from my database:
const sql = require('mssql');
const config = require('./config');
var Student = require('./student');
module.exports.getAllStudents = async function getAllStudents(){
var studentArray = new Array();
console.log('dbconnection');
var conn = new sql.ConnectionPool(config.dbConfig[0]);
conn.connect()
.then(()=>{
var req = new sql.Request(conn);
req.query('SELECT * from student').then((recordset)=> {
var dataset = recordset.recordset;
for(var index = 0; index<dataset.length; index++){
var student = new Student(dataset[index].student_id , dataset[index].first_name, dataset[index].last_name, dataset[index].student_address , dataset[index].age);
studentArray.push(student);
}
conn.close();
}).catch( (error) =>{
console.log("An error has occured while executing your query ");
console.log(error);
});
})
.catch( (error)=> {
console.log("An error has occured while trying to connect to the database : ");
console.log(error);
});
return studentArray;
}
and here is the endpoint where i made a call to fetch all the students:
app.get('/getAllStudents' , function(req , res){
var studentArr = new Array();
studentArr = query.getAllStudents();
console.log('====================================');
//console.log(studentArr); //this prints undefined
//console.log('length:======' + studentArr.length);
//var json = JSON.stringify(studentArr);
res.status(200);
res.send('got all students');
})
am trying to understand how to counter this error, what needs to be done to wait for my query to get the results then prints the student array. Could anybody explain to me what needs to be done and why it is not working ?

Answer 1

Because it's asynchronous you should return a promise then resolve() the results
const sql = require('mssql');
const config = require('./config');
var Student = require('./student');
module.exports.getAllStudents = function getAllStudents() {
return new Promise((resolve, reject) => {
var studentArray = new Array();
console.log('dbconnection');
var conn = new sql.ConnectionPool(config.dbConfig[0]);
conn.connect()
.then(()=>{
var req = new sql.Request(conn);
req.query('SELECT * from student').then((recordset)=> {
var dataset = recordset.recordset;
for(var index = 0; index<dataset.length; index++){
var student = new Student(dataset[index].student_id , dataset[index].first_name, dataset[index].last_name, dataset[index].student_address , dataset[index].age);
studentArray.push(student);
}
resolve(studentArray);
conn.close();
}).catch( (error) =>{
console.log("An error has occured while executing your query ");
console.log(error);
reject(error);
});
})
.catch( (error)=> {
console.log("An error has occured while trying to connect to the database : ");
console.log(error);
reject(error);
});
});
}
Then add async to your function and await to query.getAllStudents()
app.get('/getAllStudents' , async function(req , res){
var studentArr = new Array();
studentArr = await query.getAllStudents();