Database returned value is undefined in Node JS

Question

I have a encountered a problem while learning NodeJS. I am new to javascript so can anybody explain this to me.

I am calling a function from index.js which will returns values fetched from database. But I am getting undefined object on return.

index.js

const cron = require('node-cron');
const app = require('./app');
const port = process.env.PORT || 3000;
require('dotenv').config();

const { getRecentData } = require('./service/getRecentData')

var prev_id = 0;
cron.schedule('*/10 * * * * *', async() => {
    var row = await getRecentData();
    console.log(row);
    var new_id = row["id"];
    if (new_id == prev_id){
        new_id = prev_id;
    }
    else{
        console.log(row["date_time"]);
        prev_id = new_id;
    }
})

app.listen(port, () => {
  console.log(`Listening: http://localhost:${port}`);
});

getRecentData.js

const e = require("express")

const { Client } = require('pg');

const client = new Client({
    user: 'postgres',
    host: 'localhost',
    database: 'database',
    password: 'postgres',
    port: 5432,
});

client.connect();

const getRecentData = async () => {
  const query = `
    SELECT *
    FROM test_table order by id desc limit 1
    `;

   const recentData =  await client.query(query, (err, res) => {
        if (err) {
            console.error(err);
            return;
        }
        return res.rows; 
  });

  return recentData;
}


module.exports = {
  getRecentData
}

But I am getting undefined object in index.js when calling getRecentData() function.

Amir Saleem · Accepted Answer · 2021-03-26 05:30:23Z

2

You need to understand that await works only with Promises. If the function returns a Promise, you can use await. All async functions return a Promise. In your case, client.query is not returning a promise, it has a callback which has it's own execution context, hence return recentData statement is executing before the completion of the client.query method. You can modify your getRecentData method like this

const getRecentData = () => {
    return new Promise((resolve, reject) => {
        const query = `SELECT * FROM test_table order by id desc limit 1`;
        client.query(query, (err, res) => {
            if (err) {
                console.error(err);
                reject(err);
                return;
            }
            resolve(res);
        });
    });
};

answered Mar 26, 2021 at 5:30

Amir Saleem

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Comments

Shailendra · Accepted Answer · 2021-03-26 09:49:55Z

0

don't use recentData variable

await client.query(query, (err, res) => {
        if (err) {
            console.error(err);
            return;
        }
        if(res){
             return res.rows; 
        }
  });

answered Mar 26, 2021 at 9:49

Shailendra

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