How do I get back data from a database using express.js without the result being undefined - sql

Question

`I've been trying to display a database product with react but none of my approaches seem to work.
This is my node.js/express code :
const express = require('express');
const database = require('./config/database');
const bodyParser = require('body-parser');
const cors = require('cors');
const PORT = 3001;
const app = express();
app.use(express.json());
app.use(cors());
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/products/:productId', (req, res) => {
console.log('request recieved');
const productId = req.params.productId;
const query = `SELECT * FROM products WHERE product_id = ${productId}`;
database.query(query, (err, result) => {
if (err) console.log(err);
console.log(result);
res.send(result);
});
});
app.listen(PORT, 'localhost');
I tried to fetch and log it with axios but the results are undefined :
const productId = params.productId;
const url = `/product/${productId}`;
const [{data, loading, error}] = useAxios(url);
console.log(data);
I also tried the regular approach :
const fetchProduct = async (url) => {
try {
const response = await fetch(url);
console.log(response);
const data = await response.json();
console.log(data);
} catch(err) {
console.log(err);
}
return data;
}
const product = fetchProduct(url);
console.log(product);`
Some help would be appreciated

Answer 1

What if you create an arrow-function that it returns a Promise
const getById = (productId) => {
const query = `SELECT * FROM products WHERE product_id = ${productId}`;
return new Promise((resolve, reject) => {
database.query(query, (err, result)=> {
err ? reject(err): resolve(result)
})
})
}
as our getById arrow-function returns a promise we need to async/await on it, so the app.get will be like this
app.get('/products/:productId', async(req, res) => {
console.log('request recieved');
const productId = req.params.productId;
const product = await getById(productId)
res.status(200).send(product)
});
One more thing, in your code you wrote
app.use(express.json());
and
app.use(bodyParser.json());
those two instruction do the SAME THING, so you need to delete one of them, and it better be the bodyParser one, because the body-parser is just deprecated and you don't need to install it, you just need to add
app.use(express.json())
app.use(express.urlencoded({ extended: true }))