res.end() gets executed before the promise finishes - node.js

Question

My basic POST API makes a call to database , first to authenticate user and then to authentic if the products provided are true. But before productValidation can complete, res.end() is being executed.
As output, I get ::
"validated object"
"stopping the res"
"validated object"
Whereas I am trying to validated and add each cartItem to database and only then send a success response to client.
const express = require("express");
const app = express();
const router = express.Router();
var connection = require("./../database/serverConnector");
router.get("/:userId", (req, res, next) => {
connection.query(
"SELECT * FROM cart_items AS c INNER JOIN product AS p ON c.product_id = p.id WHERE user_id = ?",
[req.params.userId],
function (error, results, fields) {
if (error) throw error;
else {
console.log("Query made for cart of user " + req.params.userId);
res.status(200).send(results);
}
}
);
});
router.post("/:userId", userValidate, (req, res, next) => {
multipleProductValidation(req, res, next).then(function (data) {
res.end();
console.log("stopping the res");
});
// .catch(error){
// console.log(error);
// }
});
function userValidate(req, res, next) {
connection.query(
"SELECT * from user where id = ?",
[req.params.userId],
function (error, user, fields) {
if (error) {
res.status(500).json({
message: error.sqlMessage,
});
} else {
if (user.length == 0) {
res.status(404).json({
message: "User not found with ID " + req.params.userId,
});
} else next();
}
}
);
}
function multipleProductValidation(req, res, next) {
return new Promise(function (resolve, reject) {
req.body.cartItems.forEach((item, i) => {
productValidate(item, req, res, next).then(function (data) {
resolve(data);
console.log("validated object");
//next();
});
});
});
}
function productValidate(item, req, res, next) {
return new Promise(function (resolve, reject) {
connection.query(
"SELECT * from product where id = ?",
[item.product_id],
function (error, product, fields) {
if (error) {
res.status(500).json({
message: error.sqlMessage,
});
} else {
if (product.length == 0) {
res.status(404).json({
message: "Product not found with ID " + item.product_id,
});
resolve(false);
} else {
connection.query(
"INSERT INTO cart_items (product_id,user_id,size,quantity) VALUES (?,?,?,?)",
[item.product_id, req.params.userId, item.size, item.quantity],
function (error, results, fields) {
if (error) {
res.status(500).json({
message: error.sqlMessage,
});
} else {
res.statusText =
"Items added to cart for User " + req.params.userId;
resolve(true);
}
}
);
}
}
}
);
});
}
module.exports = router;

Answer 1

So what is happening here is that you are calling resolve in your multipleProductValidation before you finish processing all the products.
something like this should fix your problem
function multipleProductValidation(req, res, next){
return new Promise(function(resolve, reject) {
let promiseArr = req.body.cartItems.map(item => productValidate(item, req, res, next))
Promise.all(promiseArr).then(values => resolve(values))
}
)}