Trouble with async mongoose queries - node.js

Question

This is the array that i get from my database, let's call it product_list
{
"seller": "5cee0e69f67e171ac8ef14c7",
"products": [...]
},
{
"seller": "5d1c36910aec8934cefdda8e",
"products": [...]
}
And i want to send the same array but transforming the seller field into the complete seller object. In the given example would be these ones.
{
"_id": "5cee0e69f67e171ac8ef14c7",
"name": "Will"
},
{
"_id": "5d1c36910aec8934cefdda8e",
"name" : "Jess"
}
So my desired output would be
{
"seller": {
"_id": "5cee0e69f67e171ac8ef14c7",
"name": "Will"
},
"products": [...]
},
{
"seller": {
"_id": "5d1c36910aec8934cefdda8e",
"name": "Jess"
},
"products": [...]
}
I tried the following
product_list.forEach(element => {
User.findById(element.seller, function(err, user){
element.seller = user;
};
});
What i'm trying is to take all the seller ids from the product_list object, convert it to the complete object with User.findById, and return the updated product_list. But the problem is that i'm not to good with asynchronous code, and since the mongoose calls are callbacks when i return the object with res.json(product_list), the mongoose query is not finished and i receive the object without the modification.
I tried promises and awaits but im not getting any result.
I hope you understand my explanation, and thank you very much.

Answer 1

You can try this approach, wrap User.findById and you can use the async / await pattern.
// Wrapper function for User.findById. We could use utils.promisify for this.
function getUserById(id) {
return new Promise((resolve, reject) => {
User.findById(id, (err, result) => {
if (err) {
reject(err);
} else {
resolve(result);
}
})
});
}
async function getSalesDetails(productList) {
for(let product of productList) {
let userDetails = await getUserById(product.seller);
product.seller = userDetails;
}
return productList;
}
async function testGetSalesDetails() {
let productList = [{
"seller": "5cee0e69f67e171ac8ef14c7",
"products": [1,2,3]
},{
"seller": "5d1c36910aec8934cefdda8e",
"products": [4,5,6]
}];
let productListWithSeller = await getSalesDetails(productList);
console.info("Product list (with seller): ", productListWithSeller);
}
testGetSalesDetails();
You could also use utils.promisify to generate the getUserById function (it's very handy!), for example:
const getUserById = util.promisify(User.findById);