UnhandledPromiseRejectionWarning when adding a new record to DB - node.js

Question

I am trying to add new records to my MongoDB database. The records come in the form of an array, and then, for each record, I add it as a new item to MongoDB.
The problem is that every time I try to add some records (30-50 records) I get this message:
UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch()
followed by this one:
UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
This is the snippet I use for adding records:
// update the blacklist with a new entry
router.post("/updateBlacklist", async (req, res) => {
req.body.product_id.forEach(async element => {
const blacklistItem = new Blacklist({ product_id: element });
try {
const savedItem = await blacklistItem.save();
res.json(savedItem);
} catch (err) {
console.log(err);
res.json({ message: err });
}
});
});
The same warning appears also when I try to download some photos using this function:
router.post("/product_ids", async (req, res) => {
await downloadPhotos(req.body.items_id);
});
the function I call inside this route:
const axios = require("axios");
const download = require("./utils/download");
const downloadPhotos = async itemsIDs => {
try {
console.log(itemsIDs.length);
await itemsIDs.forEach(ID => {
axios
.get(
`https://${process.env.SHOPIFY_API_KEY}:${
process.env.SHOPIFY_PASSWORD
}#blablabla.myshopify.com/admin/products/${ID}/images.json?fields=id, src`
)
.then((req, res) => {
console.log(req.data.images[0].src);
download(req.data.images[0].src, req.data.images[0].id, 3000);
});
});
} catch (err) {
console.log(err);
}
};
and the download function:
const Fs = require("fs");
const Path = require("path");
const Axios = require("axios");
async function downloadImage(url, filename, timeout) {
const appDir = Path.dirname(require.main.filename);
const path = Path.resolve(appDir, "images", `${filename}.jpg`);
const writer = Fs.createWriteStream(path);
const response = await Axios({
url,
method: "GET",
responseType: "stream",
timeout: timeout
});
response.data.pipe(writer);
return new Promise((resolve, reject) => {
writer.on("finish", resolve);
writer.on("error", reject);
});
}
module.exports = downloadImage;
What am I doing wrong in this approach?

Answer 1

This error:
UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
It's because of these lines:
res.json(savedItem);
res.json({ message: err });
You're running these lines several times, because they are inside the loop, you can't respond a request more than once because the connection it's closed after the first call.
Try with this:
router.post("/updateBlacklist", async (req, res) => {
const savedList = [];
req.body.product_id.forEach(async element => {
const blacklistItem = new Blacklist({ product_id: element });
try {
const savedItem = await blacklistItem.save();
savedList.push(savedItem)
} catch (err) {
console.log(err);
savedList.push({ message: err });
}
});
res.json(savedItem);
});
UPDATE (suggestion):
router.post("/updateBlacklist", async (req, res) => {
const items = req.body.product_id.map(element =>
new Blacklist({ product_id: element })
});
const result = await Blacklist.insertMany(items); // not sure about the syntax
res.json(result);
});