How to show list of field values of a collection of objects - node.js

Question

I am making an API that shows a collection of ads with MongoDB and Node.js
I need to display the list of collection tags in a JSON string.
Example: 'home', 'mobile', 'motor'
This is the API initializer code:
const readline = require('readline');
const Product = require('./models/Product');
async function main() {
const advance = await question('Are you sure to continue with the deletion of the database? (yes or no) ')
if (!advance) {
process.exit();
}
const connection = require('./lib/connectMongoose')
await initProducts();
connection.close();
}
async function initProducts() {
const deleted = await Product.deleteMany();
console.log(`Remove ${deleted.deletedCount} products.`);
const inserted = await Product.insertMany([
{name: 'Table', sale: true, price: 150, photo: 'Table.png', tags: ['home']},
{name: 'Iphone 13 pro', sale: false, price: 950, photo: 'Iphone 13 pro.png', tags: ['mobile']},
{name: 'Car Mini Cooper', sale: true, price: 1000, photo: 'Car Mini Cooper.png', tags: ['motor']}
]);
console.log(`Create ${inserted.length} products.`)
}
main().catch(err => console.log('Hubo un error', err))
function question(text) {
return new Promise((resolve, reject) => {
const interface = readline.createInterface({
input: process.stdin,
output: process.stdout
});
interface.question(text, answer => {
interface.close();
if (answer.toLowerCase() === 'yes') {
resolve(true);
return;
}
resolve(false);
})
})
}
I need to find a MongoDB method that allows me to show when the API route calls the list that shows in JSON format all the tags that the collection includes

Answer 1

If I've understood correctly, one option is $unwind the tags array to get all tags as strings and be able to $group adding to a set to avoid duplicates.
db.collection.aggregate([
{
"$unwind": "$tags"
},
{
"$group": {
"_id": null,
"tags": {
"$addToSet": "$tags"
}
}
}
])
I think this works but $unwind and $group the entire collection is not always a good idea. It may be a slow process.
Example here