How do I find with reference of a MongoDB model - mongodb

Question

I am trying to find the ID of a model which is a reference to another model. I have a shopModel and a productModel that has a reference to shopModel
//shopModel
const shopSchema = mongoose.Schema({
user: {
type: mongoose.Schema.Types.ObjectId,
required: true,
ref: "User",
},
name: {
type: String,
},
description: {
type: String,
}
})
//productModel
const productSchema = mongoose.Schema(
{
shop: {
type: mongoose.Schema.Types.ObjectId,
required: true,
ref: "Shop",
},
name: {
type: String,
required: true,
},
//and more
Now my question is do I use await Product.find({ shop: "shopID"}) or await Product.findById(req.params.id). The current route is /shop/shopID. Note that there will be multiple shops and multiple products in one shop, but no shop will have the same productID. The problem now is I tried to console.log await Product.findById(req.params.id) and turned up undefined. Any help would be appreciated. Thank you.
UPDATE
//current productController
const getProducts = AsyncHandler(async (req, res) => {
const shopID = await Product.findOne({
shop: req.params.id,
});
console.log(shopID._id);
const products = await Product.find({
shop: mongoose.Types.ObjectId(req.params.id),
});
res.json({ products });
});
The output log is the product ID
//new productController
const getProducts = AsyncHandler(async (req, res) => {
const shopID = await Shop.findOne({
shop: req.params.id,
});
console.log(shopID._id);
const products = await Product.find({
shop: mongoose.Types.ObjectId(req.params.id),
});
res.json({ products });
});
Now I am getting the shop ID. I created 2 test shops, shop1 has all the products, while shop2 has none. The current problem is the log for both shops is giving the same id.