Populate() of Populate() in Mongoose for querying to match $in array - node.js

Question

I am developing an eCommerce web App. I am experiencing a problem described as follows.
I am suppose to run a cron job. When a brand adds a new product to the system, every shop that sells that brand will automatically show the newly added product by the brand. The Cron Job will run every morning at 12 to go through all the shops individually and will add the newly added product.
Now the shop will have an array of products. From that array of products, I need to fetch all the unique brands to compare it with the brand of newly added product. If the brand of newly added product exists in the shop.products[], then that product._id will be pushed in that array.
Here is my code.
CRON JOB CODE :
module.exports.newProductAddedCronJob = function(req,res){
// console.log("New Products Added Cron Job");
ProductReplacement.find({
status: "Pending",
"type": "new"
})
.populate("primaryProduct")
.exec(function(err,newProducts){
if(err) return res.status(500).send({err});
if(newProducts.length < 1) return res.status(404).send({err : "No New Products Added."});
async.forEachSeries(newProducts,function(item){
console.log("New Product : ", item.primaryProduct.brand._id);
Shop.find({
"products.brand._id" : {
$in: [item.primaryProduct.brand._id]
}
})
.populate("products")
.exec(function(err,shopsWithBrand){
console.log("SHOPS WITH Brand "+item.primaryProduct.brand._id + " Total = "+shopsWithBrand.length);
console.log("SHOPS WITH BRAND : ",shopsWithBrand);
for(var j = 0 ; j < shopsWithBrand.length; j++){
console.log("Shop = "+shopsWithBrand[i].name);
}
});
},function(err,data){
console.log("Final Callback!")
if(err) return res.status(500).send({err})
res.send({newProducts});
})
})
}
ProductReplacement is used for multiple purposes. In that particular schema, the type = "new" means the products that are newly added by a brand and status = "Pending" means, it is not yet processed.
var Product = new mongoose.Schema({
brand: {
_id: mongoose.Schema.Types.ObjectId,
name: {
type: String,
required: true
},
nameSlug: {
type: String,
required: true
},
images: [Image]
}
});
Brand Schema :
var Brand = new mongoose.Schema({
name: {
type: String,
minlength: 2,
maxlength: 30,
required: true
},
images: [{
src: String,
alt: String,
type: {
type: String,
enum: imageTypes,
validate: validators.isIn({message: 'The image type should be one of the following: (' + imageTypes + ')'}, imageTypes)
}
}]
});
Shop Schema :
var Shop = new mongoose.Schema({
products: [{
_id: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Product'
},
stock: {
type: Number,
required: true
},
price: {
type: Number
}]
});
ProductReplacement Schema :
var ProductReplacement = new mongoose.Schema({
primaryProduct : {
type: mongoose.Schema.ObjectId,
ref: 'Product'
},
duplicateProduct: {
type: mongoose.Schema.ObjectId,
ref: 'Product'
},
"type": {
type: String,
required: true,
default: "merge"
},
created_at : {
type: Date,
required: true,
default: Date.now
},
status: {
type: String,
required: true,
default: "Pending"
}
});
So all I need is Shop.products.brand.id to compare it with the brand ID of the newly added product. If they match, I will push it into the array of products in that particular shop.
But I am not able to get shops using the query.
The last option of iterating through all the products of each shop one by one is certainly open. But I was wondering if there could be some way to do the same using query.