Mongoose loop through findOneAndUpdate condition statement - mongodb

Question

I want to know if this part of code can be written differently, only with Mongoose helper methods of models ? Can I return a success and error if no stock are greater then 0 ?
ProductSchema.statics.substractStock = function (products) {
_.map(products, updateStock)
function updateStock(o) {
mongoose.model('Product').findById(o._id, function (err, product) {
return product
}).then(function(productDB){
if(productDB.stock > o.stock && productDB.stock > 0){
mongoose.model('Product').findOneAndUpdate(o._id, {$inc: {stock: -(o.stock)}}, {},
function (err, doc) {
//return success ??
}
);
} else {
//return 'no update'
}
});
}
};

Answer 1

This could be done with an atomic update where you can ditch the initial findById() call and include the comparison logic
if (productDB.stock > o.stock && productDB.stock > 0) { ... }
within the query as in the following:
function updateStock(o) {
mongoose.model('Product').findOneAndUpdate(
{
"_id": o._id,
"$and": [
{ "stock": { "$gt": o.stock } } ,
{ "stock": { "$gt": 0 } }
]
},
{ "$inc": { "stock": -(o.stock) } },
{ "new": true }, // <-- returns modified document
function (err, doc) {
// check whether there was an update
}
);
}