How to delete ($pull) nested array elements with property value null in arrays with more than one element - mongodb

Question

I would like to delete ($pull) nested array elements where one of the element's properties is null and where the array has more than one element.
Here is an example. In the following collection, I would like to delete those elements of the Orders array that have Amount = null and where the Orders array has more than one element. That is, I would like to delete only the element with OrderId = 12, but no other elements.
db.TestProducts.insertMany([
{
ProductDetails: { "ProductId": 1, Language: "fr" },
Orders: [
{ "OrderId": 11, "Amount": 200 },
{ "OrderId": 12, "Amount": null }
]
},
{
ProductDetails: { "ProductId": 2, Language: "es" },
Orders: [
{ "OrderId": 13, "Amount": 300 },
{ "OrderId": 14, "Amount": 400 }
]
},
{
ProductDetails: { "ProductId": 3, Language: "en" },
Orders: [
{ "OrderId": 15, "Amount": null }
]
}
]);
The following attempt is based on googling and a combination of a few other StackOverflow answers, e.g. Aggregate and update MongoDB
db.TestProducts.aggregate(
[
{ $match: { "Orders.Amount": { "$eq": null } } },
{ $unwind: "$Orders" },
{
"$group": {
"_id": {
ProductId: "$ProductDetails.ProductId",
Language: "$ProductDetails.Language"
},"count": { "$sum": 1 }
}
},
{ "$match": { "count": { "$gt": 1 } } },
{ "$out": "temp_results" }
],
{ allowDiskUse: true}
);
db.temp_results.find().forEach((result) => {
db.TestProducts.updateMany({"ProductDetails.ProductId": result._id.ProductId, "ProductDetails.Language": result._id.Language },
{ $pull: { "Orders": {"Amount": null } }})
});
This works, but I am wondering if it can be done in a simpler way, especially if it is possible to delete the array elements within the aggregation pipeline and avoid the additional iteration (forEach).

Answer 1

You can check these conditions in the update query, check 2 conditions
Amount is null
check the expression $expr condition for the size of the Orders array is greater than 1
db.TestProducts.updateMany({
"Orders.Amount": null,
"$expr": {
"$gt": [{ "$size": "$Orders" }, 1]
}
},
{
"$pull": {
"Orders": { "Amount": null }
}
})
Playground

Answer 2

an example
an example might help:
let feed = await Feed.findOneAndUpdate(
{
_id: req.params.id,
feeds: {
$elemMatch: {
type: FeedType.Location,
locations: {
$size: 0,
},
},
},
},
{
$pull: {
feeds: { locations: { $size: 0 }, type: FeedType.Location },
},
},
{ new: true, multi: true }
);