MongoDB $elemMatch updates the wrong element when an additional query is present - mongodb

Question

I am facing a weird issue with MongoDB. I am using the official mongo client to use it from NodeJS.
My data sort of looks like this
// collection "products"
{
shop: 'ShopID1',
customer: ['CustomerID1', 'CustomerID2'],
products: [
{product: 'ProductID1', productCount: 10, customer: ['CustomerID1']},
{product: 'ProductID2', productCount: 5, customer: ['CustomerID2']},
]
}
Now, I want to remove 'CustomerID2' from the 2nd product object if it exists on both the outer customer array and in the inner customer array of the 2nd product object.
I can do it with the following query,
const productID = 'ProductID2';
const customerID = 'CustomerID2';
db
.collection('products')
.findOneAndUpdate(
{
shop: 'ShopID1',
// customer: {
// $in: [customerID]
// },
products: {
$elemMatch: {
product: productID,
customer: {
$in: [customerID]
}
}
},
},
{
$inc: {
'products.$.productCount': 1
},
$pull: {
'products.$.customer': customerID,
customer: customerID
}
},
);
The problem is, if I uncomment the commented part above, it updates the first product object, which is wrong. I can't find the reason why this happens as my knowledge of Mongo is limited. It seems to me the uncommented part is only adding an additional constraint that should not affect the update operation.
I would also appreciate any feedback on whether this is the correct way to achieve my stated goal. Thanks

Answer 1

//data preparation check
> db.custProducts.find().pretty();
{
"_id" : ObjectId("5f5e6d68598d922a1e6eff5c"),
"shop" : "ShopID1",
"customer" : [
"CustomerID1",
"CustomerID2"
],
"products" : [
{
"product" : "ProductID1",
"productCount" : 10,
"customer" : [
"CustomerID1"
]
},
{
"product" : "ProductID2",
"productCount" : 5,
"customer" : [
"CustomerID2"
]
}
]
}
//code to remove customerID2 field in both outer array and inner object
//.$. to be used to traverse the document object
> db.custProducts.aggregate([
... {$unwind:"$customer"},
... {$unwind:"$products"},
... {$match:{
... "shop": "ShopID1",
... "customer": "CustomerID2",
... "products.product": "ProductID2"
... }
... }
... ]).forEach(function(doc){
... print("prod: ",doc.products.product);
... print("cust: ",doc.customer);
... db.custProducts.update(
... {"shop": doc.shop, "products.product": "ProductID2" },
... {$pull:
... {
... customer:{$in:[doc.customer]},
... "products.$.customer":{$in:[doc.customer]}
... }
... }
... );
... }
... );
prod: ProductID2
cust: CustomerID2
//check the output of the update execution.
> db.custProducts.find().pretty();
{
"_id" : ObjectId("5f5e6d68598d922a1e6eff5c"),
"shop" : "ShopID1",
"customer" : [
"CustomerID1"
],
"products" : [
{
"product" : "ProductID1",
"productCount" : 10,
"customer" : [
"CustomerID1"
]
},
{
"product" : "ProductID2",
"productCount" : 5,
"customer" : [ ]
}
]
}
>
//further,you can add other logic like $inc in the above code