How can I return a count of second level collection documents in Firebase? - swift

Question

I am trying to provide a count of the number of items in the ‘Products’ collection for each user, and display this in a label on the UI of my app. This is how my Firebase database is structured:
Users
user 1
products
product 1
product 2
user 2
products
product 1
So for example, when user 1 logs in, it will display that they have 2 products, whereas when user 2 logs in, it will display that they have 1 product.
Below is my code which is used to return this data for each user.
document.reference.collection("products").get().then(function(querySnapshot) {
However, I am getting the below errors for this line of code.
Error 1 - “Cannot find 'querySnapshot' in scope”
Error 2 - “Cannot find 'function' in scope”
Here is my full method I am using to retrieve and display a count of items for the currently signed in user.
func databaseCount() {
let db = Firestore.firestore()
let user = Auth.auth().currentUser
db.collection("users").getDocuments { (snapshot, error) in
if let error = error {
print(error)
return
} else {
for document in snapshot!.documents {
let data = document.data()
let userId = data["uid"] as! String
if userId == user?.uid {
document.reference.collection("products").get().then(function(querySnapshot) {
console.log(querySnapshot.size);
let itemCount = data(querySnapshot.size) as! String
self.welcomeLabel.text = "Your item count is \(itemCount)!"
});
}
}
}
}
}
How would I go about updating my code to achieve my intended goal?

Answer 1

What i usually do in such scenarios is, When you create document in Users collection create an extra field of name cartItemCount with value 0 by default. In your case productsCount.
Users
---------user1
------------------name
------------------email
------------------productCount
------------------Products
--------------------------------product1
So when ever a document is added to Product collection of a User. Increment the value of productsCount by 1 and decrement by 1 if document is removed using the reference to that user document.
FieldValue.increment(Int64(1))
FieldValue.increment(Int64(-1))