How to update field values in a document - Firebase - swift

Question

I have a collection called objects / documents of type Object that has an an array of type ObjectNotification, I am trying to update each notification.read to true.
I have a view that displays all the userNotifications from all objects in a single array self.viewModel.userNotifications.
When onAppear for the view I am trying to set each userNotification.read to true in self.viewModel.userNotifications and update the FirestoreDB.
However I am not sure the best approach to take, currently I am looping through the arrays and trying to update each userNotification in self.viewModel.objects.userNotifications then update the document in the DB, which will update self.viewModel.userNotifications as that fetches all self.viewModel.userNotifications.
But I get the following error as I am trying to change a struct, I was trying to change the value in my for in statement then called my updateObect(object) method to update the document in the DB.
Cannot assign through subscript: 'h' is a 'let' constant
.onAppear() {
// Mark as read
let read = objectManager.markNotificationsAsRead(self.viewModel.userNotifications)
self.viewModel.updateObjectNotifications(readNotifcations: read)
}
func markNotificationsAsRead(_ notifications: [ObjectNotification]) -> [ObjectNotification]{
// Mark notifications as read
var readNotifications: [ObjectNotification] = []
for n in notifications {
if n.read == false {
// Create new with true
var new = n
new.read = true
readNotifications.append(new)
}
}
// Return update notifications with read = true
return readNotifications
}
func updateObjectNotifications(readNotifcations: [ObjectNotification]) {
if let currentUser = Auth.auth().currentUser {
for h in self.objects {
for n in h.notifications {
if n.deliveredTo == currentUser.email {
for r in readNotifcations {
if r.id == n.id {
// same notif for home
// h.notifications.rem
if let index = h.notifications.firstIndex(of: n) {
h.notifications[index] = r // Cannot assign through subscript: 'h' is a 'let' constant
}
}
}
}
// update object in db
}
}
}
}
Instead of the approach above, how can I change the fields in the database ?

Answer 1

This is is a solution to the actual problem and does not address the Firebase part of the question as that was not outlined in the actual question.
I'm going to take a wild guess here as the question is incomplete but I think whatever object 'h' is in the question is a struct which contains an array property of notifications.
If so, then you can't do this within a for loop
h.notifications[index] = r
because Structs are value types, unlike classes that are reference types. That means within the for loop, the objects are a copy of the array element, not the element itself
for copyOfArrayElement in someArrayOfStructs {}
There are a few solutions; here's two. The first is to iterate over the array using an index to access the actual struct object. Suppose we have an array of fruit structs with a name and an array property
struct FruitStruct {
var name = ""
var someList = [String]()
}
var banana = FruitStruct(name: "banana", someList: ["a", "b", "c"])
var grape = FruitStruct(name: "grape", someList: ["d", "e", "f"])
var fruitsArray = [banana, grape]
then the loop to modify every fruit name to be 'Hello' and element with index of 1 within the someList to be 'World'
for i in 0..<fruitsArray.count {
fruitsArray[i].name = "Hello"
fruitsArray[i].someList[1] = "World"
}
fruitsArray.forEach { print($0.name, $0.someList) }
and the output
Hello ["a", "World", "c"]
Hello ["c", "World", "e"]
Alternately change the struct to a class (which is a reference) so you can then modify the properties directly using your existing loop.
class FruitClass {
var name = ""
var someList = [String]()
convenience init(withName: String, andArray: [String] ) {
self.init()
self.name = withName
self.someList = andArray
}
}