Removing an array item from Firestore - swift

Question

I've spent days researching this including various answers like: Firebase Firestore: Append/Remove items from document array
but can't work out how to actually get this working.
I have two structs:
struct TestList : Codable {
var title : String
var color: String
var number: Int
}
struct TestGroup: Codable {
var items: [TestList]
}
I am able to add data using FieldValue.arrayUnion:
#objc func addNewItem() {
let testList = TestList(title: "Testing", color: "blue", number: Int.random(in: 1..<999))
let docRef = FirestoreReferenceManager.simTest.document("abc")
docRef.updateData([
"items" : FieldValue.arrayUnion([["title":testList.title,
"color":testList.color,
"number":testList.number]])
])
}
The above works as reflected in the Firestore dashboard:
But if I try and remove one of the items in the array, it just doesn't work.
#objc func removeItem() {
let docRef = FirestoreReferenceManager.simTest.document("abc")
docRef.getDocument { (document, error) in
do {
let retrievedTestGroup = try document?.data(as: TestGroup.self)
let retrievedTestItem = retrievedTestGroup?.items[1]
guard let itemToRemove = retrievedTestItem else { return }
docRef.updateData([
"items" : FieldValue.arrayUnion([["title" : itemToRemove.title,
"color" : itemToRemove.color,
"number" : itemToRemove.number]])
]) { error in
if let error = error {
print("error: \(error)")
} else {
print("successfully deleted")
}
}
} catch {
}
}
}
I have printed the itemToRemove to the log to check that it is correct and it is. But it just doesn't remove it from Firestore. There is no error returned, yet the "successfully deleted" is logged.
Note the above is test code as I've simplified what I actually need just for testing purposes because I can't get this working.
Any ideas on what I'm doing wrong here?

Answer 1

You have to use arrayRemove to remove items from arrays.
#objc func removeItem() {
let docRef = FirestoreReferenceManager.simTest.document("abc")
docRef.getDocument { (document, error) in
do {
let retrievedTestGroup = try document?.data(as: TestGroup.self)
let retrievedTestItem = retrievedTestGroup?.items[1]
guard let itemToRemove = retrievedTestItem else { return }
docRef.updateData([
"items" : FieldValue.arrayRemove([["title" : itemToRemove.title,
"color" : itemToRemove.color,
"number" : itemToRemove.number]])
]) { error in
if let error = error {
print("error: \(error)")
} else {
print("successfully deleted")
}
}
} catch {
}
}
}
I've encountered situations where this straightforward approach didn't work because the item was a complex object, in which case I first had to query for the item from Firestore and plug that instance into arrayRemove() to remove it.
The reason your approach doesn't have any side effects is because arrays in Firestore are not like arrays in Swift, they are hybrids of arrays and sets. You can initialize an array in Firestore with duplicate items but you cannot append arrays using arrayUnion() with duplicate items. Trying to append a duplicate item using arrayUnion() will silently fail, such as in your case.