Firestore Swift：通过更新数据添加多个子地图

Question

I've come across a scenario where I want something structured like this:

I tried to do set the data by doing

var mapValues: [String : Any] {
            return [ user_uuid! :
                        [
                            "name" : AuthViewModel().decodeUserInfo()?.displayName! as Any,
                            "checkInTime" : "",
                            "checkOutTime" : "",
                        ]
            ]
        }
            
db.collection("Collection")
     .document(eventID).updateData(["attendees" : mapValues])

However, the problem with this is that it does not "append" a new child to the map. Instead, I am overriding it. Is there a way to add a new "element" without wiping everything else? I am looking for something that works similar to FieldValue.arrayUnion , but without changing my structure to an array.

Answer 1

When you call updateData the database writes only the fields that you specify, but for those fields any existing value in the database is indeed replaced.

If you want to add an item to the array and all your items are unique, you can use the array-union operator .

Note that it is never possible to update a value in an array item, so if you want to say update the name for an existing item, you will have to:

1. Read the array from the document.
2. Update the array in your application code.
3. Write the entire array field back to the database.