离线时，Firebase值事件不会一直触发

Question

I have the following path pattern:

/ID_Company/boxes/timestamp_of_the_day/ID_box

Let's say I just started a new day and I'm offline. Right now on Firebase DB, the path /ID_Company/boxes/timestamp_of_TODAY doesn't exist, neither in the cache.

No I add a new box to the path /ID_Company/boxes/timestamp_of_TODAY/id_box1

If I have an observer on childAdded event, it will be triggered. But if I have an observer on value event, nothing is triggered.

Now let say that I was online when I added the first box. So on firebase this path /ID_Company/boxes/timestamp_of_TODAY/id_box1 exists and so it does locally.

It go offline. And I add a new box on /ID_Company/boxes/timestamp_of_TODAY/id_box2 , then 'value` event is triggered and I just don't understand why.

Why is it triggered when timestamp_of_TODAY already exists but not when it doesn't?

Thanks for your help.

EDIT:

Here is how I add a box:

        guard let startingTimestamp = date.beginning(of: .day)?.timeIntervalSince1970 else { return nil }

        let boxRef = dbRef.child("ID_Company").child("boxes").child("\(startingTimestamp)").childByAutoId()

        var box = box
        box.id = boxRef.key

        boxRef.setValue(box.toDictionary()) { error, ref in
            if let error = error as? NSError {
                print(error)
                completion(error)
            } else {
                completion(nil)
            }
        }

And here is how I get boxes:

    guard let startingTimestamp = day.beginning(of: .day)?.timeIntervalSince1970, let endingTimestamp = day.end(of: .day)?.timeIntervalSince1970 else { return nil }

    let boxesRef = dbRef.child("ID_Company").child("boxes").child("\(startingTimestamp)")

    let query = boxesRef.queryOrdered(byChild: Box.Key.dateTimestamp.rawValue).queryStarting(atValue: startingTimestamp).queryEnding(atValue: endingTimestamp + 0.001)

    let handle = query.observe(.value, with: { snapshot in
        var boxes: [Box] = []

        for child in snapshot.children {
            let box = Box(snapshot: child as! FIRDataSnapshot)

            if userID == nil || box.userID == userID! {
                boxes.append(box)
            }
        }

        completion(boxes.reversed())
    })

Answer 1

I am sure but please try below. Might be work for you.

guard let startingTimestamp = day.beginning(of: .day)?.timeIntervalSince1970, let endingTimestamp = day.end(of: .day)?.timeIntervalSince1970 else { return nil }

let boxesRef = dbRef.child("ID_Company").child("boxes").child("\(startingTimestamp)")

let query = boxesRef.queryOrdered(byChild: Box.Key.dateTimestamp.rawValue).queryStarting(atValue: startingTimestamp).queryEnding(atValue: endingTimestamp + 0.001)

let handle = query.observe(.ChildAdded, with: { snapshot in
    var boxes: [Box] = []

    for child in snapshot.children {
        let box = Box(snapshot: child as! FIRDataSnapshot)

        if userID == nil || box.userID == userID! {
            boxes.append(box)
        }
    }

    completion(boxes.reversed())
})

Answer 2

Look at this document: FIRDataEventTypeValue

You can use the FIRDataEventTypeValue event to read the data at a given path, as it exists at the time of the event

Hope it can help you.