Firebase query returns wrong items

Question

Here is my database structure:

"current" : {
    "-MPcUEyEdXiotnBybJFM" : {
        "completed" : 123456789,
        "completedBy" : "Mom",
        "name" : "🍼 Babysit (2 hours)",
        "repeats" : 12,
        "startDate" : 1609144537,
        "value" : 884
    },
    "-MPcUEyF9YsmQrGpt78Q" : {
        "completed" : 1609144538,
        "completedBy" : "Mom",
        "name" : "🛠 Organize garage",
        "repeats" : 6,
        "startDate" : 1609144538,
        "value" : 884
    },
    "-MPkV1sOlx3wNS8UvEqQ" : {
        "name" : "🕸 Dust for cobwebs",
        "repeats" : 1,
        "startDate" : 1611957359,
        "value" : 221
    }
}

And here is my Firebase query:

static func deleteOldCompletedItems(completion: @escaping () -> Void) {
    
    let previousPayday = FamilyData.calculatePayday().previous.timeIntervalSince1970
    
    FB.ref
        .child(FB.jobJar)
        .child(FB.current)
        .queryOrdered(byChild: FB.completed)
        .queryEnding(atValue: previousPayday)
        .observeSingleEvent(of: .value, with: { (snapshot) in
            
            print(previousPayday)
            
            guard snapshot.exists() else {
                completion()
                return
            }

            var deletedItemsCount = 0

            for item in snapshot.children {

                guard let snap = item as? DataSnapshot else { return }

                snap.ref.removeValue { (_, _) in

                    deletedItemsCount += 1

                    if deletedItemsCount == snapshot.childrenCount {
                        completion()
                    }
                }
            }
        })
}

And here is the data model:

struct JobJar {
    var name: String
    var value: Int
    var repeats: Int
    var startDate: Double
    var completed: Double?
    var completedBy: String?
}

Note that two of the parameters are optional: completed: and completedBy:.

I want to only get the items from my database that match the completed: timestamp and that are more than a week old. Then I want to delete those items.

The code works fine for items that have a completed: parameter.

But for some reason, my query is returning items that don't have the completed: timestamp. In other words, my query is deleting the items that are more than a week old (good!) but also all the other items that don't have any timestamp. It's deleting too much stuff.

Why? Is it because the completed: parameter is optional?

How do I query the database so that I ONLY get items that have the completed: parameter that are more than a week old?

Answer 1

I'm surprised that the database returns items that don't have the property you order on. But as a workaround, you can probably add a queryStarting(atValue: 1) to the query.