How to query items with timestamps on Firebase?

Question

I want to query active items from a Firebase node. An active item is delimited by a start date and an end.
Here is a sample of the structure :

{
    "items" : {
        "itme1" : {
            "data" : "...", //some data
            "startDate" : 12345678,
            "endDate" : 23456789
        },
        "item2" : {...}
    }
}

Dates are Firebase timestamps to prevent user time shifting.
An item is saved on Firebase server like this:

//Init data to save
var dictionary = Dictionary<String,Any>()
dictionary["data"] = "some data"
dictionary["startDate"] = FIRServerValue.timestamp()

//Save data on Firebase
let itemRef = FIRDatabase.database().reference(withPath: "items").childByAutoId()
itemRef.setValue(dictionary)

//Set end date
itemRef.observeSingleEvent(of: FIRDataEventType.value, with: { (snapshot) in
    if let dict = snapshot.value as? NSDictionary, let createdAt = dict["startDate"] as? TimeInterval {
        let startDate = Date(firebaseTimestamp: createdAt)
        let endDate = startDate.dateByAddingHours(1) //Add one hour to startDate
        itemRef.updateChildValues(["endDate":endDate.timeIntervalSince1970 * 1000])
    }
})

How can I query Firebase to get items where endDate >= FIRServerValue.timestamp() (active items) ?

As firebase timestamp FIRServerValue.timestamp() can only be known only after it has been written on Firebase, I cannot query FIRServerValue.timestamp() directly. Maybe there is a better way to set endDate. How do people handle this?

Any reason you can't query on endDate startingAtValue(currentTimeStamp)? That will return all nodes where the endDate is greater than the currentTime. Maybe I don't fully understand the question? Do you always want to write the current time stamp as the start date and the end date will always be one hour later? — Jay, Oct 26 '16 at 18:25
I can query `endDate startingAtValue(currentTimeStamp)` but to get currentTimeStamp I need to save `FIRServerValue.timestamp()` a first time on firebase to get the current value. It would be a resources-consuming query so maybe there is another solution to deal with timestamps. — Bogy, Oct 27 '16 at 11:53
And yes I always want to save the current times tamp as the start date and the end date can vary (1 hour or more). — Bogy, Oct 27 '16 at 11:55

score 1 · Answer 1 · answered Oct 26 '16 at 18:32

1

You could try something like this. This would only query items where the end date equals the current date or greater.

let removeBeforeThisDate = NSDate()
let currentDateTimestamp = removeBeforeThisDate.timeIntervalSince1970

itemRef.queryOrderedByChild("endDate").queryStartingAtValue(currentDateTimestamp).observeEventType(.Value, withBlock: { snapshot in
...

answered Oct 26 '16 at 18:32

chickenparm

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I agree but the timestamp can be easily modified by the user if he changes the time of his device. – Bogy Oct 27 '16 at 12:01
You can use let serverTime = ServerValue.timestamp() which you can pass as a value to a query. The server will interpret this as the current time stamp when it is received. Look here for more information: https://stackoverflow.com/questions/25536547/how-do-i-get-a-server-timestamp-from-firebases-ios-api – DoesData Jan 04 '18 at 13:47

How to query items with timestamps on Firebase?

1 Answers1