simplest way to apply multiple queries for firebase database in android

Question

I am wondering if it is possible to apply multiple queries for the Firebase database in Android/Kotlin.

I have a firebase database that has time value in it.

what I need to get is I want to have sales report hourly based. I get this for 1 hour but, when I try it for another hour I don't get the result. I believe I am doing something wrong here logically.

val rootRef = FirebaseDatabase.getInstance().reference
    val query1 = rootRef.child("Sales").orderByChild("time").startAt("00:00:00").endAt("00:30:00")
    val query2 = rootRef.child("Sales").orderByChild("time").startAt("23:30:00").endAt("00:00:00")

    val valueEventListener = object : ValueEventListener {
        override fun onDataChange(p0: DataSnapshot) {
            if (p0.exists()) {
                for(ds in p0.children) {
                    var timeList = arrayListOf<String>()
                    val time = ds.child("time").getValue(String::class.java)!!

                    var totalList = arrayListOf<Double>()

                    timeList.add(time)
                    println("time List : "+timeList)


                }
            }
        }

        override fun onCancelled(databaseError: DatabaseError) {
            Log.d(TAG, databaseError.getMessage()) //Don't ignore errors!
        }
    }
    query2.addListenerForSingleValueEvent(valueEventListener)
    query1.addListenerForSingleValueEvent(valueEventListener)

Can anyone help me to understand the logic here? Thanks.

......

Edited part:

Here it is what i have done: I am now saving date in miliseconds format as you suggested. And, my code looks like this :

   `val query1 = rootRef.child("Sales").orderByChild("time").startAt(1577192700000).endAt(1577192701167)
    val valueEventListener = object : ValueEventListener {
        override fun onDataChange(p0: DataSnapshot) {
            if (p0.exists()) {
                for(ds in p0.children) {

                    var timeList = arrayListOf<Long>()
                    val time = ds.child("time").getValue(Long::class.java)!!


                   // var totalList = arrayListOf<Double>()

                    timeList.add(time)
                    println("time List : "+timeList)


                }
            }
        }`

when I use miliseconds (long value) as startAt() paramater it gives me error.

score 0 · Answer 1 · answered Dec 24 '19 at 12:35

0

I get this for 1 hour but, when I try it for another hour I don't get the result.

The problem in your code is that you are passing strings to the startAt() and endAt() methods. Strings are ordered lexicographically, meaning that the following query:

val query1 = rootRef.child("Sales").orderByChild("time").startAt("00:00:00").endAt("00:30:00")

Will work since 00:30:00 is after 00:00:00 but the second query:

val query2 = rootRef.child("Sales").orderByChild("time").startAt("23:30:00").endAt("00:00:00")

Will not return any results. To solve this, you should store the time as a timestamp and not as a String. To achieve this, please see my answer from the following post:

How to save the current date/time when I add new value to Firebase Realtime Database

In the end, just pass timestamps (long values) to both startAt() and endAt() methods and your problem will be solved.

answered Dec 24 '19 at 12:35

Alex Mamo

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Thanks @alexmamo, i will check soon and let you know the result. – David Green Dec 24 '19 at 12:36
Ok, keep me posted ;) – Alex Mamo Dec 24 '19 at 12:37
I have edited my code there you can find an error I see. Sorry, I couldn't post here as it is too long. – David Green Dec 24 '19 at 17:24
As I said in my answer, you should pass a long, not a string or a boolean, right? – Alex Mamo Dec 24 '19 at 18:02
but, isn't that what I am not passing? `startAt(1577192700000)` – David Green Dec 25 '19 at 01:23
The easiest fix for your code is to use `val` instead of `var`. Does it work this way? – Alex Mamo Dec 25 '19 at 08:04

simplest way to apply multiple queries for firebase database in android

1 Answers1