How to fetch array of number in firestore using kotlin?

Question

So this is my code right now but the app still crashes when I run this:

db.collection("historyCal").document(idData.toString()).get()
    .addOnSuccessListener { document ->
        if (document != null) {
            val calin = document.get("calInDay") as List<*>
            calin.forEach {
                Log.d("someTag",calin.toString())
            }
        } else {
            Log.d("noexist", "No such document")
        }
    }

I have data that consists of:

collection: historyCal
document: id user I already put on variable idData
fields: callInDay, it's an array consist of a number (2000,2100,2000)

I want to get data from callInDay and print each value with a log:

The error log :

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.joshua.testapp, PID: 27966 kotlin.TypeCastException: null cannot be cast to non-null type kotlin.collections.List<*> at com.joshua.testapp.HistoryActivity$setBarChartValues$1.onSuccess(HistoryActivity.kt:45) at com.joshua.testapp.HistoryActivity$setBarChartValues$1.onSuccess(HistoryActivity.kt:18) at com.google.android.gms.tasks.zzn.run(Unknown Source:4) at android.os.Handler.handleCallback(Handler.java:873) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6669) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

line 45 : val calin = document.get("calInDay") as List<*> line 18 : class HistoryActivity : AppCompatActivity() { //i think this is due to line 45

Can someone help me? Thanks

no one will understand the problem without error logs. Remember to post them with all your questions. — Pemba Tamang
– Pemba Tamang, Commented Apr 15, 2021 at 7:15

Alex Mamo · Accepted Answer · 2021-04-15 08:41:42Z

1

Assuming that your POJO class is called "Calin", to get the data under "calInDay" array, please use the following lines of code:

db.collection("historyCal").document(idData.toString()).get().addOnSuccessListener { document ->
    if (document.exists()) {
        val calin = document.get("calInDay") as? List<Map<String, Calin>>
        calin.forEach {
            Log.d("someTag",calin.toString())
        }
    } else {
        Log.d("noexist", "No such document")
    }
}

So when you get the data from the "DocumentSnapshot" object, you can extract that array as a List<Map<String, Calin>>. However, if you want to map an array of objects from Cloud Firestore to a List of objects, please check the following article on Medium:

How to map an array of objects from Cloud Firestore to a List of objects?

edited Apr 15, 2021 at 8:41

answered Apr 15, 2021 at 7:20

Alex Mamo

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7 Comments

joshua Over a year ago

thanks, but i still get the same error log.. now, i change the code into this :

var calin: List<*>? = document.get("calInDay") as List<*>?                     calin?.forEach {                         Log.d("calorie",calin.toString())                     }

but i didn't get the data

Alex Mamo Over a year ago

Have you also tried val calin = document.get("calInDay") as? List<Map<String, Calin>>, as in my updated answer? Does it work this way?

joshua Over a year ago

yeah, but i still get the same error.. perhaps due to the POJO ?, internal class Calin {var cal: List<String>? = null }

Alex Mamo Over a year ago

No, that list doesn't contain String objects, it contains Calin objects. It should be: data class CalinPojo(var cal: List<Calin>? = null) and then get val cal = document.toObject(CalinPojo::class.java).cal;, as explained in that article. Does it work now?

joshua Over a year ago

oh okay i found out how to do it.. it's kinda simple just val cal = document.get("calInDay") as List<Long> dont need to make a new class.. thanks so much to help me :)

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