Room query returning Maybe<List> crashes app when returns empty result

Question

I have a room query:

@Query("SELECT * FROM classes WHERE _id IN(:values) ORDER BY date DESC")
fun getClassesByIds(values: List<Int>): Maybe<List<YClass>>

---

compositeDisposable.add(viewModel.getClassesById(classesTaken)
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .doOnSuccess { list ->
                        list.forEach {

                            setupInfo(student)
                        }
                    }
                    .doOnError { it.printStackTrace() }
                    .subscribe())

When the result is empty app crashes when I navigate back from the activity. Actually crash happens when another query is being executed. THat second query is erroring even though there's nothing wrong with it.

Caused by: android.arch.persistence.room.EmptyResultSetException: Query returned empty result set: SELECT * FROM classes WHERE _id IN() ORDER BY date DESC

03-06 00:07:53.476 31132-31199/? I/InputDispatcher: Window 'Window{135734f u0 com.labfoodandfriends.nikitagudkovs.jlog/com.labfoodandfriends.nikitagudkovs.jlog.activity.student_and_teacher.StudentOverview}' spent 4249.1ms processing the last input event: KeyEvent(deviceId=-1, source=0x00000101, action=1, flags=0x00000048, keyCode=4, scanCode=0, metaState=0x00000000, repeatCount=0), policyFlags=0x6b000002 03-06 00:07:53.612 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64: Compiler allocated 6MB to compile void android.view.ViewRootImpl.performTraversals() 03-06 00:07:53.661 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64: Do full code cache collection, code=502KB, data=339KB 03-06 00:07:53.662 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64: After code cache collection, code=501KB, data=295KB 03-06 00:07:55.873 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err: io.reactivex.exceptions.OnErrorNotImplementedException: Query returned empty result set: SELECT * FROM classes WHERE _id IN() ORDER BY date DESC 03-06 00:07:55.874 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:704) 03-06 00:07:55.875 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:701) 03-06 00:07:55.875 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.observers.ConsumerSingleObserver.onError(ConsumerSingleObserver.java:47) 03-06 00:07:55.876 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.operators.single.SingleDoOnError$DoOnError.onError(SingleDoOnError.java:63) 03-06 00:07:55.876 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.operators.single.SingleDoOnSuccess$DoOnSuccess.onError(SingleDoOnSuccess.java:64) 03-06 00:07:55.877 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.operators.single.SingleObserveOn$ObserveOnSingleObserver.run(SingleObserveOn.java:79) 03-06 00:07:55.877 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:109) 03-06 00:07:55.878 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at android.os.Handler.handleCallback(Handler.java:790) 03-06 00:07:55.878 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err: at android.os.Handler.dispatchMessage(Handler.java:99) 03-06 00:07:55.878 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at android.os.Looper.loop(Looper.java:164) 03-06 00:07:55.879 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at android.app.ActivityThread.main(ActivityThread.java:6494) 03-06 00:07:55.879 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err: at java.lang.reflect.Method.invoke(Native Method) 03-06 00:07:55.879 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 03-06 00:07:55.880 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 03-06 00:07:55.881 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err: Caused by: android.arch.persistence.room.EmptyResultSetException: Query returned empty result set: SELECT * FROM classes WHERE _id IN() ORDER BY date DESC 03-06 00:07:55.881 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at com.labfoodandfriends.nikitagudkovs.jlog.database.dao.StudentDAO_Impl$6.call(StudentDAO_Impl.java:345) 03-06 00:07:55.882 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at com.labfoodandfriends.nikitagudkovs.jlog.database.dao.StudentDAO_Impl$6.call(StudentDAO_Impl.java:327) 03-06 00:07:55.882 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.operators.single.SingleFromCallable.subscribeActual(SingleFromCallable.java:44) 03-06 00:07:55.883 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.Single.subscribe(Single.java:3096) 03-06 00:07:55.883 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.operators.single.SingleSubscribeOn$SubscribeOnObserver.run(SingleSubscribeOn.java:89) 03-06 00:07:55.884 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:463) 03-06 00:07:55.884 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err: at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:66) 03-06 00:07:55.885 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:57) 03-06 00:07:55.885 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at java.util.concurrent.FutureTask.run(FutureTask.java:266) 03-06 00:07:55.885 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err: at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:301) 03-06 00:07:55.886 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162) 03-06 00:07:55.886 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636) 03-06 00:07:55.887 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at java.lang.Thread.run(Thread.java:764) 03-06 00:07:55.903 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64: Do partial code cache collection, code=503KB, data=301KB 03-06 00:07:55.904 31132-15809/? W/ActivityManager: Force finishing activity com.labfoodandfriends.nikitagudkovs.jlog/.activity.students.StudentsActivity 03-06 00:07:55.909 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64: After code cache collection, code=503KB, data=301KB 03-06 00:07:55.909 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64: Increasing code cache capacity to 2MB 03-06 00:07:55.920 31132-31147/? I/ActivityManager: Showing crash dialog for package com.labfoodandfriends.nikitagudkovs.jlog u0 03-06 00:07:55.990 31132-1471/? I/OpenGLRenderer: Initialized EGL, version 1.4 03-06 00:07:55.990 31132-1471/? D/OpenGLRenderer: Swap behavior 2 03-06 00:07:56.407 31132-31146/? W/ActivityManager: Activity pause timeout for ActivityRecord{395d736 u0 com.labfoodandfriends.nikitagudkovs.jlog/.activity.students.StudentsActivity t7082 f}

Antonetta

You might want to post the entire Java stack trace. – Teressaterete

@Teressaterete updated – Antonetta

Did you try changing the return type from Maybe<List<YClass>> to Single<List<YClass>>? Given that you are expecting a List, you don't really need to make it Maybe, as it should return the expected empty list with a Single. (if that works, we can figure out why Maybe doesn't work) – Sileas

@Sileas Single and Maybe work the same way here. I changed it to Flowable, which fixed my issue but is not an optimal choice as I only make this request once. – Antonetta

Answer 1

as @insa_c mentioned, this is the expected behavior. what you can do is to check for the EmptyResultSetException and return the empty container instead.

    compositeDisposable.add(viewModel.getClassesById(classesTaken)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .doOnSuccess { list ->
                    list.forEach { 
                        setupInfo(student)
                    }
                }

           //You add this to return an empty set when an error occurs
            .onErrorResumeNext(error -> {
                if (error instanceof EmptyResultSetException) 
                     return Single.just(new ArrayList<>()); //<< an empty container is returned.
                else 
                     return Single.error(error);
            });                    

            //the rest of your stuffs.
                .doOnError { it.printStackTrace() } 
                .subscribe())

Monarchy

Answer 2

For people who might be interested in this issue:

As explained in this post Room with Single explained

if you use a Maybe or a Single as return type from an query, it'll call subscriber.onError(new EmptyResultSetException()) when the result from the query is empty. So that's completely working as expected.

Dendrite

Maybe never call EmptyResultSetException(), just returns no rows and complate – Ediva