当返回空结果时，房间查询返回 Maybe<List> 使应用程序崩溃

Question

我有一个房间查询：

@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())

当我从活动导航回来时，结果为空应用程序崩溃。实际上崩溃是在执行另一个查询时发生的。即使没有任何问题，第二个查询也会出错。

引起：android.arch.persistence.room.EmptyResultSetException：查询返回空结果集：SELECT * FROM classes WHERE _id IN() ORDER BY date DESC

03-06 00:07:53.476 31132-31199/? I/InputDispatcher: 窗口 'Window{135734f u0 com.labfoodandfriends.nikitagudkovs.jlog/com.labfoodandfriends.nikitagudkovs.jlog.activity.student_and_teacher.StudentOverview}' 花了 4249.1ms 处理最后一个输入事件：KeyEvent(deviceId) =0x00000101，动作=1，标志=0x00000048，keyCode=4，scanCode=0，metaState=0x00000000，repeatCount=0），policyFlags=0x6b000002 03-06 00:07:53.612/1373.612-137d I/zygote64：编译器分配了 6MB 来编译 void android.view.ViewRootImpl.performTraversals() 03-06 00:07:53.661 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64：代码=全码缓存集合502KB, data=339KB 03-06 00:07:53.662 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64：代码缓存收集后，
在 io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:704) 03-06 00:07:55.875 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/
System.reerr .internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:701) 03-06 00:07:55.875 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.erractive:
at io.reactive .ConsumerSingleObserver.onError(ConsumerSingleObserver.java:47) 03-06 00:07:55.876 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
at io.reactivex.onsingOnleError$Error .onError(SingleDoOnError.java:63) 03-06 00:07:55.876 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：
在 io.reactivex.internal.operators.single.SingleDoOnSuccess$DoOnSuccess.onError(SingleDoOnSuccess.java:64) 03-06 00:07:55.877 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog 在 W/
io. .reactivex.internal.operators.single.SingleObserveOn$ObserveOnSingleObserver.run(SingleObserveOn.java:79) 03-06 00:07:55.877 13731-13731/com.labfoodandfriends.nikitagudkovs.errjlogactive/
System.re .android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:109) 03-06 00:07:55.878 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：
在 android.os.Handler.handleCallback(Handler.java:790) 03-06 00:07:55.878 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：在 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/com.1373friends .nikitagudkovs.jlog W/System.err: 在 java.lang.reflect.Method.invoke(Native Method) 03-06 00:07:55.879 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
在 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：
在 com.android .internal.os.ZygoteInit.main(ZygoteInit.java:807) 03-06 00:07:55.881 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：由：android.arch.persistence.room .EmptyResultSetException：查询返回空结果集：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：
在 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.errlog/W
在 com.labfoodandfriends.nikitagudkovs.jlog.database.dao.StudentDAO_Impl$6.call(StudentDAO_Impl.java:327) 03-06 00:07:55.882 13731-13731/com.labfoodandfriends.nikjerrr/
at io.reactivex.internal.operators.single.SingleFromCallable.subscribeActual(SingleFromCallable.java:44) 03-06 00:07:55.883 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.errx:
at Single.subscribe(Single.java:3096) 03-06 00:07:55.883 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：
在 io.reactivex.internal.operators.single.SingleSubscribeserverOn$SubscribeOnOb运行（SingleSubscribeOn.java:89）03-06 00:07:55.884 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：
在 io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:463) 03-06 00:07:55.884 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：在 io.reactivex.internal.schedul .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.ScheduledRunableRunnable(ScheduledRunnable.Scheduled) .java:57) 03-06 00:07:55.885 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：
在 java.util.concurrent.FutureTask.run(FutureTask.java:266) 03-06 00:07:55.885 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：在 java.util.concurrent.ScheduledThreadPoolExecutor $ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:301) 03-06 00:07:55.886 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：
在 java.util.concurrent.ThreadPoolExecutor.javaWorker. :1162) 03-06 00:07:55.886 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err:
在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:6306) 03 00:07:55.887 13731-13731/com.labfoodandfriends.nikitagudkovs.jlog W/System.err：
在 java.lang.Thread.run(Thread.java:764) 03-06 00:07:55.903 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64：做部分代码缓存收集，代码=503KB，数据= 301KB 03-06 00:07:55.904 31132-15809/? W/ActivityManager：强制完成活动 com.labfoodandfriends.nikitagudkovs.jlog/.activity.students.StudentsActivity 03-06 00:07:55.909 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64 代码缓存集后： =503KB，数据=301KB 03-06 00:07:55.909 13731-13736/com.labfoodandfriends.nikitagudkovs.jlog I/zygote64：将代码缓存容量增加到 2MB 03-06 00:07:5111422/3736/com.labfoodandfriends.nikitagudkovs.jlog I/ActivityManager：显示包 com.labfoodandfriends.nikitagudkovs.jlog u0 03-06 00:07:55.990 31132-1471/? I/OpenGLRenderer：初始化 EGL，版本 1.4 03-06 00:07:55。990 31132-1471/? D/OpenGLRenderer：交换行为 2 03-06 00:07:56.407 31132-31146/? W/ActivityManager：ActivityRecord 的活动暂停超时{395d736 u0 com.labfoodandfriends.nikitagudkovs.jlog/.activity.students.StudentsActivity t7082 f}

Answer 1

正如@insa_c 提到的，这是预期的行为。您可以做的是检查 EmptyResultSetException 并返回空容器。

    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())

Answer 2

对于可能对这个问题感兴趣的人：

正如这篇文章中所解释的，单人房解释

如果您使用 aMaybe或 aSingle作为查询的返回类型，它将subscriber.onError(new EmptyResultSetException())在查询结果为空时调用。所以这完全按预期工作。