Room multimap LEFT JOIN nullability [201946438]

Fixed

Bug

Status Update

No update yet.

Description

aa...@gmail.com

created issue #1

Oct 4, 2021 02:36PM

Artifact used : Room Version used: 2.4.0-alpha05 Devices/Android versions reproduced on: Emulator

This is more of a feature request, but trying out the new multimap feature I'm having issues with LEFT JOIN queries.

Take this example from the release notes (One-to-Many relationship):

@Query("SELECT * FROM Artist JOIN Album ON Artist.id = Album.artistId")
fun getArtistAndAlbums(): Map<Artist, List<Album>>

Let's say we want all artists, regardless if they have any albums. So we change the query to use a LEFT JOIN:

@Query("SELECT * FROM Artist LEFT JOIN Album ON Artist.id = Album.artistId")
fun getArtistAndAlbums(): Map<Artist, List<Album>>

This won't work if we have an Artist without albums, if Album doesn't have any nullable fields. Because the current implementation will always try and generate an Album object.

Is it possible to let Room return an empty list of 'Albums' in that case? Or Map<Artist, List<Album>?>?

Thanks for your time!

Comments

au...@google.com <au...@google.com> Oct 6, 2021 08:29PM

Assigned to da...@google.com.

el...@google.com <el...@google.com> #2Oct 6, 2021 09:42PM

Reassigned to el...@google.com.

For one of observables (single, maybe) we don't specify a subscvription thread so that developer can control where the action happens.
For flowables / observables; we always use the Room IO thread fo rthe actual query since we may repeat the work.

For LiveData, ti si always the Room IO Thread.

Until we can extend Room Query methods to receive non-query parameter (e.g. a Scheduler) we cannot do this.
At least room catches this instantly since it will crash w/ db access on main thread exception.

aa...@gmail.com <aa...@gmail.com> #3Oct 11, 2021 10:56AM

Hello Yigit, nice to meet you here! :)
Probably I should have described the problem more clearly.

I'm using Flowable, and hopefully it executes queries in background thread (at least, app does not crash with IllegalStateException, as with Single).

But nevertheless subscribing and disposing(!) does cause StrictMode violations. Stack trace examples:

D/StrictMode: StrictMode policy violation; ~duration=17 ms: android.os.StrictMode$StrictModeDiskWriteViolation: policy=31 violation=1
at android.os.StrictMode$AndroidBlockGuardPolicy.onWriteToDisk(StrictMode.java:1111)
at android.database.sqlite.SQLiteConnection.applyBlockGuardPolicy(SQLiteConnection.java:1043)
at android.database.sqlite.SQLiteConnection.execute(SQLiteConnection.java:552)
at android.database.sqlite.SQLiteSession.beginTransactionUnchecked(SQLiteSession.java:323)
at android.database.sqlite.SQLiteSession.beginTransaction(SQLiteSession.java:298)
at android.database.sqlite.SQLiteDatabase.beginTransaction(SQLiteDatabase.java:505)
at android.database.sqlite.SQLiteDatabase.beginTransaction(SQLiteDatabase.java:416)
at androidx.sqlite.db.framework.FrameworkSQLiteDatabase.beginTransaction(FrameworkSQLiteDatabase.java:69)
at androidx.room.InvalidationTracker.syncTriggers(InvalidationTracker.java:426)
at androidx.room.InvalidationTracker.syncTriggers(InvalidationTracker.java:465)
at androidx.room.InvalidationTracker.addObserver(InvalidationTracker.java:249)
at androidx.room.RxRoom$1.subscribe(RxRoom.java:79)
at io.reactivex.internal.operators.flowable.FlowableCreate.subscribeActual(FlowableCreate.java:71)
at io.reactivex.Flowable.subscribe(Flowable.java:14479)
at io.reactivex.internal.operators.flowable.FlowableObserveOn.subscribeActual(FlowableObserveOn.java:56)
at io.reactivex.Flowable.subscribe(Flowable.java:14479)
at io.reactivex.internal.operators.flowable.FlowableFlatMapMaybe.subscribeActual(FlowableFlatMapMaybe.java:54)
at io.reactivex.Flowable.subscribe(Flowable.java:14479)
at io.reactivex.Flowable.subscribe(Flowable.java:14416)
at io.reactivex.Flowable.subscribe(Flowable.java:14306)
at gmk57.strictroom.MainActivity.onCreate(MainActivity.java:30)

StrictMode policy violation; ~duration=108 ms: android.os.StrictMode$StrictModeDiskWriteViolation: policy=31 violation=1
at android.os.StrictMode$AndroidBlockGuardPolicy.onWriteToDisk(StrictMode.java:1111)
at android.database.sqlite.SQLiteConnection.applyBlockGuardPolicy(SQLiteConnection.java:1043)
at android.database.sqlite.SQLiteConnection.execute(SQLiteConnection.java:552)
at android.database.sqlite.SQLiteSession.beginTransactionUnchecked(SQLiteSession.java:323)
at android.database.sqlite.SQLiteSession.beginTransaction(SQLiteSession.java:298)
at android.database.sqlite.SQLiteDatabase.beginTransaction(SQLiteDatabase.java:505)
at android.database.sqlite.SQLiteDatabase.beginTransaction(SQLiteDatabase.java:416)
at androidx.sqlite.db.framework.FrameworkSQLiteDatabase.beginTransaction(FrameworkSQLiteDatabase.java:69)
at androidx.room.InvalidationTracker.syncTriggers(InvalidationTracker.java:426)
at androidx.room.InvalidationTracker.syncTriggers(InvalidationTracker.java:465)
at androidx.room.InvalidationTracker.removeObserver(InvalidationTracker.java:281)
at androidx.room.RxRoom$1$2.run(RxRoom.java:83)
at io.reactivex.disposables.ActionDisposable.onDisposed(ActionDisposable.java:30)
at io.reactivex.disposables.ActionDisposable.onDisposed(ActionDisposable.java:19)
at io.reactivex.disposables.ReferenceDisposable.dispose(ReferenceDisposable.java:43)
at io.reactivex.internal.disposables.DisposableHelper.dispose(DisposableHelper.java:124)
at io.reactivex.internal.disposables.SequentialDisposable.dispose(SequentialDisposable.java:72)
at io.reactivex.internal.operators.flowable.FlowableCreate$BaseEmitter.cancel(FlowableCreate.java:301)
at io.reactivex.internal.operators.flowable.FlowableObserveOn$BaseObserveOnSubscriber.cancel(FlowableObserveOn.java:154)
at io.reactivex.internal.operators.flowable.FlowableFlatMapMaybe$FlatMapMaybeSubscriber.cancel(FlowableFlatMapMaybe.java:158)
at io.reactivex.internal.subscriptions.SubscriptionHelper.cancel(SubscriptionHelper.java:189)
at io.reactivex.internal.subscribers.LambdaSubscriber.cancel(LambdaSubscriber.java:119)
at io.reactivex.internal.subscribers.LambdaSubscriber.dispose(LambdaSubscriber.java:104)
at gmk57.strictroom.MainActivity.onDestroy(MainActivity.java:37)

el...@google.com <el...@google.com> Nov 4, 2021 12:12AM

Marked as fixed.

ap...@google.com <ap...@google.com> #4Nov 4, 2021 12:13AM

oh this is bad :/ we should fix it, thanks!

mr...@crossway.org <mr...@crossway.org> #5Dec 2, 2021 08:50PM

Looks like it is broken for both add observer and remove observer since both are sync.
We need to investigate this better because these methods were not @WorkerThread before and we had to change them to fix some invalidation problems (see internal bug

b/73592149

).
Luckily this is not an issue for LiveData since it uses ComputableLiveData and always calls observe on a background thread.

mr...@crossway.org <mr...@crossway.org> #6Dec 2, 2021 09:51PM

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 79deed62f2188a6ce2d21244dd28c3dc8ab6d0de
Author: Daniel Santiago Rivera <danysantiago@google.com>
Date: Wed Oct 17 11:07:39 2018

Specify subscribeOn and unsubscribeOn scheduler in RxRoom.

Setting subscriber and unsubscriber schedulers prevents triggers being
synced in the main thread when subscribing or disposing a RxRoom
flowable / observable.

Moved beginTransaction() calls in InvalidationTracker outside the try,
finally with endTransaction() so that exceptions thrown by
beginTransaction() aren't aborted nor forgotten.

Bug: 117201279
Test: Manual test with sample app.
Change-Id: Iefb33dc63cf78e125a8805bd66a26ada365d8453

A room/integration-tests/testapp/src/androidTest/java/androidx/room/integration/testapp/test/InvalidationTrackerTest.java
M room/runtime/src/main/java/androidx/room/InvalidationTracker.java
M room/rxjava2/src/main/java/androidx/room/RxRoom.java
M room/rxjava2/src/test/java/androidx/room/RxRoomTest.java

https://android-review.googlesource.com/792524

https://goto.google.com/android-sha1/79deed62f2188a6ce2d21244dd28c3dc8ab6d0de