IssueTracker

Component used: Room
Version used: 2.0.0
Devices/Android versions reproduced on: N/A

In current version of room if I mark method in DAO with @Transaction, and if it uses any disposable e.g. Single, the generated code will throw main thread access exception at runtime.
I would expect one of two behaviours instead:
1. It would be ideal if room could somehow defer start/end transaction to match thread that is used on Disposable, but I can imagine that this can be not possible.
2. To get compile time warning or error that this may be not the correct way of using @Transaction with mix of asynchronous code.

Example of code:
Method in abstract DAO:
   @Transaction
    open fun upsert(obj: T): Single<Boolean> {
    return insert(obj)
        .map { true }
        .onErrorResumeNext {
           if (it is SQLiteConstraintException)
                { update(obj)
                  .map { true }
            } else {
                  Single.error(it) }
            }
            .subscribeOn(Schedulers.io()) }

Generated method:

    @Override
    public Single<Boolean> upsert(Supplier obj) {
      __db.beginTransaction();
      try {
        Single<Boolean> _result = super.upsert(obj);
        __db.setTransactionSuccessful();
        return _result;
      } finally {
        __db.endTransaction();
      }
   }