How to handel no results with Android Room and RxJava 2?

Question

I have database with table contact and I want to check if there is contact with some phone number.

@Query("SELECT * FROM contact WHERE phone_number = :number")
Flowable findByPhoneNumber(int number);

I have RxJava 2 Composite disposable with statement from above to check if there is contact with phone number.

disposable.add(Db.with(context).getContactsDao().findByPhoneNumber(phoneNumber)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribeWith(new DisposableSubscriber() {
                @Override
                public void onNext(final Contact contact) {
                    Log.d("TAG", "phone number fined");
                    Conversation conversation;
                    if(contact != null){
                        conversation = Db.with(context).getConversationsDao().findBySender(contact.getContactId());
                        if(conversation != null){
                            conversation.setUpdatedAt(Utils.getDateAndTimeNow());
                            saveConversation(contact, conversation, context, text, phoneNumber, false);
                        } else {
                            conversation = getConversation(contact, contact.getPhoneNumber());
                            saveConversation(contact, conversation, context, text, phoneNumber, true);
                        }
                    } else {
                        conversation = Db.with(context).getConversationsDao().findByPhone(phoneNumber);
                        if(conversation != null){
                            conversation.setUpdatedAt(Utils.getDateAndTimeNow());
                            saveConversation(contact, conversation, context, text, phoneNumber, false);
                        } else {
                            conversation = getConversation(contact, phoneNumber);
                            saveConversation(contact, conversation, context, text, phoneNumber, true);
                        }
                    }
                }

                @Override
                public void onError(Throwable t) {
                    Log.d("TAG", "find phone number throwable");
                    Toast.makeText(context, t.getLocalizedMessage(), Toast.LENGTH_LONG).show();
                }

                @Override
                public void onComplete() {
                    Log.d("TAG", "onComplete");
                }
            }));

This is working fine if query can find contact with required phone number, but if there is result, it nothing happens.

Here are two test cases that I wrote and they work fine:

@RunWith(AndroidJUnit4.class)
public class ContactsTest {

    private AppDatabase db;

    @Rule
    public InstantTaskExecutorRule instantTaskExecutorRule =
            new InstantTaskExecutorRule();

    @Before
    public void initDb() throws Exception {
        db = Room.inMemoryDatabaseBuilder(
                InstrumentationRegistry.getContext(),
                AppDatabase.class)
                // allowing main thread queries, just for testing
                .allowMainThreadQueries()
                .build();
    }

    @After
    public void close(){
        db.close();
    }

    @Test
    public void insertAndFindTest(){
        final Contact contact = new Contact();
        contact.setName("Test");
        contact.setPhoneNumber(555);
        db.contactsDao()
                .insert(contact);

        db.contactsDao().findByPhoneNumber(contact.getPhoneNumber())
                .test()
                .assertValue(new Predicate() {
                    @Override
                    public boolean test(@NonNull Contact savedContact) throws Exception {
                        if(savedContact.getPhoneNumber() == contact.getPhoneNumber()){
                            return true;
                        }
                        return false;
                    }
                });
    }

    @Test
    public void findNoValues(){
        db.contactsDao().findByPhoneNumber(333)
                .test()
                .assertNoValues();
    }

}

How I can solve this?

user_2471275 · Answer

I guess you also could use wrapper with Single. Like:

public class QueryResult {
            public D data;
            public QueryResult() {}

            public QueryResult(D data) {
                this.data = data;
            }

            public boolean isEmpty(){
                return data != null;
            }
 }

And use it like:

public Single> getTransaction(long id) {
            return createSingle(() -> database.getTransactionDao().getTransaction(id))
                    .map(QueryResult::new);
}

Where createAsyncSingle:

protected  Single createSingle(final Callable func) {
            return Single.create(emitter -> {
                try {
                    T result = func.call();
                    emitter.onSuccess(result);

                } catch (Exception ex) {
                    Log.e("TAG", "Error of operation with db");
                }
            });
}

Don't forget to use IO thread.

How to handel no results with Android Room and RxJava 2?

4 Answers