为什么 Room 不创建数据库？

Question

I'm using a Room for my project but I can't create a Room Database.

Could you please, tell me what I am doing wrong?

Thanks!

I have one entity called Appointment .

@Entity
public class Appointment {
    @PrimaryKey
    @NonNull
    private final UUID uuid;
    private String title;
    private String description;

    public Appointment(UUID uuid, String title, String description) {
        this.uuid = uuid;
        this.title = title;
        this.description = description;
    }

I've implemented a DAO called AppointmentDAO :

@Dao
public interface AppointmentDAO {
    @Transaction
    @Query("SELECT * FROM Appointment")
    public List<Appointment> getAppointments();

    @Transaction
    @Query("SELECT * FROM Appointment WHERE uuid = :uuid")
    public List<Appointment> getAppointmentByUUID(UUID uuid);

    @Insert
    void insertAppointment(Appointment appointment);

    @Update
    void updateAppointment(Appointment appointment);

    @Delete
    void deleteAppointment(Appointment appointment);

    @Query("SELECT * FROM Appointment")
    Single<List<Appointment>> getAppointmentsAsyncOneShot();

    @Query("SELECT * FROM Appointment WHERE uuid = :uuid")
    Single<Appointment> getAppointmentByUUIDAsyncOneShot(UUID uuid);

    @Insert
    Completable insertAppointmentAsyncOneShot(Appointment appointment);

    @Update
    Completable updateAppointmentAsyncOneShot(Appointment appointment);

    @Delete
    Completable deleteAppointmentAsyncOneShot(Appointment appointment);

    @Query("SELECT * FROM Appointment")
    Flowable<Appointment> getAppointmentsAsyncObservable();

    @Query("SELECT * FROM Appointment WHERE uuid = :uuid")
    Flowable<Appointment> getAppointmentByUUIDAsyncObservable(UUID uuid);

}

I also created a AppDatabase abstract class:

@Database(entities = {
        Appointment.class
}, version = 1)
@TypeConverters({
        UUIDConverter.class
})
public abstract class AppDatabase extends RoomDatabase {
    private static final String TAG = "AppDatabase";

    private static final String DB_NAME = "XXXYYYYYYYYYYDatabase.db";

    private static AppDatabase instance;

    protected AppDatabase() {}

    public static synchronized AppDatabase getInstance(Context context) {
        if (instance == null) {
            instance = create(context);
        }
        return instance;
    }

    private static AppDatabase create(final Context context) {
        Log.d(TAG, "create() called with: context = [" + context + "]");
        return Room
                .databaseBuilder(context.getApplicationContext(), AppDatabase.class, DB_NAME)
                .build();
    }

    public abstract AppointmentDAO getAppointmentDAO();
}

I'm calling in a fragment this method which inserts asynchronously an Appointment :

private void addAppointmentToDatabase() {
        AppDatabase
                .getInstance(requireContext())
                .getAppointmentDAO()
                .insertAppointmentAsyncOneShot(viewModel.getAppointment().getValue())
                .subscribe(new DisposableCompletableObserver() {
                    @Override
                    public void onComplete() {
                        Toast.makeText(requireContext(), "YES", Toast.LENGTH_LONG)
                                .show();
                    }

                    @Override
                    public void onError(@NonNull Throwable e) {
                        Toast.makeText(requireContext(), "NO", Toast.LENGTH_LONG)
                                .show();
                    }
                });
    }

build.gradle (app):

plugins {
    id 'com.android.application'
}

android {
    compileSdkVersion 29
    buildToolsVersion "30.0.2"

    defaultConfig {
        applicationId "com.example.xxxxxxxx"
        minSdkVersion 22
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

        javaCompileOptions {
            annotationProcessorOptions {
                arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
            }
        }
    }

    buildFeatures {
        dataBinding true
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.2.1'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    implementation 'androidx.recyclerview:recyclerview:1.1.0'
    implementation 'com.google.android.gms:play-services-maps:17.0.0'
    implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.2.0'
    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0'
    testImplementation 'junit:junit:4.13.1'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'


    def nav_version = "2.3.2"

    // Java language implementation
    implementation "androidx.navigation:navigation-fragment:$nav_version"
    implementation "androidx.navigation:navigation-ui:$nav_version"

    // Feature module Support
    implementation "androidx.navigation:navigation-dynamic-features-fragment:$nav_version"

    // Testing Navigation
    androidTestImplementation "androidx.navigation:navigation-testing:$nav_version"

    // Jetpack Compose Integration
    implementation "androidx.navigation:navigation-compose:1.0.0-alpha04"


    implementation 'com.google.android.gms:play-services-location:17.1.0'


    def room_version = "2.2.6"

    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"

    // optional - RxJava support for Room
    implementation "androidx.room:room-rxjava2:$room_version"

    // optional - Guava support for Room, including Optional and ListenableFuture
    implementation "androidx.room:room-guava:$room_version"

    // optional - Test helpers
    testImplementation "androidx.room:room-testing:$room_version"
}

I've got no errors and no database:(.

Answer 1

Ah - you aren't properly using rxJava. Plain and simple, you can't make Database calls on the main UI thread. Room demands that they are called in a separate thread. rxJava adds a level of complexity that can make it hard to debug in the beginning. I suggest making a very simple thread with Runnable or Executors class, and call the db function inside that. Once you can confirm that your db logic is working, then you can proceed implementing rxJava.

edit: I'm not a pro at rxJava, but I do believe you are missing the function to set which thread to run on (AndroidSchedulers.io) or something like that, I can't remember off the top of my head.

Example of a Runnable:

 private void addAppointmentToDatabase(Appointment appointment) {
    new Runnable() {

        @Override
        public void run() {
            AppDatabase
                    .getInstance(requireContext())
                    .getAppointmentDAO()
                    .insertAppointment(appointment);
        }
    };
}

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