Android Room Persistence library and Kotlin - database

Question

I am trying to write a simple app using Kotlin and Room Persistence Library.
I followed the tutorial in the Android Persistence codelab.
Here is my AppDatabase class in Kotlin:
#Database(entities = arrayOf(User::class), version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun userModel(): UserDao
companion object {
private var INSTANCE: AppDatabase? = null
#JvmStatic fun getInMemoryDatabase(context: Context): AppDatabase {
if (INSTANCE == null) {
INSTANCE = Room.inMemoryDatabaseBuilder(context.applicationContext, AppDatabase::class.java).allowMainThreadQueries().build()
}
return INSTANCE!!
}
#JvmStatic fun destroyInstance() {
INSTANCE = null
}
}
}
But when I tried to run the app, it crashes immediately.
Here is the crash log:
Caused by: java.lang.RuntimeException: cannot find implementation for com.ttp.kotlin.kotlinsample.room.AppDatabase. AppDatabase_Impl does not exist
at android.arch.persistence.room.Room.getGeneratedImplementation(Room.java:90)
at android.arch.persistence.room.RoomDatabase$Builder.build(RoomDatabase.java:340)
at com.ttp.kotlin.kotlinsample.room.AppDatabase$Companion.getInMemoryDatabase(AppDatabase.kt:19)
at com.ttp.kotlin.kotlinsample.MainKotlinActivity.onCreate(MainKotlinActivity.kt:28)
at android.app.Activity.performCreate(Activity.java:6272)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494) 
at android.app.ActivityThread.access$900(ActivityThread.java:157) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
It looks like the class AppDatabase_Impl wasn't autogenerated. I checked the original java app downloaded from codelab and found that AppDatabase_Impl was autogenerated.
Kotlin version: 1.1.2-3
Room version: 1.0.0-alpha1
Is there anyone experienced with this?
Edit:
Using kapt solves my problem. In my case, I have to replace annotationProcessor with kapt.

Answer 1

Usually in project build.gradle I define the dependencies versions:
ext {
buildToolsVersion = '25.0.2'
supportLibVersion = '25.3.1'
espressoVersion = '2.2.2'
archRoomVersion = '1.0.0-alpha1'
}
so in app build.gradle the dependencies look like:
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
compile "com.android.support:appcompat-v7:${rootProject.supportLibVersion}"
compile "android.arch.persistence.room:runtime:${rootProject.archRoomVersion}"
annotationProcessor "android.arch.persistence.room:compiler:${rootProject.archRoomVersion}"
kapt "android.arch.persistence.room:compiler:${rootProject.archRoomVersion}"
androidTestCompile("com.android.support.test.espresso:espresso-core:${rootProject.espressoVersion}", {
exclude group: 'com.android.support', module: 'support-annotations'
})
testCompile 'junit:junit:4.12'
}
Now you can define Entities Daos and Database in Kotlin.
Database:
#Database(entities = arrayOf(User::class), version = 1)
abstract class Database : RoomDatabase() {
abstract fun userDao(): UserDao
}
Entity:
#Entity(tableName = "user")
class User {
#PrimaryKey(autoGenerate = true)
var id: Int = 0
var name: String = ""
}
Dao:
#Dao
interface UserDao {
#Query("SELECT * FROM user")
fun getAll(): List<User>
#Insert
fun insertAll(vararg users: User)
#Delete
fun delete(user: User)
}
NB: Query with parameters.
Kotlin renames params, so the SQL query to retrieve all the emails that belong at a user via the userId is:
#Query("SELECT * FROM email "
+ "INNER JOIN user ON user.id = email.userId "
+ "WHERE user.id = :arg0")
fun getEmailsForUser(userId: Int): List<Email>

Answer 2

In my case, in build.gradle, when you have "annotationProcessor" you need to duplicate with "kapt" and it works.
compile "android.arch.persistence.room:runtime:$room_version"
annotationProcessor "android.arch.persistence.room:compiler:$room_version"
kapt "android.arch.persistence.room:compiler:$room_version"

Answer 3

Try out these steps
Step 1. Set the room_version in the project.gradle file
buildscript {
ext.kotlin_version = '1.1.51'
ext.room_version = '1.0.0-alpha9-1'
...
Step 2. Apply the kotlin-kapt plugin in the app.gradle file, and this solved my issue.
apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-kapt'
android {
compileSdkVersion 26
buildToolsVersion "26.0.1"
...
Step 3. Add the kapt dependency in the app.gradle file
dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation "android.arch.persistence.room:runtime:$room_version"
annotationProcessor "android.arch.persistence.room:compiler:$room_version"
kapt "android.arch.persistence.room:compiler:$room_version"
...
}

Answer 4

Anyone interested in using Kotlin with Room and Data Binding can see this sample project https://github.com/entrpn/kotlin-room-databinding

Answer 5

i almost gave up. but after doing just what dharmin007 said i also had to clean the project. that made it work. I've noticed that whenever you add kapt to gradle you MUST clean the project after synching gradle.

Answer 6

I don't know if there is a necessity to my answer I know that some of the above answers already included this to their answers but they added other things
ONLY ADD
apply plugin: 'kotlin-kapt'