Android Room Persistence library and Kotlin

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>