Android Room + Kotlin pattern - kotlin

Question

the Android Room documentation says that we should follow the singleton design pattern when instantiating an AppDatabase object.
I was thinking about it, and I would like to know if its recommended to put the AppDatabase class inside my Application class. Or if I can use the Kotlin singleton for that.
Let's say I have a DAO called CarroDAO and class CarrosDatabase that is a RoomDatabase.
Is it ok to create a DatabaseManager class using a Kotlin object/singleton ?
object DatabaseManager {
private var dbInstance: CarrosDatabase
init {
val appContext = MyApplication.getInstance().applicationContext
dbInstance = Room.databaseBuilder(
appContext,
CarrosDatabase::class.java,
"mybd.sqlite")
.build()
}
fun getCarroDAO(): CarroDAO {
return dbInstance.carroDAO()
}
}
So I can get the DAO class like this:
val dao = DatabaseManager.getCarroDAO()

Answer 1

According to Android documentation, we can create a database instance using the singleton design pattern as follows
Create a room database entity
#Entity
data class User(
#PrimaryKey var uid: Int,
#ColumnInfo(name = "first_name") var firstName: String?,
#ColumnInfo(name = "last_name") var lastName: String?
)
Create DAO class
#Dao
interface UserDao {
#Query("SELECT * FROM user")
fun getAll(): List<User>
#Query("SELECT * FROM user WHERE uid IN (:userIds)")
fun loadAllByIds(userIds: IntArray): List<User>
#Query("SELECT * FROM user WHERE first_name LIKE: first AND " +
"last_name LIKE :last LIMIT 1")
fun findByName(first: String, last: String): User
#Insert
fun insertAll(vararg users: User)
#Delete
fun delete(user: User)
}
Create database with singleton pattern
#Database(entities = arrayOf(User::class), version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
companion object {
#Volatile
private var instance: AppDatabase? = null
fun getInstance(
context: Context
): AppDatabase = instance ?: synchronized(this) {
instance ?: buildDatabase(context).also { instance = it }
}
private fun buildDatabase(context: Context): AppDatabase {
return Room.databaseBuilder(
context,
AppDatabase::class.java,
"database-name"
).build()
}
}
}
You can get database instance by following code
var databaseInstance=AppDatabase.getInstance(context)