Using room as singleton in kotlin

Question

I\'m trying to use Room as singleton so I didn\'t have to invoke Room.databaseBuilder() -which is expensive- more than once.

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Answer 1

You could make use of the Kotlin standard library's

fun  lazy(LazyThreadSafetyMode.SYNCHRONIZED, initializer: () -> T): Lazy

companion object {
    private lateinit var context: Context
    private val database: AppDatabase by lazy(LazyThreadSafetyMode.SYNCHRONIZED) {
        Room.databaseBuilder(context, AppDatabase::class.java, "trains.db").build()
    }
    fun getDatabase(context: Context): AppDatabase {
        this.context = context.applicationContext
        return database
    }
}

Personally though, I would normally add ApplicationContext-dependent singletons inside the Application, e.g.

  
...

class MyApplication : Application() {
    val database: AppDatabase by lazy {
        Room.databaseBuilder(this, AppDatabase::class.java, "train.db").build()
    }
}

You can even define an extension method for easy access as context.database.

val Context.database
    get() =
        generateSequence(applicationContext) {
       (it as? ContextWrapper)?.baseContext
       }.filterIsInstance().first().database