Implementing the Room Database (Android)

Question

I like to know how to properly integrate the Room Library within an Android Application. Some articles I have seen uses a Singleton approach using a Respository for database calls, while other uses some form of Dependecy Injection (Dagger 2). I like to know the proper integration of this library?

Thanks

Answer 1

ROOM Database

• Room is an ORM (Object Relational Mapper) for SQLite database in Android developement and part of Android Jetpack.
• Provides an abstraction layer over SQLite database
• Amount of boilerplate code is reduced
• Compile-time verification of SQL queries

ROOM Database components

• It has 3 main components Entity, Database, DAO.
• Entity is data class annotated with @Entity is like creating a table in SQLite and the variables in the model class are like columns in the table.
• Database is an abstract class which extends RoomDatabase and has list of entities associated with the database.
• DAO(Data Access Object) is an interface which defines the operations to be performed in our database.

ROOM Database Implementation

• Step 1 creating Entity data class

  @Entity(tableName = "yourOwnTableName")

  data class LocalData(

    val column1: String?,
  
    val column2: String?,  
  
    @PrimaryKey(autoGenerate = true) val product_local_id: Int?= null
  

  )

• Step 2 creating Database

  @Database(entities = [LocalData::class], version = 1, exportSchema = false) @TypeConverters

  abstract class LocalDB : RoomDatabase() {

    abstract fun localDataDao() : LocalDataDAO
  
    companion object{
  
        private var instance : LocalDB ? = null
  
        fun getInstance(context: Context) : LocalDB ?{
            if(instance == null){
                synchronized(LocalDB ::class){
                    instance = Room.databaseBuilder(context.applicationContext, LocalDB::class.java, "localBD.db").allowMainThreadQueries().build()
                }
            }
            return instance
        }
  
        fun destroyInstance(){
            instance = null
        }
    }
  

  }

• Step 3 creating DAO

  @Dao interface LocalDAO {

    @Insert
    fun insertData(productEntity: LocalData) : Long
  
    @Delete
    fun deleteData(productEntity: LocalData) : Int
  
    @Query("Select * from yourOwnTableName")
    fun showAllProducts(): List<LocalData>
  
    @Query("SELECT COUNT(*) FROM yourOwnTableName")
    fun totalProducts(): Long
  

  }

• Step 4 is optional is creating repository

class ProductRepository(context: Context) {

var dbms : LocalDAO = LocalDB.getInstance(context)?.localDataDao()!!

fun insertData(productEntity: LocalData) : Long{
    return dbms.insertData(productEntity)
}

fun deleteData(productEntity: LocalData) : Int{
    return dbms.deleteData(productEntity)
}

fun getAllData() : List<LocalData> {
    return dbms.showAllProducts()
}

fun checkProductExist(id : Int) : Boolean{
    return dbms.exists(id)
}

fun totalProductsInCart() : Long{
    return dbms.totalProducts()
}

}

Answer 2

I think the best place is codelabs, it has a simple implementation, as well as a more complex one. All using Room.

Edit: Above links seems to be removed. Here are a couple of resources to replace that:

1. Android room with a view
2. Room + LiveData + ViewModel