https://developer.android.com/training/data-storage/room#setup
def roomVersion = "2.4.0"
implementation("androidx.room:room-runtime:$roomVersion")
annotationProcessor("androidx.room:room-compiler:$roomVersion")
// To use Kotlin annotation processing tool (kapt)
kapt("androidx.room:room-compiler:$roomVersion")
// optional - Kotlin Extensions and Coroutines support for Room
implementation("androidx.room:room-ktx:$roomVersion")
Also needs kotlin-kapt plugin.
plugins {
...
id "kotlin-kapt"
}
// Entity
// ===================================================================================
// Entity defines table inside the database.
// An entity data class can be used to refer
// to individual entries (row) in the table.
// This is similar to model class.
@Entity(tableName = "Table1")
data class Table1Entity (
@PrimaryKey(autoGenerate = true)
val id: Int,
val name: String
)
// ===================================================================================
// DAO
// ===================================================================================
// DAO - Data Access Objects
// This is not an object though.
// DAO is an interface,
// having methods for operations on table.
// IMPORTANT!
// 1. Needs to be anotated with @Dao
// 2. Appropriate annotation.
// 3. @Insert, @Delete, @Update
// methods cannot have any other argument
// other than type of the table entity.
// 4. @Query - needs to have an
// SQL query statement.
@Dao
interface Table1Dao {
@Insert(onConflict = OnConflictStrategy.ABORT) // onConflit optional. Default - ABORT
suspend fun insertRecord(record: Table1Entity)
@Delete
suspend fun deleteRecord(record: Table1Entity)
@Update
suspend fun updateRecord(record: Table1Entity)
@Query("SELECT * FROM Table1")
suspend fun getAllRecords(): List
// Note the table name in SQL query matches
// with @Entity annotation "tableName",
// present in the "Table1Entity" data class.
@Query("SELECT EXISTS(SELECT * FROM Table1 WHERE name is :name)")
suspend fun isPresent(name: String): Boolean
// This method checks if the name entry exists.
// Check how the method is passed to the query
// (using a colon :)
// We cannot use in argument like ${record.name}
// as dot operator is not supported.
// @Query can take only primary type variables.
}
// ===================================================================================
// Database class
// ===================================================================================
// This "connects" the entity data class
// and the DAO interface.
// IMPORTANT!
// 1. To be annotated with @Database,
// which takes input of array of entities,
// (thus it knows the table schemas).
// "version" is also mandatory.
// 2. Must be abstract class,
// extending "RoomDatabase" class.
// 3. Must have abstract functions with
// return type as DAO interface.
@Database(entities = [Table1Entity::class], version = 1)
abstract class AppDb: RoomDatabase() {
abstract fun table1Dao(): Table1Dao
}
// ===================================================================================
// Create instance of Database class
// For singleton, create in a kotlin file, not inside class.
// ===================================================================================
// Needs context for Room.databaseBuilder
// Argument 1 - context
// Argument 2 - previuosly defined
// database class extending RoomDatabase()
// Argument 3 - name of database file
// Creating database instance
// is an expensive operation.
// Hence we create once and
// store that in a variable.
private var DbSingleton : AppDb? = null
fun getAppDb(context: Context): AppDb {
return DbSingleton ?:
Room.databaseBuilder(context, AppDb::class.java, "Name.db").build().apply {
DbSingleton = this
}
}
// ===================================================================================
// Call the DAO interface functions
// Call inside a coroutine scope.
// ===================================================================================
// Call the previously defined getAppDb()
// function.
// This is an instance of "AppDb" class
// which contained "table1Dao()" function.
// Use that method to get the instance of
// DAO interface and then use the methods
// defined in "Table1Dao" interface.
class MainActivity: AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
CoroutineScope(IO).launch {
getAppDb(this@MainActivity).table1Dao().run {
insertRecord(
Table1Entity(0, "sample_name_776")
)
println("DB result: ${getAllRecords()}, size: ${getAllRecords().size}")
}
}
}
}
// ===================================================================================