Room 2.x का इस्तेमाल करके, डेटा को किसी स्थानीय डेटाबेस में सेव करना

dependencies {
    val room_version = "2.6.1"

    implementation("androidx.room:room-runtime:$room_version")
    annotationProcessor("androidx.room:room-compiler:$room_version")

    // To use Kotlin Symbol Processing (KSP)
    // ksp("androidx.room:room-compiler:$room_version")

    // optional - Kotlin Extensions and Coroutines support for Room
    implementation("androidx.room:room-ktx:$room_version")

    // optional - RxJava2 support for Room
    implementation("androidx.room:room-rxjava2:$room_version")

    // optional - Guava support for Room, including Optional and ListenableFuture
    implementation("androidx.room:room-guava:$room_version")

    // optional - Test helpers
    testImplementation("androidx.room:room-testing:$room_version")
}

// Entity
@Entity
data class User(
    @PrimaryKey val uid: Int,
    @ColumnInfo(name = "first_name") val firstName: String?,
    @ColumnInfo(name = "last_name") val lastName: String?
)

// DAO
@Dao
interface UserDao {
    @Query("SELECT * FROM user")
    fun getAll(): List<User>

    @Insert
    fun insertAll(vararg users: User)

    @Delete
    fun delete(user: User)
}

// Database
@Database(entities = [User::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun userDao(): UserDao
}

// Usage
val db = Room.databaseBuilder(
            applicationContext,
            AppDatabase::class.java, "database-name"
        ).build()

val userDao = db.userDao()
val users: List<User> = userDao.getAll()

@Entity(tableName = "users")
data class User (
    @PrimaryKey val id: Int,
    @ColumnInfo(name = "first_name") val firstName: String?,
    @ColumnInfo(name = "last_name") val lastName: String?,
    @Ignore val picture: Bitmap? = null
)

class Converters {
  @TypeConverter
  fun fromTimestamp(value: Long?): Date? = value?.let { Date(it) }

  @TypeConverter
  fun dateToTimestamp(date: Date?): Long? = date?.time
}

// Register in your Database class
@Database(entities = [User::class], version = 1)
@TypeConverters(Converters::class)
abstract class AppDatabase : RoomDatabase() { ... }

@Dao
interface UserDao {
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertUsers(vararg users: User)

    @Update
    fun updateUsers(vararg users: User)

    @Delete
    fun deleteUsers(vararg users: User)
}

@Dao
interface UserDao {
    // Simple query
    @Query("SELECT * FROM user")
    fun loadAllUsers(): Array<User>

    // Return a subset of columns using a POJO or tuple
    @Query("SELECT first_name, last_name FROM user")
    fun loadFullName(): List<NameTuple>

    // Pass parameters
    @Query("SELECT * FROM user WHERE age > :minAge")
    fun loadAllUsersOlderThan(minAge: Int): Array<User>

    // Collection of parameters
    @Query("SELECT * FROM user WHERE region IN (:regions)")
    fun loadUsersFromRegions(regions: List<String>): List<User>

    // Join tables
    @Query("SELECT * FROM book INNER JOIN user ON user.id = book.user_id WHERE user.name = :userName")
    fun findBooksBorrowedByName(userName: String): List<Book>
}

@Query("SELECT * FROM user JOIN book ON user.id = book.user_id")
fun loadUserAndBookNames(): Map<User, List<Book>>

@Dao
interface UserDao {
    // One-shot async query
    @Insert
    suspend fun insertUsers(vararg users: User)

    // Observable query using Flow
    @Query("SELECT * FROM user WHERE id = :id")
    fun loadUserById(id: Int): Flow<User>
}

@Dao
interface UserDao {
    @Insert
    fun insertUsers(users: List<User>): Completable

    @Query("SELECT * FROM user WHERE id = :id")
    fun loadUserById(id: Int): Flowable<User>
}

@Dao
interface UserDao {
    // LiveData for observable queries
    @Query("SELECT * FROM user WHERE id = :id")
    fun loadUserById(id: Int): LiveData<User>

    // Guava ListenableFuture for one-shot queries
    @Insert
    fun insertUsers(users: List<User>): ListenableFuture<Integer>
}

@Entity
data class User(@PrimaryKey val userId: Long, val name: String)

@Entity
data class Library(@PrimaryKey val libraryId: Long, val userOwnerId: Long)

// Intermediate class
data class UserAndLibrary(
    @Embedded val user: User,
    @Relation(
         parentColumn = "userId",
         entityColumn = "userOwnerId"
    )
    val library: Library
)

// DAO Query
@Transaction
@Query("SELECT * FROM User")
fun getUsersAndLibraries(): List<UserAndLibrary>

@Entity
data class Playlist(@PrimaryKey val playlistId: Long, val userCreatorId: Long)

data class UserWithPlaylists(
    @Embedded val user: User,
    @Relation(
          parentColumn = "userId",
          entityColumn = "userCreatorId"
    )
    val playlists: List<Playlist>
)

@Entity
data class Song(@PrimaryKey val songId: Long, val songName: String)

@Entity(primaryKeys = ["playlistId", "songId"])
data class PlaylistSongCrossRef(val playlistId: Long, val songId: Long)

data class PlaylistWithSongs(
    @Embedded val playlist: Playlist,
    @Relation(
         parentColumn = "playlistId",
         entityColumn = "songId",
         associateBy = Junction(PlaylistSongCrossRef::class)
    )
    val songs: List<Song>
)

data class UserWithPlaylistsAndSongs(
      @Embedded val user: User,
      @Relation(
          entity = Playlist::class,
          parentColumn = "userId",
          entityColumn = "userCreatorId"
      )
      val playlists: List<PlaylistWithSongs> // Nesting PlaylistWithSongs
  )

@DatabaseView("SELECT user.id, user.name, department.name AS departmentName FROM user INNER JOIN department ON user.departmentId = department.id")
data class UserDetail(val id: Long, val name: String, val departmentName: String)

// Register in Database class
@Database(entities = [User::class], views = [UserDetail::class], version = 1)
abstract class AppDatabase : RoomDatabase() { ... }

Room.databaseBuilder(appContext, AppDatabase::class.java, "Sample.db")
    .createFromAsset("database/myapp.db")
    .build()

val MIGRATION_1_2 = object : Migration(1, 2) {
  override fun migrate(database: SupportSQLiteDatabase) {
    database.execSQL("ALTER TABLE User ADD COLUMN age INTEGER NOT NULL DEFAULT 0")
  }
}

Room.databaseBuilder(applicationContext, AppDatabase::class.java, "database-name")
  .addMigrations(MIGRATION_1_2)
  .build()

@RunWith(AndroidJUnit4::class)
class MigrationTest {
    @get:Rule
    val helper: MigrationTestHelper = MigrationTestHelper(
            InstrumentationRegistry.getInstrumentation(),
            AppDatabase::class.java.canonicalName,
            FrameworkSQLiteOpenHelperFactory()
    )

    @Test
    fun migrate1To2() {
        var db = helper.createDatabase("test-db", 1).apply {
            execSQL("INSERT INTO User VALUES (1, 'John')")
            close()
        }
        db = helper.runMigrationsAndValidate("test-db", 2, true, MIGRATION_1_2)
        // Verify data was migrated correctly
    }
}