04-data-management

Master data persistence strategies for Android. Learn Room ORM (recommended), SQLite direct access, SharedPreferences, DataStore, and secure encryption. Understand schema design, migrations, and reactive data flows. Prerequisite: Fundamentals & Platform agents Duration: 62 hours | Level: Intermediate Topics: 8 major areas | Code Examples: 40+ real-world patterns ---

Room is the modern persistence layer providing type-safe database access with compile-time query verification.

`kotlin // Basic entity @Entity(tableName = "users") data class User( @PrimaryKey val id: Int, val name: String, val email: String, val createdAt: Long = System.currentTimeMillis(), // Ignore fields not stored in database @Ignore val isSelected: Boolean = false ) // Entity with customized column names @Entity(tableName = "products") data class Product( @PrimaryKey(autoGenerate = true) val id: Int = 0, @ColumnInfo(name = "product_name") val name: String, @ColumnInfo(name = "product_price") val price: Double, @ColumnInfo(typeAffinity = ColumnInfo.REAL) val rating: Float ) // Composite primary key @Entity(tableName = "order_items", primaryKeys = ["orderId", "productId"]) data class OrderItem( val orderId: Int, val productId: Int, val quantity: Int ) // Entity with foreign key (relationship) @Entity( tableName = "posts", foreignKeys = [ ForeignKey( entity = User::class, parentColumns = ["id"], childColumns = ["userId"], onDelete = ForeignKey.CASCADE // Delete posts when user deleted ) ], indices = [Index("userId")] // Index for faster queries ) data class Post( @PrimaryKey val id: Int, val userId: Int, val title: String, val content: String ) `

`kotlin @Dao interface UserDao { // Query single item @Query("SELECT * FROM users WHERE id = :userId") suspend fun getUser(userId: Int): User? // Query multiple items @Query("SELECT * FROM users ORDER BY name ASC") suspend fun getAllUsers(): List<User> // Reactive query with Flow (auto-updates on changes) @Query("SELECT * FROM users ORDER BY name ASC") fun observeAllUsers(): Flow<List<User>> // Filtered query with parameters @Query("SELECT * FROM users WHERE name LIKE :pattern") suspend fun searchByName(pattern: String): List<User> // Count rows @Query("SELECT COUNT(*) FROM users") suspend fun getUserCount(): Int // Insert single item @Insert(onConflict = OnConflictStrategy.REPLACE) suspend fun insertUser(user: User) // Insert multiple items @Insert(onConflict = OnConflictStrategy.IGNORE) suspend fun insertUsers(users: List<User>) // Update item @Update suspend fun updateUser(user: User) // Delete item @Delete suspend fun deleteUser(user: User) // Delete by condition @Query("DELETE FROM users WHERE id = :userId") suspend fun deleteUserById(userId: Int) // Upsert (Update or Insert) @Upsert suspend fun upsertUser(user: User) // Complex query with JOIN @Query(""" SELECT users.id, users.name, COUNT(posts.id) as postCount FROM users LEFT JOIN posts ON users.id = posts.userId GROUP BY users.id ORDER BY postCount DESC """) suspend fun getUsersWithPostCount(): List<UserWithPostCount> // Transaction (all or nothing) @Transaction @Query("SELECT * FROM users WHERE id = :userId") suspend fun getUserWithPosts(userId: Int): UserWithPosts } // Data class for JOIN results data class UserWithPostCount( val id: Int, val name: String, val postCount: Int ) // Relation for nested objects data class UserWithPosts( @Embedded val user: User, @Relation( parentColumn = "id", entityColumn = "userId" ) val posts: List<Post> ) `