在Android中使用Room进行数据迁移并添加外键引用的解决方法如下所示:
@Entity(tableName = "users")
data class User(
@PrimaryKey val id: Int,
val name: String
)
@Entity(tableName = "orders",
foreignKeys = [ForeignKey(
entity = User::class,
parentColumns = ["id"],
childColumns = ["userId"],
onDelete = ForeignKey.CASCADE
)])
data class Order(
@PrimaryKey val id: Int,
val userId: Int,
val amount: Double
)
up
方法中添加外键引用。class Migration1to2 : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL("CREATE TABLE orders_new (id INTEGER PRIMARY KEY NOT NULL, userId INTEGER NOT NULL, amount REAL NOT NULL, FOREIGN KEY(userId) REFERENCES users(id) ON DELETE CASCADE)")
database.execSQL("INSERT INTO orders_new (id, userId, amount) SELECT id, userId, amount FROM orders")
database.execSQL("DROP TABLE orders")
database.execSQL("ALTER TABLE orders_new RENAME TO orders")
}
}
@Database(entities = [User::class, Order::class], version = 2)
abstract class AppDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
abstract fun orderDao(): OrderDao
companion object {
private const val DATABASE_NAME = "myapp.db"
fun buildDatabase(context: Context): AppDatabase {
return Room.databaseBuilder(context, AppDatabase::class.java, DATABASE_NAME)
.addMigrations(Migration1to2())
.build()
}
}
}
Room.databaseBuilder(context, AppDatabase::class.java, DATABASE_NAME)
.addMigrations(Migration1to2(), Migration2to3())
.build()
这样,你就可以在使用Room进行数据迁移时添加外键引用了。