Room增加数据表迁移小结

• Room使用注解方式增加数据表，进行迁移示例

  • 1 使用@Entity注解增加实体类，示例：

    
    @Entity(tableName = "notice")
    
    data class NoticeBean(
    
      @PrimaryKey(autoGenerate = true)var id: Int = 0，
    
      @ColumnInfo(name = "orderId")var orderId: Int = 0,
    
      @ColumnInfo(name = "title")var title: String? =""
    
    )
    
    

  • 2 在数据库持有者AppDatabase中增加创建的实体类，并更改version = 3(我原来version = 2)，示例：

    
      @Database(entities = arrayOf(GrabOrderBean::class,NoticeBean::class),version = 3)
    
      abstract class AppDatabase : RoomDatabase() {}
    
    

  • 3 增加Migration并addMigrations，示例：

    
        val MIGRATION_2_3 =object : Migration(2,3) {
    
        override fun migrate(database: SupportSQLiteDatabase) {
    
        database.execSQL("CREATE TABLE IF NOT EXISTS notice (orderId INTEGER NOT NULL, title TEXT, " +
    
        "id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL)")
    
        }
    
      }
    
        private fun buildDatabase(context: Context) = Room.databaseBuilder(context.applicationContext,
    
        AppDatabase::class.java,"test.db")
    
        .allowMainThreadQueries()
    
        .addMigrations(MIGRATION_1_2,MIGRATION_2_3)
    
        .build()
    
    

  • 4 注意事项

      在定义实体类时orderId 有默认值，所以在执行execSQL时需使用orderId INTEGER NOT NULL，否则在运行时有可能会报异常。