我正在使用 Room 数据库,我更新了我的模型。这就是我进行迁移的原因,以免删除现有数据。我尝试在迁移时在 SQL 代码中添加位图,但出现错误。如何使用 SQL 代码添加位图?
型号:
@Entity(tableName = "person_table")
data class PersonModel(
@PrimaryKey(autoGenerate = true)
val id: Int,
val name: String,
val surname: String,
val profilePicture: Bitmap
)
数据库:
@Database(entities = [PersonModel::class], version = 2, exportSchema = true)
@TypeConverters(Converter::class)
abstract class PersonDatabase : RoomDatabase() {
abstract fun personDao(): PersonDao
companion object {
@Volatile
private var INSTANCE: PersonDatabase? = null
fun getDatabase(context: Context): PersonDatabase {
return INSTANCE ?: synchronized(this) {
val instance = Room.databaseBuilder(
context.applicationContext,
PersonDatabase::class.java,
"PersonDatabase"
).addMigrations(MIGRATION_1_2)
.build()
INSTANCE = instance
instance
}
}
val MIGRATION_1_2 = object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL(
"ALTER TABLE person_table ADD COLUMN profilePicture BITMAP"
)
}
}
}
}
转换器:
class Converter {
@TypeConverter
fun fromBitmap(bitmap: Bitmap): ByteArray {
val outputStream = ByteArrayOutputStream()
bitmap.compress(Bitmap.CompressFormat.PNG, 100, outputStream)
return outputStream.toByteArray()
}
@TypeConverter
fun toBitmap(byteArray: ByteArray): Bitmap {
return BitmapFactory.decodeByteArray(byteArray, 0, byteArray.size)
}
}
Room 不支持位图,但支持 BLOB 类型,所以你可以这样使用
@ColumnInfo(typeAffinity = ColumnInfo.BLOB)
val profilePicture: ByteArray? = null
并添加扩展以将位图转换为字节数组
fun Bitmap.toByteArray(quality: Int = 50): ByteArray {
val stream = ByteArrayOutputStream()
compress(Bitmap.CompressFormat.JPEG, quality, stream)
return stream.toByteArray()
}
正如@Александр提到的,Room不支持位图,但支持BLOB类型。 据此,您提供的解决方案有两个错误:
val MIGRATION_1_2 = object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL(
"ALTER TABLE person_table ADD COLUMN profilePicture BLOB"
)
}
}
所以,应该是
BLOB
而不是BITMAP
,那么:
@Entity(tableName = "person_table")
data class PersonModel(
@PrimaryKey(autoGenerate = true)
val id: Int,
val name: String,
val surname: String,
@ColumnInfo(typeAffinity = ColumnInfo.BLOB)
val profilePicture: Bitmap
)
它仍然可以是
Bitmap
,但您应该添加 typeAffinity
并保留您的转换器。
而且,@Александр 的解决方案也有效:)