android - 尝试从 Room 数据库实例中检索值时抛出 IllegalStateException

Question

我正在使用 android 新架构组件 room 进行数据库操作，当我尝试从数据库中检索对象时遇到了麻烦

Couldn't read row 0, col 0 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.

这是我的 Dao 界面

@Dao
interface BookDao {
    @Query("SELECT * FROM books")
    fun getAllBooks() : List<Book>

    @Insert
    fun saveBook(book: Book)

    @Query("DELETE FROM books")
    fun deleteBookTable()
}

那是我的表模型类

@Entity(tableName = "books")
data class Book(
        @ColumnInfo(name = "book_title")
        var title: String,
        var imgRes: Int,
        var filePath: String? = null,
        var pdfInBytes: ByteArray? = null,
        @PrimaryKey
        @ColumnInfo(name = "_id")
        var bookId: String = UUID.randomUUID().toString()
) : Serializable

这是 RoomDatabase 子类

@Database(entities = arrayOf(Book::class), version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun bookDao(): BookDao

    companion object {

         @Volatile private var INSTANCE: AppDatabase? = null

         fun getInstance(context: Context): AppDatabase =
             INSTANCE ?: synchronized(this) {
             INSTANCE ?: buildDatabase(context).also { INSTANCE = it }
         }

         private fun buildDatabase(context: Context) =
             Room.databaseBuilder(context.applicationContext,
                    AppDatabase::class.java, "booksDB.db")
                    .build()
    }
}

这是我调用这个方法的代码

private val db: AppDatabase by lazy { AppDatabase.getInstance(this) }

override fun onCreate(savedInstanceState: Bundle?) {
    doAsync { // from anko library
       for (i in 0..10){
           val book = Book("$i", tmpImgRes, "tmpPath", tmpBytes)
           db.bookDao().saveBook(book)
       }
       val books = db.bookDao().getAllBooks()
   }
}

当我尝试调用 getAllBooks() 时抛出异常。

房间实现:

implementation "android.arch.persistence.room:runtime:1.0.0-rc1"
annotationProcessor "android.arch.persistence.room:compiler:1.0.0-rc1"

Answer 1

我解决了我的问题，实际问题，在 SQLite 表行大小中，当我试图从表中获取数据时，该行包含超过 2.5 MB 的数据并且在 SQLite 数据库中不是很好，比我通过拆分字节数组并按 block 保存它来减少数据的大小，之后每件事都完美地工作，在获取之后我将它合并为原​​始数据