Question

我正在使用Kotlin语言开发一个Android项目，并且正在使用android体系结构组件中的Room数据库。这些都是我的Room数据库资料。我试图让用户保存有关书籍的信息，当我在应用程序中时，它可以正常工作，但是当我重新启动应用程序时，所有内容都已删除。我需要将数据存储在内存中，因此我正在使用inMemoryDatabaseBuilder，但它似乎不起作用。任何帮助表示赞赏。

依赖项：

dependencies {
    def room_version = "1.1.1"
    implementation "android.arch.persistence.room:runtime:$room_version"
    kapt "android.arch.persistence.room:compiler:$room_version"
}

apply plugin: 'kotlin-kapt'

实体：

@Entity(tableName = "tblBooks")
data class BookData(@PrimaryKey(autoGenerate = true) var id: Long?,
                    @ColumnInfo(name = "name") var name: String,
                    @ColumnInfo(name = "author") var author: String,
                    @ColumnInfo(name = "translator") var translator: String,
                    @ColumnInfo(name = "publisher") var publisher: String,
                    @ColumnInfo(name = "publication_year") var publicationYear: Int?,
                    @ColumnInfo(name = "price") var price: Int?,
                    @ColumnInfo(name = "description") var description: String,
                    @ColumnInfo(name = "category") var category: String,
                    @ColumnInfo(name = "shelf_number") var shelfNumber: Int?,
                    @ColumnInfo(name = "front_cover") var frontCover: String?,
                    @ColumnInfo(name = "back_cover") var backCover: String?
){
    constructor():this(null, "", "", "", "", 0, 0, "", "",
            0, "", "")
}

道：

@Dao
interface BookDataDao {

    @Query("SELECT * FROM tblBooks")
    fun getAll(): List<BookData>

    @Insert(onConflict = REPLACE)
    fun insert(bookData: BookData)


}

数据库：

@Database(entities = [BookData::class], version = 1)
abstract class BookDatabase: RoomDatabase(){

    abstract fun bookDataDao(): BookDataDao

    companion object {
        private var INSTANCE: BookDatabase? = null

        fun getInstance(context: Context): BookDatabase? {
            if (INSTANCE == null){
                synchronized(BookDatabase::class){
                    INSTANCE = 
                    Room.inMemoryDatabaseBuilder(context.applicationContext,
                            BookDatabase::class.java).build()
                }
            }
            return INSTANCE
        }
    }
}

用法： 插入数据：

val database = BookDatabase.getInstance(this) !!
database.bookDataDao().insert(bookData)

检索数据：

val database = BookDatabase.getInstance(this) !!
val booksList = database.bookDataDao().getAll()

Answer 1

如果仅存储在内存中，通常在应用程序启动之间数据库不会持久存在。根据{{3}}：

杀死进程后，存储在内存数据库中的信息会消失

这意味着您每次杀死应用程序时，数据库也会关闭。如果您希望它具有持久性，则应改用标准的databaseBuilder，它将被放置在设备存储中。

会议室数据库丢失数据

1 个答案: