示例/演示

Question

我正在编程小型应用程序，我为此留出了空间。 SQLite包装器。据我所知，代码中有些功能无法使用。此外，文档似乎非常不完整，或者有时甚至是错误的。例如，dao批注@Update和@Delete。我对使用此框架感到困惑，我想回到使用SQLite API来代替。您如何看待房间？

现在我要问的主要问题。我将向您展示我的代码，也许您会看到为什么无法正常工作。

首先，我的实体和刀。它应该代表一个音频文件。

from sqlalchemy import MetaData
from sqlalchemy.schema import CreateColumn
from sqlalchemy.ext.compiler import compiles


@compiles(CreateColumn, 'firebird')
def use_identity(element, compiler, **kw):
    text = compiler.visit_create_column(element, **kw)
    text = text.replace("SERIAL", "INT GENERATED BY DEFAULT AS IDENTITY")
    return text

m = MetaData()
t = Table(
    't', m,
    Column('id', Integer, primary_key=True),
    Column('data', String)
)

那是常规的数据库管理器。

@Entity(tableName = "audiofile")
public class AudioFile
{
    @PrimaryKey(autoGenerate = true)
    private long id;

    @ColumnInfo(name = "title")
    private String title;

    @ColumnInfo(name = "artist")
    private String artist;

    @ColumnInfo(name = "path")
    private String path;

    @ColumnInfo(name = "duration")
    private long duration;

@Dao
public interface AudioFileDao
{
    @Query("SELECT * FROM audiofile WHERE title LIKE :title")
    AudioFile getAudioFile(String title);

    @Query("SELECT * FROM audiofile")
    List<AudioFile> getAll();

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void initAudioFiles(AudioFile... audioFiles);

    @Update
    void updateAudioFile(AudioFile... audioFiles);

//        @Query("DELETE FROM audiofile WHERE id = :audioFileId")
    @Delete
    void deleteAudioFile(AudioFile audioFile);

    @Insert
    void insertAll(AudioFile... audioFiles);

    @Insert
    long insertAudioFile(AudioFile audioFile);
}

Aaa这是我的测试，引起了我的所有担忧：

@Database(entities = {AudioFile.class}, version = 1)
public abstract class DbManager extends RoomDatabase
{

    private static DbManager INSTANCE;

    public abstract AudioFile.AudioFileDao audioFileDao();

    public static DbManager getDbManager(Context ctx){
        if (INSTANCE == null){
            INSTANCE = Room.databaseBuilder(ctx.getApplicationContext(), DbManager.class, "playlist").build();
        }
        return INSTANCE;
    }

    public static void destroyInstance(){
        INSTANCE = null;
    }
}

预先感谢您的帮助。这东西使我发疯。

Answer 1

现在我要问的主要问题。我将向您展示我的代码，也许您会看到为什么无法正常工作。

我相信您的问题是，当您插入AudioFile时，未设置ID，因此在AudioFile对象audioFile中将其设置为0。但是，插入时，id将自动生成，并且不会为0，而是可能是某个时间插入的AudioFile对象的数量+1。

如果未设置 id 来使用同一AudioFile对象进行更新/删除，则会尝试使用ID 0 来更新删除。 不会有这样的行。

一个修复程序，假设AudioFile存在 setId 方法，但是可以使用：-

audioFile.setId(audioFileDao.insertAudioFile(audioFile));

可以处理不会导致异常的插入失败的修补程序可能是：-

long insertedId = audioFileDao.insertAudioFile(audioFile);
if (insertedId > 0) {
    audioFile.setId(insertedId);
} else {
    //......... handle not inserted
}

示例/演示

下面的代码在运行时显示上面的内容（您的Entity和Dao已被原样复制）：-

    ...... database built
    mAudioFileDao = mAppDB.audioFileDao();

    AudioFile a = new AudioFile();
    a.setTitle("MySong");
    a.setDuration(5);
    a.setArtist("Fred");
    a.setPath("/thepath");

    logAudioFile(a,"Before Insert into DB");
    long currentId = mAudioFileDao.insertAudioFile(a); //<<<<<<<<<< INSERT INTO DB
    logAudioFile(a,"Immediately after Insert. ID returned from insert is " + currentId);
    a.setId(currentId); //<<<<<<<<<< SET the the id of the AudioFile object a
    logAudioFile(a,"After setting the ID to " + currentId);
    mAudioFileDao.updateAudioFile(a);
    List<AudioFile> audioFileList = mAudioFileDao.getAll();
    for (AudioFile af: audioFileList) {
        logAudioFile(af,"Extracted from DB");
    }
    mAudioFileDao.deleteAudioFile(a);
    Log.d("AUDIOFILEINFO","Attempt to delete Audio File undertaken");
    audioFileList = mAudioFileDao.getAll();
    for (AudioFile af: audioFileList) {
        logAudioFile(af,"After deletion");
    }

logAudioFile 方法为：-

private void logAudioFile(AudioFile a, String extra) {
    Log.d(
            "AUDIOFILEINFO",
            "Title is " + a.getTitle() +
                    " ID is " + a.getId() +
                    "\n\tExtra Info is " + extra
    );
}

结果（从上面记录）：-

2019-10-06 11:03:39.757 D/AUDIOFILEINFO: Title is MySong ID is 0
        Extra Info is Before Insert into DB
2019-10-06 11:03:39.808 D/AUDIOFILEINFO: Title is MySong ID is 0
        Extra Info is Immediately after Insert. ID returned from insert is 1
2019-10-06 11:03:39.808 D/AUDIOFILEINFO: Title is MySong ID is 1
        Extra Info is After setting the ID to 1
2019-10-06 11:03:39.829 D/AUDIOFILEINFO: Title is MySong ID is 1
        Extra Info is Extracted from DB
2019-10-06 11:03:39.831 D/AUDIOFILEINFO: Attempt to delete Audio File undertaken

您如何看待房间？

那是在征求意见，话题也在外。

ROOM持久性库的更新和删除不会更改任何内容

1 个答案:

示例/演示

结果（从上面记录）：-