我正在編寫小型應(yīng)用程序，并為其使用空間。SQLite 包裝器。就我的代碼工作而言，有一些功能不起作用。此外，文檔似乎非常不完整，或者在某些方面是錯(cuò)誤的。例如dao注解@Update和@Delete。我慢慢地對(duì)使用這個(gè)框架感到困惑，并且我考慮重新使用 SQLite API 而不是它。您對(duì)房間有何看法？現(xiàn)在是我想問(wèn)的主要問(wèn)題。我將向您展示我的代碼，也許您會(huì)明白為什么不能正常工作。首先，我的實(shí)體和道。它應(yīng)該代表一個(gè)音頻文件。@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;@Daopublic 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);}那是常規(guī)的數(shù)據(jù)庫(kù)管理器。@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; }}
1 回答
慕標(biāo)琳琳
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現(xiàn)在是我想問(wèn)的主要問(wèn)題。我將向您展示我的代碼，也許您會(huì)明白為什么不能正常工作。
我相信您的問(wèn)題是，當(dāng)您插入 AudioFile 時(shí)，未設(shè)置 id，因此 AudioFile 對(duì)象 audioFile 中的 id 為 0。但是，插入時(shí)，id 將自動(dòng)生成，并且不會(huì)為 0，而可能是某個(gè)時(shí)間插入的 AudioFile 對(duì)象的數(shù)量 + 1。
如果不設(shè)置id，則使用相同的 AudioFile 對(duì)象來(lái)更新/刪除將嘗試使用0的 id 來(lái)更新刪除。不會(huì)有這樣的行。
假設(shè)AudioFile 存在setId方法，但不處理失敗的插入，可以使用以下修復(fù)：-
audioFile.setId(audioFileDao.insertAudioFile(audioFile));
可以處理未導(dǎo)致異常的失敗插入的修復(fù)可能是：-
long insertedId = audioFileDao.insertAudioFile(audioFile);
if (insertedId > 0) {
audioFile.setId(insertedId);
} else {
//......... handle not inserted
}
示例/演示
以下代碼運(yùn)行時(shí)顯示上述內(nèi)容（您的 Entity 和 Dao 已按原樣復(fù)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方法是： -
private void logAudioFile(AudioFile a, String extra) {
Log.d(
"AUDIOFILEINFO",
"Title is " + a.getTitle() +
" ID is " + a.getId() +
"\n\tExtra Info is " + extra
);
}
結(jié)果（上面的日志）：-
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
您對(duì)房間有何看法？
這是征求意見，所以是題外話。
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