如何使用 Android Room Database 并使用 SQLite 的 Case Expression 进行查询

【问题标题】：how to use Android Room Database and query using SQLite's Case Expression如何使用 Android Room Database 并使用 SQLite 的 Case Expression 进行查询
【发布时间】：2021-12-04 16:20:37
【问题描述】：

我有一个房间数据库，其中包含具有各种 ColumnInfo 的媒体存储数据，例如标题、添加日期、作曲家、专辑、艺术家等

现在简单的媒体存储查询是，

cursor = context.getContentResolver().query(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, columns(),MediaStore.Audio.Media.IS_MUSIC + " = 1", null, SortOrder);

Where SortOrder = MediaStore.Audio.Media.TITLE等

我想用同样的逻辑来查询 ColumnInfo 所在的 Room 数据库

@PrimaryKey(autoGenerate = true)

public long _Id;
    
public long _SongId;

public String _title;

public String _album;

public long _albumId;

public String _artist;

public long _artistId;

public String _path;

public int _trackNumber;

public long _duration;

public String _year;

public String _composer;

public String _dateAdded;

我看过this

基本上我想使用该列的名称查询每个列并使用 ASC 或 DESC 进行排序

我们该怎么做。

【问题讨论】：

    标签： android sqlite android-room


    【解决方案1】：

    你可以使用类似的东西：-

    @Query("SELECT * FROM mediaentity ORDER BY " +
        "CASE WHEN lower(:sortByColumn) = lower('_id') AND :sortDirection THEN _id END ASC," +
        "CASE WHEN lower(:sortByColumn) = lower('_id') AND NOT :sortDirection THEN _id END DESC," +
        "CASE WHEN lower(:sortByColumn) = lower('_SongId') AND :sortDirection THEN _SongId END ASC, " +
        "CASE WHEN lower(:sortByColumn) = lower('_SongId') AND  NOT :sortDirection THEN _SongId END DESC," +
        "CASE WHEN lower(:sortByColumn) = lower('_title') AND :sortDirection THEN _title END ASC, " +
        "CASE WHEN lower(:sortByColumn) = lower('_title') AND NOT :sortDirection THEN _title END DESC " +
        // and so on, noting the comma except on the last
        ";"
)
abstract List<MediaEntity> getSortedMediaList(String sortByColumn, boolean sortDirection);
    • 使用内置 SQLite lower 函数可以省略表达式两边。

    或者更简单，但不太安全，您可以使用类似的东西：-

    @RawQuery
abstract List<MediaEntity> rawQuery(SupportSQLiteQuery qry);

public List<MediaEntity> getSortedMediaListV2(String sortByColumn, boolean sortDirection) {
    String sortOrder = " ASC ";
    if (!sortDirection) {
        sortOrder = " DESC";
    }
    String query = "SELECT * FROM mediaentity ORDER BY " + sortByColumn + sortOrder;
    return rawQuery(new SimpleSQLiteQuery(query));
}
    • 但是，如果您传递的列名不正确，则会失败。

    也许考虑以下利用上述内容的工作示例，最后显示如果使用了不正确的列名会发生什么：-

        db = TheDatabase.getInstance(this);
    dao = db.getAllDao();
    dao.deleteAll();
    dao.insert(new MediaEntity(100,"Breathe","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",5,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(99,"Speak to Me","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",4,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(98,"On the Run","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",3,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(102,"Time","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",10,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(97,"The Great Gig in the Sky","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",9,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(101,"Money","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",8,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(103,"Us and Them","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",7,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(96,"Any Colour You Like","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",1,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(104,"Brain Damage","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",6,180,"1971","Pink Floyd","2021-10-10"));
    dao.insert(new MediaEntity(95,"Eclipse","Dark Side of the Moon",100100,"Pink Floyd",100,"path to DSOTM",2,180,"1971","Pink Floyd","2021-10-10"));

    Log.d("MEDIAINFO","EXTRACT 1 -  ID ascending");
    for(MediaEntity m: dao.getSortedMediaList("_Id",true)) {
        Log.d("MEDIAINFO","ID = " + m._Id + " SongId = " + m._SongId + " Title = " + m._title + " track# = " + m._trackNumber + " Album is " + m._album);
    }
    Log.d("MEDIAINFO","EXTRACT 2 - ID descending");
    for(MediaEntity m: dao.getSortedMediaList("_Id",false)) {
        Log.d("MEDIAINFO","ID = " + m._Id + " SongId = " + m._SongId + " Title = " + m._title + " track# = " + m._trackNumber + " Album is " + m._album);
    }
    Log.d("MEDIAINFO","EXTRACT 3 - Title ascending");
    for(MediaEntity m: dao.getSortedMediaList("_title",true)) {
        Log.d("MEDIAINFO","ID = " + m._Id + " SongId = " + m._SongId + " Title = " + m._title + " track# = " + m._trackNumber + " Album is " + m._album);
    }
    Log.d("MEDIAINFO","EXTRACT 4 - Title descending");
    for(MediaEntity m: dao.getSortedMediaList("_title",false)) {
        Log.d("MEDIAINFO","ID = " + m._Id + " SongId = " + m._SongId + " Title = " + m._title + " track# = " + m._trackNumber + " Album is " + m._album);
    }
    Log.d("MEDIAINFO","EXTRACT 5 - SongId ascending");
    for(MediaEntity m: dao.getSortedMediaList("_SongId",true)) {
        Log.d("MEDIAINFO","ID = " + m._Id + " SongId = " + m._SongId + " Title = " + m._title + " track# = " + m._trackNumber + " Album is " + m._album);
    }
    Log.d("MEDIAINFO","EXTRACT 6 - SongId descending");
    for(MediaEntity m: dao.getSortedMediaList("_SongId",false)) {
        Log.d("MEDIAINFO","ID = " + m._Id + " SongId = " + m._SongId + " Title = " + m._title + " track# = " + m._trackNumber + " Album is " + m._album);
    }

    Log.d("MEDIAINFO","EXTRACT 7 - TrackNumber ascending");
    for(MediaEntity m: dao.getSortedMediaListV2("_tracknumber",true)) {
        Log.d("MEDIAINFO","ID = " + m._Id + " SongId = " + m._SongId + " Title = " + m._title + " track# = " + m._trackNumber + " Album is " + m._album);
    }
    Log.d("MEDIAINFO","EXTRACT 8 - TrackNumber descending");
    for(MediaEntity m: dao.getSortedMediaListV2("_tracknumber",false)) {
        Log.d("MEDIAINFO","ID = " + m._Id + " SongId = " + m._SongId + " Title = " + m._title + " track# = " + m._trackNumber + " Album is " + m._album);
    }

    dao.getSortedMediaList("not a known column", true);
    dao.getSortedMediaListV2("not a known column", true);

    日志的输出包括：-

    2021-10-18 11:42:48.938 D/MEDIAINFO: EXTRACT 1 -  ID ascending
2021-10-18 11:42:48.946 D/MEDIAINFO: ID = 1 SongId = 100 Title = Breathe track# = 5 Album is Dark Side of the Moon
2021-10-18 11:42:48.946 D/MEDIAINFO: ID = 2 SongId = 99 Title = Speak to Me track# = 4 Album is Dark Side of the Moon
2021-10-18 11:42:48.946 D/MEDIAINFO: ID = 3 SongId = 98 Title = On the Run track# = 3 Album is Dark Side of the Moon
2021-10-18 11:42:48.946 D/MEDIAINFO: ID = 4 SongId = 102 Title = Time track# = 10 Album is Dark Side of the Moon
2021-10-18 11:42:48.946 D/MEDIAINFO: ID = 5 SongId = 97 Title = The Great Gig in the Sky track# = 9 Album is Dark Side of the Moon
2021-10-18 11:42:48.947 D/MEDIAINFO: ID = 6 SongId = 101 Title = Money track# = 8 Album is Dark Side of the Moon
2021-10-18 11:42:48.947 D/MEDIAINFO: ID = 7 SongId = 103 Title = Us and Them track# = 7 Album is Dark Side of the Moon
2021-10-18 11:42:48.947 D/MEDIAINFO: ID = 8 SongId = 96 Title = Any Colour You Like track# = 1 Album is Dark Side of the Moon
2021-10-18 11:42:48.947 D/MEDIAINFO: ID = 9 SongId = 104 Title = Brain Damage track# = 6 Album is Dark Side of the Moon
2021-10-18 11:42:48.947 D/MEDIAINFO: ID = 10 SongId = 95 Title = Eclipse track# = 2 Album is Dark Side of the Moon
2021-10-18 11:42:48.947 D/MEDIAINFO: EXTRACT 2 - ID descending
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 10 SongId = 95 Title = Eclipse track# = 2 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 9 SongId = 104 Title = Brain Damage track# = 6 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 8 SongId = 96 Title = Any Colour You Like track# = 1 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 7 SongId = 103 Title = Us and Them track# = 7 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 6 SongId = 101 Title = Money track# = 8 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 5 SongId = 97 Title = The Great Gig in the Sky track# = 9 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 4 SongId = 102 Title = Time track# = 10 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 3 SongId = 98 Title = On the Run track# = 3 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 2 SongId = 99 Title = Speak to Me track# = 4 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: ID = 1 SongId = 100 Title = Breathe track# = 5 Album is Dark Side of the Moon
2021-10-18 11:42:48.949 D/MEDIAINFO: EXTRACT 3 - Title ascending
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 8 SongId = 96 Title = Any Colour You Like track# = 1 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 9 SongId = 104 Title = Brain Damage track# = 6 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 1 SongId = 100 Title = Breathe track# = 5 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 10 SongId = 95 Title = Eclipse track# = 2 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 6 SongId = 101 Title = Money track# = 8 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 3 SongId = 98 Title = On the Run track# = 3 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 2 SongId = 99 Title = Speak to Me track# = 4 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 5 SongId = 97 Title = The Great Gig in the Sky track# = 9 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 4 SongId = 102 Title = Time track# = 10 Album is Dark Side of the Moon
2021-10-18 11:42:48.955 D/MEDIAINFO: ID = 7 SongId = 103 Title = Us and Them track# = 7 Album is Dark Side of the Moon
2021-10-18 11:42:48.956 D/MEDIAINFO: EXTRACT 4 - Title descending
2021-10-18 11:42:48.959 D/MEDIAINFO: ID = 7 SongId = 103 Title = Us and Them track# = 7 Album is Dark Side of the Moon
2021-10-18 11:42:48.959 D/MEDIAINFO: ID = 4 SongId = 102 Title = Time track# = 10 Album is Dark Side of the Moon
2021-10-18 11:42:48.959 D/MEDIAINFO: ID = 5 SongId = 97 Title = The Great Gig in the Sky track# = 9 Album is Dark Side of the Moon
2021-10-18 11:42:48.959 D/MEDIAINFO: ID = 2 SongId = 99 Title = Speak to Me track# = 4 Album is Dark Side of the Moon
2021-10-18 11:42:48.959 D/MEDIAINFO: ID = 3 SongId = 98 Title = On the Run track# = 3 Album is Dark Side of the Moon
2021-10-18 11:42:48.960 D/MEDIAINFO: ID = 6 SongId = 101 Title = Money track# = 8 Album is Dark Side of the Moon
2021-10-18 11:42:48.960 D/MEDIAINFO: ID = 10 SongId = 95 Title = Eclipse track# = 2 Album is Dark Side of the Moon
2021-10-18 11:42:48.960 D/MEDIAINFO: ID = 1 SongId = 100 Title = Breathe track# = 5 Album is Dark Side of the Moon
2021-10-18 11:42:48.960 D/MEDIAINFO: ID = 9 SongId = 104 Title = Brain Damage track# = 6 Album is Dark Side of the Moon
2021-10-18 11:42:48.960 D/MEDIAINFO: ID = 8 SongId = 96 Title = Any Colour You Like track# = 1 Album is Dark Side of the Moon
2021-10-18 11:42:48.960 D/MEDIAINFO: EXTRACT 5 - SongId ascending
2021-10-18 11:42:48.965 D/MEDIAINFO: ID = 10 SongId = 95 Title = Eclipse track# = 2 Album is Dark Side of the Moon
2021-10-18 11:42:48.965 D/MEDIAINFO: ID = 8 SongId = 96 Title = Any Colour You Like track# = 1 Album is Dark Side of the Moon
2021-10-18 11:42:48.965 D/MEDIAINFO: ID = 5 SongId = 97 Title = The Great Gig in the Sky track# = 9 Album is Dark Side of the Moon
2021-10-18 11:42:48.966 D/MEDIAINFO: ID = 3 SongId = 98 Title = On the Run track# = 3 Album is Dark Side of the Moon
2021-10-18 11:42:48.966 D/MEDIAINFO: ID = 2 SongId = 99 Title = Speak to Me track# = 4 Album is Dark Side of the Moon
2021-10-18 11:42:48.966 D/MEDIAINFO: ID = 1 SongId = 100 Title = Breathe track# = 5 Album is Dark Side of the Moon
2021-10-18 11:42:48.966 D/MEDIAINFO: ID = 6 SongId = 101 Title = Money track# = 8 Album is Dark Side of the Moon
2021-10-18 11:42:48.966 D/MEDIAINFO: ID = 4 SongId = 102 Title = Time track# = 10 Album is Dark Side of the Moon
2021-10-18 11:42:48.967 D/MEDIAINFO: ID = 7 SongId = 103 Title = Us and Them track# = 7 Album is Dark Side of the Moon
2021-10-18 11:42:48.967 D/MEDIAINFO: ID = 9 SongId = 104 Title = Brain Damage track# = 6 Album is Dark Side of the Moon
2021-10-18 11:42:48.967 D/MEDIAINFO: EXTRACT 6 - SongId descending
2021-10-18 11:42:48.971 D/MEDIAINFO: ID = 9 SongId = 104 Title = Brain Damage track# = 6 Album is Dark Side of the Moon
2021-10-18 11:42:48.972 D/MEDIAINFO: ID = 7 SongId = 103 Title = Us and Them track# = 7 Album is Dark Side of the Moon
2021-10-18 11:42:48.972 D/MEDIAINFO: ID = 4 SongId = 102 Title = Time track# = 10 Album is Dark Side of the Moon
2021-10-18 11:42:48.972 D/MEDIAINFO: ID = 6 SongId = 101 Title = Money track# = 8 Album is Dark Side of the Moon
2021-10-18 11:42:48.972 D/MEDIAINFO: ID = 1 SongId = 100 Title = Breathe track# = 5 Album is Dark Side of the Moon
2021-10-18 11:42:48.972 D/MEDIAINFO: ID = 2 SongId = 99 Title = Speak to Me track# = 4 Album is Dark Side of the Moon
2021-10-18 11:42:48.972 D/MEDIAINFO: ID = 3 SongId = 98 Title = On the Run track# = 3 Album is Dark Side of the Moon
2021-10-18 11:42:48.972 D/MEDIAINFO: ID = 5 SongId = 97 Title = The Great Gig in the Sky track# = 9 Album is Dark Side of the Moon
2021-10-18 11:42:48.972 D/MEDIAINFO: ID = 8 SongId = 96 Title = Any Colour You Like track# = 1 Album is Dark Side of the Moon
2021-10-18 11:42:48.973 D/MEDIAINFO: ID = 10 SongId = 95 Title = Eclipse track# = 2 Album is Dark Side of the Moon
2021-10-18 11:42:48.973 D/MEDIAINFO: EXTRACT 7 - TrackNumber ascending
2021-10-18 11:42:48.977 D/MEDIAINFO: ID = 8 SongId = 96 Title = Any Colour You Like track# = 1 Album is Dark Side of the Moon
2021-10-18 11:42:48.978 D/MEDIAINFO: ID = 10 SongId = 95 Title = Eclipse track# = 2 Album is Dark Side of the Moon
2021-10-18 11:42:48.978 D/MEDIAINFO: ID = 3 SongId = 98 Title = On the Run track# = 3 Album is Dark Side of the Moon
2021-10-18 11:42:48.978 D/MEDIAINFO: ID = 2 SongId = 99 Title = Speak to Me track# = 4 Album is Dark Side of the Moon
2021-10-18 11:42:48.978 D/MEDIAINFO: ID = 1 SongId = 100 Title = Breathe track# = 5 Album is Dark Side of the Moon
2021-10-18 11:42:48.979 D/MEDIAINFO: ID = 9 SongId = 104 Title = Brain Damage track# = 6 Album is Dark Side of the Moon
2021-10-18 11:42:48.979 D/MEDIAINFO: ID = 7 SongId = 103 Title = Us and Them track# = 7 Album is Dark Side of the Moon
2021-10-18 11:42:48.979 D/MEDIAINFO: ID = 6 SongId = 101 Title = Money track# = 8 Album is Dark Side of the Moon
2021-10-18 11:42:48.979 D/MEDIAINFO: ID = 5 SongId = 97 Title = The Great Gig in the Sky track# = 9 Album is Dark Side of the Moon
2021-10-18 11:42:48.980 D/MEDIAINFO: ID = 4 SongId = 102 Title = Time track# = 10 Album is Dark Side of the Moon
2021-10-18 11:42:48.980 D/MEDIAINFO: EXTRACT 8 - TrackNumber descending
2021-10-18 11:42:48.984 D/MEDIAINFO: ID = 4 SongId = 102 Title = Time track# = 10 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 5 SongId = 97 Title = The Great Gig in the Sky track# = 9 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 6 SongId = 101 Title = Money track# = 8 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 7 SongId = 103 Title = Us and Them track# = 7 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 9 SongId = 104 Title = Brain Damage track# = 6 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 1 SongId = 100 Title = Breathe track# = 5 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 2 SongId = 99 Title = Speak to Me track# = 4 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 3 SongId = 98 Title = On the Run track# = 3 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 10 SongId = 95 Title = Eclipse track# = 2 Album is Dark Side of the Moon
2021-10-18 11:42:48.985 D/MEDIAINFO: ID = 8 SongId = 96 Title = Any Colour You Like track# = 1 Album is Dark Side of the Moon
    • 最后一行dao.getSortedMediaListV2("not a known column", true); 由于列名不正确而失败（上一行没有失败，但由于传递的列名不正确，结果的顺序可能与预期不符）。例外（如预期）是

    :-

    2021-10-18 11:42:48.989 E/SQLiteLog: (1) near "known": syntax error
2021-10-18 11:42:48.989 D/AndroidRuntime: Shutting down VM
2021-10-18 11:42:48.992 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: a.a.so69602045javaroomsortbycolumnsviacase, PID: 17538
    java.lang.RuntimeException: Unable to start activity ComponentInfo{a.a.so69602045javaroomsortbycolumnsviacase/a.a.so69602045javaroomsortbycolumnsviacase.MainActivity}: android.database.sqlite.SQLiteException: near "known": syntax error (code 1 SQLITE_ERROR): , while compiling: SELECT * FROM mediaentity ORDER BY not a known column ASC
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)

    附加

    第三种方法是通过选择适当的 Dao 的方法（可能在 @Dao 类中，如下例所示）调用各个 Dao，例如:-

    /* Method 3 */
@Query("SELECT * FROM mediaentity ORDER BY _id ASC")
abstract List<MediaEntity> getALlOrderBy_Id_ASC();
@Query("SELECT * FROM mediaentity ORDER BY _id DESC")
abstract List<MediaEntity> getALlOrderBy_Id_DESC();

@Query("SELECT * FROM mediaentity ORDER BY _SongId ASC")
abstract List<MediaEntity> getALlOrderBy_SongId_ASC();
@Query("SELECT * FROM mediaentity ORDER BY _SongId DESC")
abstract List<MediaEntity> getALlOrderBy_SongId_DESC();

@Query("SELECT * FROM mediaentity ORDER BY _title ASC")
abstract List<MediaEntity> getALlOrderBy_title_ASC();
@Query("SELECT * FROM mediaentity ORDER BY _title DESC")
abstract List<MediaEntity> getALlOrderBy_title_DESC();

@Query("SELECT * FROM mediaentity ORDER BY _trackNumber ASC")
abstract List<MediaEntity> getALlOrderBy_trackNumber_ASC();
@Query("SELECT * FROM mediaentity ORDER BY _trackNumber  DESC")
abstract List<MediaEntity> getALlOrderBy_trackNumber_DESC();

/* and so on */

public List<MediaEntity> getSortedMediaListV3(String sortbyColumn, boolean sortDirection) {
    List<MediaEntity> rv = new ArrayList(){};
    if (sortDirection) {
        switch ( sortbyColumn) {
            case "_Id":
                rv = getALlOrderBy_Id_ASC();
                break;
            case "_SongId":
                rv = getALlOrderBy_SongId_ASC();
                break;
            case "_title":
                rv = getALlOrderBy_title_ASC();
                break;
            case "_trackNumber":
                return getALlOrderBy_trackNumber_ASC();
        }
    } else {
        switch (sortbyColumn) {
            case "_Id":
                rv = getALlOrderBy_Id_DESC();
                break;
            case "_SongId":
                rv = getALlOrderBy_SongId_DESC();
                break;
            case "_title":
                rv = getALlOrderBy_title_DESC();
                break;
            case "_trackNumber":
                rv = getALlOrderBy_trackNumber_DESC();
        }
    }
    return rv;
}

    【讨论】：

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