SQLite onUpgrade 删除和添加列

Question

在我的 Android 项目中，我有一张使用了一段时间的表格。现在我想删除一列'image_byte'并添加一个新的'image_path'。我不能只是在使用应用程序时重命名该列，它需要删除 image_byte 中的文本，以便不再使用它。

我实现了 SQLiteOpenHelper，下面的代码在 onUpgrade 中：

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
    //check if upgrade is really needed
    if(newVersion > oldVersion) {
        tableSQL = "CREATE TABLE IF NOT EXISTS table1 ( id INTEGER PRIMARY KEY, name TEXT, image_path TEXT)";

        db.execSQL(tableSQL);

        //get all the current tableName table columns
        List<String> columns = getColumns(db, "table1");

        //rename the old table
        db.execSQL("ALTER TABLE table1 RENAME TO temp_table1;");

        //create the new tableName table
        db.execSQL(tableSQL);

        //merge the old and new columns, keep all the old ones
        columns.retainAll(getColumns(db, "table1"));
        String cols = joinColumnNames(columns, ",");

        //insert the old data in the new table
        db.execSQL(String.format("INSERT INTO %s (%s) SELECT %s FROM temp_%s", "table1", cols, cols, "table1"));

        //delete the old temp table
        db.execSQL("DROP table 'temp_table1'");
    }
}

还有 getColumns 函数：

private List<String> getColumns(SQLiteDatabase db, String tableName){
    List<String> ar = null;
    Cursor c = null;
    try{
        c = db.rawQuery("SELECT * FROM " + tableName + " limit 1", null);
        if(c != null){
            ar = new ArrayList< >(Arrays.asList(c.getColumnNames()));
        }
    } catch (Exception e){

    } finally {
        if (c != null){
            c.close();
        }
    }
    return ar;
}

但在调试应用程序时，它说“image_byte”列不存在，并且无法将 temp_table1 中的内容复制到 table1。这是正确的，因为它现在是 'image_path' 并且不应复制 image_byte。但为什么 getColumns 会返回旧列？因为当我使用 Log.d 时，它会显示 'id'、'name'、'image_byte'。因此，retainAll 函数不会删除“image_byte”。我似乎无法弄清楚为什么它仍然返回 image_byte。这可能是愚蠢和简单的，但我只是不明白。

Answer 1

我认为问题很可能是由于 columns.retainAll(getColumns(db, "table1")); 似乎从原始 table1 中检索列而导致的缓存。

这是我进行的一些测试的结果：-

10-15 13:37:19.319 26740-26740/? D/DBINFO: onUpgrade Started.
10-15 13:37:19.320 26740-26740/? D/DBINFO: Databse info in onUpgrade after table rename to temp_table1
10-15 13:37:19.320 26740-26740/? D/SQLITE_CSU: DatabaseList Row 1 Name=main File=/data/data/mjt.sqlitedbexamples/databases/imagestore
10-15 13:37:19.320 26740-26740/? D/SQLITE_CSU: Database Version = 1
10-15 13:37:19.320 26740-26740/? D/SQLITE_CSU: Table Name = android_metadata Created Using = CREATE TABLE android_metadata (locale TEXT)
10-15 13:37:19.320 26740-26740/? D/SQLITE_CSU: Table = android_metadata ColumnName = locale ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 13:37:19.320 26740-26740/? D/SQLITE_CSU: Table Name = temp_table1 Created Using = CREATE TABLE "temp_table1"(id INTEGER PRIMARY KEY,name TEXT,image_byte TEXT)
10-15 13:37:19.320 26740-26740/? D/SQLITE_CSU: Table = temp_table1 ColumnName = id ColumnType = INTEGER Default Value = null PRIMARY KEY SEQUENCE = 1
10-15 13:37:19.320 26740-26740/? D/SQLITE_CSU: Table = temp_table1 ColumnName = name ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 13:37:19.320 26740-26740/? D/SQLITE_CSU: Table = temp_table1 ColumnName = image_byte ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 13:37:19.321 26740-26740/? D/DBINFO: Databse info in onUpgrade after creation of new table1.
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: DatabaseList Row 1 Name=main File=/data/data/mjt.sqlitedbexamples/databases/imagestore
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Database Version = 1
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table Name = android_metadata Created Using = CREATE TABLE android_metadata (locale TEXT)
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table = android_metadata ColumnName = locale ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table Name = temp_table1 Created Using = CREATE TABLE "temp_table1"(id INTEGER PRIMARY KEY,name TEXT,image_byte TEXT)
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table = temp_table1 ColumnName = id ColumnType = INTEGER Default Value = null PRIMARY KEY SEQUENCE = 1
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table = temp_table1 ColumnName = name ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table = temp_table1 ColumnName = image_byte ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table Name = table1 Created Using = CREATE TABLE table1(id INTEGER PRIMARY KEY, name TEXT,image_path TEXT)
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table = table1 ColumnName = id ColumnType = INTEGER Default Value = null PRIMARY KEY SEQUENCE = 1
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table = table1 ColumnName = name ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 13:37:19.321 26740-26740/? D/SQLITE_CSU: Table = table1 ColumnName = image_path ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 13:37:19.321 26740-26740/? D/ORIG COLUMNS: Orignal Column Info - Column=id Column=name Column=image_byte 
10-15 13:37:19.321 26740-26740/? D/NEWTAB COLUMNS: Columns from new table1 - Column=id Column=name Column=image_byte 
10-15 13:37:19.321 26740-26740/? D/RETAIN COLUMNS: Columns After Retain - Column=id Column=name Column=image_byte 
10-15 13:37:19.321 26740-26740/? D/JOINED COLUMNS: id,name,image_byte
10-15 13:37:19.321 26740-26740/? E/SQLiteLog: (1) table table1 has no column named image_byte
10-15 13:37:19.329 26740-26740/? D/AndroidRuntime: Shutting down VM

最后几行 D/ORIG COLUMNS、D/NEWTAB COLUMNS、D/RETAIN COLUMNS。 D/RETAIN COLUMNS 表示 image_byte 已被提取。

也许引入一个中间表名，然后最终将其重命名为原始表名可能会解决该问题。

请注意，SQLITE_CSU 输出是由提到的实用程序产生的 here。

这是用于测试/生成上述内容的 onUpgrade 代码：-

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldversion, int newversion) {
        String tableSQL = "CREATE TABLE IF NOT EXISTS " + TBNAME + "(" +
                "id INTEGER PRIMARY KEY, " +
                "name TEXT," +
                "image_path TEXT" +
                ")";
        if (newversion > oldversion) {
            Log.d("DBINFO","onUpgrade Started.");
            db.execSQL(tableSQL);

            //get all the current tableName table columns
            List<String> columns = getColumns(db, "table1");

            //rename the old table
            db.execSQL("ALTER TABLE table1 RENAME TO temp_table1;");
            Log.d("DBINFO","Databse info in onUpgrade after table rename to temp_table1");
            CommonSQLiteUtilities.logDatabaseInfo(db);

            //create the new tableName table
            db.execSQL(tableSQL);
            Log.d("DBINFO","Databse info in onUpgrade after creation of new table1.");
            CommonSQLiteUtilities.logDatabaseInfo(db);

            //merge the old and new columns, keep all the old ones
            String loginfo = "Orignal Column Info - ";
            for (String s:columns) {
                loginfo = loginfo + "Column=" + s + " ";
            }
            Log.d("ORIG COLUMNS",loginfo);
            loginfo = "Columns from new table1 - ";
            for (String s: getColumns(db, "table1")) {
                loginfo = loginfo + "Column=" + s + " ";
            }
            Log.d("NEWTAB COLUMNS",loginfo);
            columns.retainAll(getColumns(db, "table1"));
            loginfo = "Columns After Retain - ";
            for (String s: columns) {
                loginfo = loginfo + "Column=" + s + " ";
            }
            Log.d("RETAIN COLUMNS",loginfo);
            String cols = joinColumnNames(columns, ",");
            Log.d("JOINED COLUMNS",cols);

            //insert the old data in the new table
            db.execSQL(String.format("INSERT INTO %s (%s) SELECT %s FROM temp_%s", "table1", cols, cols, "table1"));

            //delete the old temp table
            db.execSQL("DROP table 'temp_table1'");
            Log.d("DBINFO","Databse info in onUpgrade after DELETING temp_table1.");
        }

---

工作示例：-

在此示例中，数据从原始表中提取到游标中，使用不同的名称创建新表，将数据加载到新表中，然后删除旧表，最后重命名新表。

这可能会稍微复杂一些，因为它维护 id，但它只有 1 行：-

cv.put("id",Long.toString(olddata.getLong(olddata.getColumnIndex("id"))));

注意！以//<<<<< 注释的行纯粹用于记录活动。虽然如果读取/遍历 olddata 游标（即将位置返回到第一行之前），则需要 olddata.moveToPosition(-1); //<<<<<。

@Override
public void onUpgrade(SQLiteDatabase db, int oldversion, int newversion) {

    String temptableSQL = "CREATE TABLE IF NOT EXISTS temp_" + TBNAME + "(" +
            "id INTEGER PRIMARY KEY, " +
            "name TEXT," +
            "image_path TEXT" +
            ")";
    if (newversion > oldversion) {
        Log.d("DBINFO","onUpgrade Started.");
        db.execSQL(temptableSQL);

        Cursor olddata = db.query(TBNAME,null,null,null,null,null,null);
        CommonSQLiteUtilities.logCursorData(olddata); //<<<<
        olddata.moveToPosition(-1); //<<<<<

        //db.execSQL(tableSQL);
        Log.d("DBINFO","Databse info in onUpgrade after creation of new table1.");
        CommonSQLiteUtilities.logDatabaseInfo(db); //<<<<<
        Log.d("DBCOPYDATA",
                "Copying data from OLD Data. # rows = " +  
                        Integer.toString(olddata.getCount())
        ); //<<<<<
        while (olddata.moveToNext()) {
            ContentValues cv = new ContentValues();
            Log.d("DBCOPYDATA","ROW " + Integer.toString(olddata.getPosition()) +
                    "\n\tID=" + Long.toString(olddata.getLong(olddata.getColumnIndex("id"))) +
                    "\n\tNAME=" + olddata.getString(olddata.getColumnIndex("name")) +
                    "\n\tIMG =" + olddata.getString(olddata.getColumnIndex("image_byte"))
            ); //<<<<<
            cv.put("id",Long.toString(olddata.getLong(olddata.getColumnIndex("id"))));
            cv.put("name",olddata.getString(olddata.getColumnIndex("name")));
            cv.put("image_path",olddata.getString(olddata.getColumnIndex("image_byte")));

            Long id = db.insert("temp_" + TBNAME,null,cv);
            Log.d("DBCOPYDATA","INSERTED ID=" + Long.toString(id)); //<<<<<

        }
        olddata.close();
        db.execSQL("DROP TABLE IF EXISTS " + TBNAME);
        db.execSQL("ALTER TABLE temp_" + TBNAME + " RENAME TO " + TBNAME);

        Cursor csr = db.query(TBNAME,null,null,null,null,null,null); //<<<<<
        CommonSQLiteUtilities.logDatabaseInfo(db); //<<<<<
        CommonSQLiteUtilities.logCursorData(csr); //<<<<<
        csr.close(); //<<<<<
    }
}

成功测试的输出：-

10-15 17:54:41.618 16960-16960/? D/DBINFO: onUpgrade Started.
10-15 17:54:41.619 16960-16960/? D/SQLITE_CSU: logCursorData Cursor has 3 rows with 3 columns.
10-15 17:54:41.619 16960-16960/? D/SQLITE_CSU: Information for row 1 offset=0
                                                For Column id Type is INTEGER value as String is 1 value as long is 1 value as double is 1.0
                                                For Column name Type is STRING value as String is Test001 value as long is 0 value as double is 0.0
                                                For Column image_byte Type is STRING value as String is mypath/mypath/images/image001 value as long is 0 value as double is 0.0
10-15 17:54:41.619 16960-16960/? D/SQLITE_CSU: Information for row 2 offset=1
                                                For Column id Type is INTEGER value as String is 2 value as long is 2 value as double is 2.0
                                                For Column name Type is STRING value as String is Test001 value as long is 0 value as double is 0.0
                                                For Column image_byte Type is STRING value as String is mypath/mypath/images/image002 value as long is 0 value as double is 0.0
10-15 17:54:41.619 16960-16960/? D/SQLITE_CSU: Information for row 3 offset=2
                                                For Column id Type is INTEGER value as String is 3 value as long is 3 value as double is 3.0
                                                For Column name Type is STRING value as String is Test001 value as long is 0 value as double is 0.0
                                                For Column image_byte Type is STRING value as String is mypath/mypath/images/image003 value as long is 0 value as double is 0.0
10-15 17:54:41.619 16960-16960/? D/DBINFO: Databse info in onUpgrade after creation of new table1.
10-15 17:54:41.619 16960-16960/? D/SQLITE_CSU: DatabaseList Row 1 Name=main File=/data/data/mjt.sqlitedbexamples/databases/imagestore
10-15 17:54:41.619 16960-16960/? D/SQLITE_CSU: Database Version = 1
10-15 17:54:41.619 16960-16960/? D/SQLITE_CSU: Table Name = android_metadata Created Using = CREATE TABLE android_metadata (locale TEXT)
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table = android_metadata ColumnName = locale ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table Name = table1 Created Using = CREATE TABLE table1(id INTEGER PRIMARY KEY,name TEXT,image_byte TEXT)
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table = table1 ColumnName = id ColumnType = INTEGER Default Value = null PRIMARY KEY SEQUENCE = 1
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table = table1 ColumnName = name ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table = table1 ColumnName = image_byte ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table Name = temp_table1 Created Using = CREATE TABLE temp_table1(id INTEGER PRIMARY KEY, name TEXT,image_path TEXT)
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table = temp_table1 ColumnName = id ColumnType = INTEGER Default Value = null PRIMARY KEY SEQUENCE = 1
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table = temp_table1 ColumnName = name ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 17:54:41.620 16960-16960/? D/SQLITE_CSU: Table = temp_table1 ColumnName = image_path ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 17:54:41.620 16960-16960/? D/DBCOPYDATA: Copying data from OLD Data. # rows = 3
10-15 17:54:41.620 16960-16960/? D/DBCOPYDATA: ROW 0
                                                ID=1
                                                NAME=Test001
                                                IMG =mypath/mypath/images/image001
10-15 17:54:41.620 16960-16960/? D/DBCOPYDATA: INSERTED ID=1
10-15 17:54:41.620 16960-16960/? D/DBCOPYDATA: ROW 1
                                                ID=2
                                                NAME=Test001
                                                IMG =mypath/mypath/images/image002
10-15 17:54:41.620 16960-16960/? D/DBCOPYDATA: INSERTED ID=2
10-15 17:54:41.620 16960-16960/? D/DBCOPYDATA: ROW 2
                                                ID=3
                                                NAME=Test001
                                                IMG =mypath/mypath/images/image003
10-15 17:54:41.620 16960-16960/? D/DBCOPYDATA: INSERTED ID=3
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: DatabaseList Row 1 Name=main File=/data/data/mjt.sqlitedbexamples/databases/imagestore
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Database Version = 1
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Table Name = android_metadata Created Using = CREATE TABLE android_metadata (locale TEXT)
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Table = android_metadata ColumnName = locale ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Table Name = table1 Created Using = CREATE TABLE "table1"(id INTEGER PRIMARY KEY, name TEXT,image_path TEXT)
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Table = table1 ColumnName = id ColumnType = INTEGER Default Value = null PRIMARY KEY SEQUENCE = 1
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Table = table1 ColumnName = name ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Table = table1 ColumnName = image_path ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: logCursorData Cursor has 3 rows with 3 columns.
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Information for row 1 offset=0
                                                For Column id Type is INTEGER value as String is 1 value as long is 1 value as double is 1.0
                                                For Column name Type is STRING value as String is Test001 value as long is 0 value as double is 0.0
                                                For Column image_byte Type is STRING value as String is mypath/mypath/images/image001 value as long is 0 value as double is 0.0
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Information for row 2 offset=1
                                                For Column id Type is INTEGER value as String is 2 value as long is 2 value as double is 2.0
                                                For Column name Type is STRING value as String is Test001 value as long is 0 value as double is 0.0
                                                For Column image_byte Type is STRING value as String is mypath/mypath/images/image002 value as long is 0 value as double is 0.0
10-15 17:54:41.621 16960-16960/? D/SQLITE_CSU: Information for row 3 offset=2
                                                For Column id Type is INTEGER value as String is 3 value as long is 3 value as double is 3.0
                                                For Column name Type is STRING value as String is Test001 value as long is 0 value as double is 0.0
                                                For Column image_byte Type is STRING value as String is mypath/mypath/images/image003 value as long is 0 value as double is 0.0