更新apk版本后删除了Android Sqlite数据库记录

Question

I have tried to implement the persistence layer of my application so that after updating the apk via Google Play, the database record can be maintained. When it comes ti the implementation, it erases all data after updating my apk version. Would you please tell me the way to back up and restore the sqlite records?

The below is my code

 private static final String DATABASE_NAME = "hkgadddlden.sqlite";

    private static final int DATABASE_VERSION = 6;

    private Dao<History, Integer> hDao = null;
    private Dao<Favourite, Integer> fDao = null;
    private Dao<Lm, Integer> lDao = null;
    private Dao<iconPlus, Integer> iDao = null;


    public DatabaseHelper(Context context)
    {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase database,ConnectionSource connectionSource)
    {
//      database.execSQL("create table history(t_id integer, topic text, page integer, PRIMARY KEY(t_id));");
//      database.execSQL("create table lm(t_id integer, PRIMARY KEY(t_id));");
//      database.execSQL("create table favourites(t_id integer, PRIMARY KEY(t_id));");

        try
        {
            TableUtils.createTable(connectionSource, History.class);
            TableUtils.createTable(connectionSource, Favourite.class);
            TableUtils.createTable(connectionSource, Lm.class); 
            TableUtils.createTable(connectionSource, iconPlus.class);            
        }
        catch (SQLException e)
        {
            Log.e(DatabaseHelper.class.getName(), "Can't create database", e);
            throw new RuntimeException(e);
        }
        catch (java.sql.SQLException e)
        {
            e.printStackTrace();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db,ConnectionSource connectionSource, int oldVersion, int newVersion)
    {
        db.execSQL("DROP TABLE IF EXISTS history"); //刪除舊有的資料表
        db.execSQL("DROP TABLE IF EXISTS lm");
        db.execSQL("DROP TABLE IF EXISTS favourite");
        db.execSQL("DROP TABLE IF EXISTS iconPlus");        
        onCreate(db, connectionSource);

        try
        {
            List<String> allSql = new ArrayList<String>();
            for (String sql : allSql)
            {
                db.execSQL(sql);
            }
        }
        catch (SQLException e)
        {
            Log.e(DatabaseHelper.class.getName(), "exception during onUpgrade", e);
            throw new RuntimeException(e);
        }

    }

Answer 1

Your onUpgrade function is dropping all the tables. That means you'll drop all the data. If you want to not drop them, you have to write alter statements for each possible upgrade instead.

Answer 2

You just have to use a check if you are upgrading your database version

public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
 if (oldVersion<2) {
// do upgrade from 1 to 2
 }

 if (oldVersion<3) {
// do upgrade from 2 to 3, which will also cover 1->3,
// since you just upgraded 1->2
 }

// and so on
 }

as you are writing this code in your db

    db.execSQL("DROP TABLE IF EXISTS history"); //刪除舊有的資料表
    db.execSQL("DROP TABLE IF EXISTS lm");
    db.execSQL("DROP TABLE IF EXISTS favourite");
    db.execSQL("DROP TABLE IF EXISTS iconPlus");        

it drops your table and data