Database update without data loss - sqlite

Question

there is a table with 3 columns: id, title, poem, favorite.
So, the favorite is written 1 or 0, the default is 0, it changes if the user adds a line to the Favorites.
The problem is that if I update the database (add more rows), all Favorites will disappear from the user. How to transfer the Favorites from the old database to the new one in the onUpgrade method?
DbHelper Class Code
public class PoemsDbHelper extends SQLiteOpenHelper {
private static String DB_NAME = "brodsky.db";
private static String DB_PATH = "";
private static final int DB_VERSION = 3;
private SQLiteDatabase db;
private final Context context;
private boolean needUpdate = false;
public PoemsDbHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
if (android.os.Build.VERSION.SDK_INT >= 17)
DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
else
DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
this.context = context;
copyDataBase();
this.getReadableDatabase();
}
public void updateDataBase() throws IOException {
if (needUpdate) {
File dbFile = new File(DB_PATH + DB_NAME);
if (dbFile.exists())
dbFile.delete();
copyDataBase();
needUpdate = false;
}
}
private boolean checkDataBase() {
File dbFile = new File(DB_PATH + DB_NAME);
return dbFile.exists();
}
private void copyDataBase() {
if (!checkDataBase()) {
this.getReadableDatabase();
this.close();
try {
copyDBFile();
} catch (IOException mIOException) {
throw new Error("ErrorCopyingDataBase");
}
}
}
private void copyDBFile() throws IOException {
InputStream input = context.getAssets().open(DB_NAME);
//InputStream input = context.getResources().openRawResource(R.raw.info);
OutputStream output = new FileOutputStream(DB_PATH + DB_NAME);
byte[] buffer = new byte[1024];
int length;
while ((length = input.read(buffer)) > 0)
output.write(buffer, 0, length);
output.flush();
output.close();
input.close();
}
public boolean openDataBase() throws SQLException {
db = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.CREATE_IF_NECESSARY);
return db != null;
}
#Override
public synchronized void close() {
if (db != null)
db.close();
super.close();
}
#Override
public void onCreate(SQLiteDatabase db) {
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (newVersion > oldVersion)
needUpdate = true;
}
}

Answer 1

In this case it seems you are overwriting your "old" database with a new, clean, empty database. I suggest trying copying the old database file to a temporary backup, overwrite old database file with new, clean, empty database file.
Then you must define an upgrade strategy, i.e. how are fields moved from v. 1 to v. 2. What happens if you removed a field? What happens if you added a new field? Has some of your data been restructured? This is an exercise that is best sketched out on paper.
You can now attach the old, backed up database to the new, clean database (see SQL command ATTACH), and insert new records into the new database from the old, following the strategy you sketched out above.
If anything fails, you can always revert to your backup file and notify the user, instead of loosing all their data.