GreenDao version change

I am using GreenDAO in my android project. I see a problem in GreenDAO. whenever I make changes to the existing tables and change the version to migrate the changes, GreenDAOis deleting all the tables. I tried to make changes in the GreenDAOgenerated files but it is not going to be the correct procedure and it did not work, however.

@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
  Log.i("greenDAO", "Upgrading schema from version " + oldVersion + " to " + newVersion + " by dropping all tables");
  dropAllTables(db, true);
  onCreate(db);
}

I tried to comment dropAllTables in above code it did not work, the code is regenerating on running the code? Does anybody know how to fix it?

EDIT:
I saw few questions related to this problem but they are OLD threads did not help me.

You can extend DaoMaster.DevOpenHelper and provide your own implementation of onUpgrade.

Implement your own DevOpenHelper

public class MyOpenHelper extends DaoMaster.DevOpenHelper {

    //..
    //override the constructor here by calling super
    //..

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        switch(oldVersion) {
        case 1:
            //upgrade logic from version 1 to 2
            /* break was omitted by purpose. */
        case 2:
            //upgrade logic from version 2 to 3
            /* break was omitted by purpose. */
        case 3:
            //upgrade logic from version 3 to 4
            break;
        default:
            throw new IllegalStateException(
                    "unknown oldVersion " + oldVersion);
        }
    }
}

Instantiate your class

DaoMaster.DevOpenHelper helper = new MyOpenHelper(this, databaseName, null);
SQLiteDatabase db = helper.getWritableDatabase();
DaoMaster daoMaster = new DaoMaster(db);

For more details, checkout how I did it here.