Question

I want to upgrade the database to a newer version. How would i go about doing that in the Upgrade method it gives you?

 private static final String DATABASE_NAME = " nba";
private static final String DATABASE_TABLE = "bookList";
private static final int DATABASE_VERSION = 1;
private static String TAG = "Upgrading Database!";
public static final String KEY_BOOK = "book";
public static final String KEY_AUTHOR = "author";
public static final String KEY_ISBN = "isbn";
public static final String KEY_ROWID = "_id";
public static final String KEY_RATING = "rating";
public static final String KEY_STATUS = "status";

private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;


private static final String DATABASE_CREATE = 
        " create table " +  DATABASE_TABLE  + " ("
        + KEY_ROWID + " integer primary key autoincrement,  "
        + KEY_AUTHOR + " text not null, "
        + KEY_BOOK + " text not null, "
        + KEY_RATING + " text not null, "
        + KEY_STATUS + " text not null, "
        + KEY_ISBN + " text not null); ";

private final Context mCtx;


public DbAdapter (Context ctx){
    this.mCtx = ctx;



        }

        private static class DatabaseHelper extends SQLiteOpenHelper{
        DatabaseHelper(Context context){
            super(context, DATABASE_NAME, null, DATABASE_VERSION);


        }

        @Override
        public void onCreate(SQLiteDatabase db) {
        db.execSQL(DATABASE_CREATE);


        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
              Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                        + newVersion + ", which will destroy all old data");
                db.execSQL("DROP TABLE IF EXISTS user");
                db.execSQL("DROP TABLE IF EXISTS site");
                db.execSQL("DROP TABLE IF EXISTS site_user");
                db.execSQL("DROP TABLE IF EXISTS article");
                onCreate(db); 
    }
}
        public DbAdapter open() throws SQLException{

            mDbHelper =  new DatabaseHelper(mCtx);
            mDb = mDbHelper.getWritableDatabase();
            return this;
        }
        public void close(){
            mDbHelper.close();
        }

        public long createBook(String book, String author, String isbn, float rating, String status){
            ContentValues initialValues = new ContentValues();
            initialValues.put(KEY_BOOK, book);
            initialValues.put(KEY_AUTHOR, author);
            initialValues.put(KEY_ISBN, isbn);
            initialValues.put(KEY_RATING, rating);
            initialValues.put(KEY_STATUS, status);

            return mDb.insert(DATABASE_TABLE, null, initialValues);

        }
        public boolean deleteBook(long rowId){
            return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;

        }
        public Cursor fetchAllBooks(){          
            return mDb.query(DATABASE_TABLE, new String[]{KEY_BOOK, KEY_ISBN,KEY_AUTHOR,KEY_ROWID, KEY_RATING, KEY_STATUS}, null, null, null, null, null);
        }
        public Cursor fetchBook(long rowId) throws SQLException{
            Cursor mCursor = 
            mDb.query(DATABASE_TABLE, new String[]{KEY_BOOK, KEY_AUTHOR,KEY_ROWID, KEY_ISBN, KEY_RATING, KEY_STATUS}, KEY_ROWID + "=" +
                        rowId, null, null, null, null);

            if(mCursor != null){
                mCursor.moveToFirst();
            }
            return mCursor;

        }
        public boolean updateBook(long rowId, String book, String author, String isbn, float rating, String status){
            ContentValues args = new ContentValues();
            args.put(KEY_BOOK, book);
            args.put(KEY_AUTHOR, author);
            args.put(KEY_ISBN, isbn);
            args.put(KEY_RATING, rating);
            args.put(KEY_STATUS, status);

            return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null)> 0;


        }


}

Answer 1

There’s no “magic bullet” for upgrading a database. The strategy your current implementation is fine except it will blow away all of the users data. The most elegant, yet complex solution, would be to assign a version number to the database by creating a special table to hold that value. Then, based on the version, the onUpgrade method executes a series of alter statements to modify the structure to meet the new version. I would do it incrementally and iteratively so that each version only needs to know how to upgrade from the previous version.

That is to say, version 3 has no idea how to upgrade from version 1 to 2, but it does know how to upgrade from version 2 to 3. Or, if the new version is version 5 and you’re at version 1, you run the script to upgrade from 1 to 2, then 2 to 3, then 3 to 4 and finally from 4 to 5. Does that make sense?

If you’re asking about how to modify table structure in SQL, check out the ALTER TABLE statement.