在SQLite数据库中添加新列

Question

I am pretty new to Android development and I am trying to implement a database for my app. I started with only having one column in the database (COLUMN_DATE) and then added another column (COLUMN_REPEAT). This worked fine and printed the results as expected. However, when I tried adding another column (COLUMN_ACCOUNT), printDatabase() in MainActivity did not print anything. I understand you can view what is in your database by using Android Device Monitor, but I keep getting an error when I click on that so I cannot use it (That is a separate issue which I haven't been able to solve). Hence, I am unsure if it is just an issue with printing the database or if there is actually any data in the database at all. Any help would be much appreciated

----MainActivity.java----

dbHandler = new DatabaseHandler(this, null, null, 1);
printDatabase();

//Print the database
public void printDatabase() {
    String dbString = dbHandler.databaseToString();
    recordsTextView.setText(dbString);
}

//Add an item to the database
public void addButtonClicked(View view){
    Income date = new Income(dateView.getText().toString());
    Income repeat = new Income(repeatSpinner.getSelectedItem().toString());
    Income account = new Income(accountSpinner.getSelectedItem().toString());
    dbHandler.addData(date, repeat, account);
   printDatabase();
}

//Delete items with input date from database
public void deleteButtonClicked(View view){
    String inputText = dateView.getText().toString();
    dbHandler.deleteData(inputText);
    printDatabase();
}

----DatabaseHandler.java----

public class DatabaseHandler extends SQLiteOpenHelper{
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "IncomeExpenseDB.db";
public static final String TABLE_NAME = "income_expense";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_DATE = "date";
public static final String COLUMN_REPEAT = "repeat";
public static final String COLUMN_ACCOUNT = "account";

public DatabaseHandler(Context context, String name, 
SQLiteDatabase.CursorFactory factory, int version) {
    super(context, DATABASE_NAME, factory, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
    String query = "CREATE TABLE " + TABLE_NAME + "(" +
            COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
            COLUMN_DATE + " TEXT, " + COLUMN_REPEAT + " TEXT, " + 
            COLUMN_ACCOUNT + " TEXT " +
            ");";
    db.execSQL(query);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
    onCreate(db);
}

//Add a new row to the database
public void addData(Income date, Income repeat, Income 
account){
    ContentValues values = new ContentValues();
    values.put(COLUMN_DATE, date.get_item());
    values.put(COLUMN_REPEAT, repeat.get_item());
    values.put(COLUMN_ACCOUNT, account.get_item());
    SQLiteDatabase db = getWritableDatabase();
    db.insert(TABLE_NAME, null, values);
    db.close();
}


//Delete data from the database
public void deleteData(String date){
    SQLiteDatabase db = getWritableDatabase();
    db.execSQL("DELETE FROM " + TABLE_NAME + " WHERE " + COLUMN_DATE + "=\"" 
    + date + "\";");
}

// Create a string to print out in MainActivity
public String databaseToString() {
    String dbString = "";
    SQLiteDatabase db = getWritableDatabase();
    String query = "SELECT * FROM " + TABLE_NAME + " WHERE 1";
    //Cursor points to a location in results
    Cursor c = db.rawQuery(query, null);
    //Move to first row in results
    c.moveToFirst();
    while (!c.isAfterLast()) {
        if (c.getString(c.getColumnIndex("date")) != null && 
        c.getString(c.getColumnIndex("repeat")) != null && 
        c.getString(c.getColumnIndex("account")) != null) {
            dbString += c.getString(c.getColumnIndex("date"));
            dbString += " ";
            dbString += c.getString(c.getColumnIndex("repeat"));
            dbString += " ";
            dbString += c.getString(c.getColumnIndex("account"));
            dbString += "\n";
        }
        c.moveToNext();
    }
    db.close();
    return dbString;
}

}

----Income.java----

public class Income {
    private int _id;
    private String _item;

    public Income(){
    }
    public Income(String item) {
        this._item = item;
    }
    public int get_id() {
        return _id;
    }
    public void set_id(int _id) {
        this._id = _id;
    }
    public String get_item() {
        return _item;
    }
    public void set_item(String _item) {
        this._item = _item;
    }
}

Answer 1

Uninstalling and reinstalling is very naive approach which will only work in development phase. When your app goes on to play store, users are not going to uninstall and reinstall the app.

Correct way to update the database for published apps is to increase your db version and use onUpgrade method to update your database.

look at this method

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
    onCreate(db);
}

In current scenario if you just increase your db version, it will drop existing table and create a new one with new columns and specifications. The downside is that you'll lose all of your existing data.

If you want to save existing data and add new column to db, you have to do something like this -

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
  switch(oldVersion) {
    case 1:
      //add new column
      sqLiteDatabase.execSQL("ALTER TABLE "+ TABLE_NAME + " ADD COLUMN "+ NEW_COLUMN + " INTEGER/TEXT ");
  }
}

Answer 2

Just update your version of database when you add any column or make any update in the table. ... this helps me hope it will also work for you.