记录不会从SQLite数据库中删除

Question

I'm currently working on my A Level Computer Science Controlled Assessment, making a Scout Manager application in Android Studio, Java and XML, none of which I have used before. I'm now on the last stretch, but I've run into an error which I can't seem to solve.

I'm trying to delete a session record from the events table. This has worked perfectly fine before, however for some reason, despite no change in code (that I can remember, anyway), it no longer does.

Here is the code from the "Edit Event" activity:

//Deletes the event from the database
    public void deleteEvent(View view)
    {
        boolean result=DatabaseHandler.deleteSession(sessionid);
        if (result==true)
        {
            Toast.makeText(
                    context,
                    "Event Deleted",
                    Toast.LENGTH_SHORT
            ).show();
            backToProgramme(view);
        }
        else
        {
            Toast.makeText(
                    context,
                    "Error - please try again",
                    Toast.LENGTH_SHORT
            ).show();
        }
    }

And here is the code from the databaseHandler:

//Deleting a session in the events table
    public boolean deleteSession(int id)
    {
        boolean result = false;
        String query = "SELECT * FROM " + TABLE_EVENTS + " WHERE " + COLUMN_SEID + " = '"
                + String.valueOf(id) + "'";
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query, null);
        sessionDetails session = new sessionDetails();
        if (cursor.moveToFirst())
        {
            session.setSessionID(Integer.parseInt(cursor.getString(0)));
            db.delete (TABLE_EVENTS, COLUMN_SCID + "=?", new String[]{String.valueOf(
                    session.getSessionID())});
            cursor.close();
            result = true;
        }
        return result;
    }

I can't at all work out why this isn't deleting the record.

Answer 1

What you are doing here is:
search the table TABLE_EVENTS to find a row with COLUMN_SEID = id and if found then get the value of column COLUMN_SCID and delete the row where COLUMN_SCID equals that value!
Why all this?
Can't you just delete the row with COLUMN_SEID = id ?
I believe that your code should be written like this:

public boolean deleteSession(int id) {
    SQLiteDatabase db = this.getWritableDatabase();
    return db.delete(TABLE_EVENTS, COLUMN_SEID + " = ?", new String[]{String.valueOf(id)}) > 0;
}

The method delete() returns the number of deleted rows, so deleteSession() will return false if no row was deleted.