java - 无法使用查询从解析数据库中检索字符串

Question

我正在尝试从解析对象中检索信息，但我将它们存储在其中的字符串始终等于 null。

这是我保存对象的方式

        // get current user
        ParseObject studentClasses = new ParseObject("StudentClasses");

        // register their periods into database
        studentClasses.put("student_id", ParseUser.getCurrentUser());
        studentClasses.put("first_period", ClassSelected_Period[PERIOD1]);
        studentClasses.put("second_period", ClassSelected_Period[PERIOD2]);
        studentClasses.put("third_period", ClassSelected_Period[PERIOD3]);
        studentClasses.put("fourth_period", ClassSelected_Period[PERIOD4]);
        studentClasses.put("fifth_period", ClassSelected_Period[PERIOD5]);
        studentClasses.put("sixth_period", ClassSelected_Period[PERIOD6]);
        studentClasses.put("seventh_period", ClassSelected_Period[PERIOD7]);

        // save the information into database
        studentClasses.saveInBackground();

它完美地保存了我的数据库。 student_id 是指向用户的指针，其余列是字符串。

我想检索所有这些字符串并将它们放入一个数组中，当我查询解析它们时它不起作用

这是我的问题

        // check if a user is not cached
        ParseUser currentUser = ParseUser.getCurrentUser();
        if (currentUser == null)
        {
            // prompt user to Register screen
            // create intent to start activity
            Intent intent = new Intent(MainActivity.this, RegisterActivity.class);
            intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

            // start new activity
            startActivity(intent);

            // stop current activity
            finish();
        }

        // query database for user's classes
        ParseQuery<ParseObject> query = ParseQuery.getQuery("StudentClasses");
        query.whereEqualTo("student_id", ParseUser.getCurrentUser());

        query.getFirstInBackground(new GetCallback<ParseObject>()
        {
            @Override
            public void done (ParseObject parseObject, ParseException e)
            {
                if (e == null)
                {
                    // retrieved the object
                    userClasses[PERIOD1] = parseObject.getString("first_period");
                    userClasses[PERIOD2] = parseObject.getString("second_period");
                    userClasses[PERIOD3] = parseObject.getString("third_period");
                    userClasses[PERIOD4] = parseObject.getString("fourth_period");
                    userClasses[PERIOD5] = parseObject.getString("fifth_period");
                    userClasses[PERIOD6] = parseObject.getString("sixth_period");
                    userClasses[PERIOD7] = parseObject.getString("seventh_period");
                }
                else
                {
                    // failed lookup. Do something here
                    Toast.makeText(getApplicationContext(),"Exception Thrown" ,Toast.LENGTH_SHORT).show();
                }
            }
        });

我查看了解析文档，它看起来应该可以工作，但它不保存字符串

感谢任何帮助或意见，谢谢!

编辑:我为查询部分展示了更多代码以显示当前用户

Answer 1

这里我假设，您的解析数据库中存储了数据..并且它工作正常..所以要检索它请尝试以下..

 ParseQuery<ParseObject> query = ParseQuery.getQuery("StudentClasses");
    query.whereEqualTo("student_id", ParseUser.getCurrentUser());

    query.findInBackground(new FindCallback<ParseObject>()
    {
        @Override
        public void done (List<ParseObject> list, ParseException e)
        {
            if (e == null)
            {
               for(int i=0; i < list.size(); i++) {
                userClasses[PERIOD1] = list.get(i).getString("first_period");
                userClasses[PERIOD2] = list.get(i).getString("second_period");
                userClasses[PERIOD3] = list.get(i).getString("third_period");
                userClasses[PERIOD4] = list.get(i).getString("fourth_period");
                userClasses[PERIOD5] = list.get(i).getString("fifth_period");
                userClasses[PERIOD6] = list.get(i).getString("sixth_period");
                userClasses[PERIOD7] = list.get(i).getString("seventh_period");
               }
            }
            else
            {
              Toast.makeText(getApplicationContext(),"Exception Thrown" ,Toast.LENGTH_SHORT).show();
            }
        }
    });

希望对您有所帮助!