英文:
New to Parse Platform: Question on getting objectId of a relation
问题
我有以下的表格：
- 餐厅 (Restaurants)
- 桌子 (Table)
- 预约 (Reservation)
我正在为一个餐厅创建一个桌子的可用性搜索功能，用户需要输入日期和时间。搜索结果会显示在所选日期/时间可用的桌子，即在该时间之前没有被预订的桌子。
- 我在特定餐厅检查桌子的日期/时间：
- 这个 objectID 是从之前的活动 (餐厅概况) 传递过来的。
ParseQuery<ParseObject> restaurant = ParseQuery.getQuery("Restaurants");restaurant.get(objectID);
- 我从 "Table" 表中获取与餐厅关联的桌子：
ParseQuery<ParseObject> tableQuery = ParseQuery.getQuery("Table");tableQuery.whereMatchesQuery("restaurant_id", restaurant);
- 然后我从 "Reservation" 表中获取与这些桌子关联的预约，并将它们收集在
reservationResults列表中：
ParseQuery<ParseObject> reservations = ParseQuery.getQuery("Reservation");reservations.whereMatchesQuery("table_id", tableQuery);reservations.include("table_id");List<ParseObject> reservationResults = reservations.find();
- 从这里开始，我尝试遍历
ParseObject的列表，并在预约的日期/时间上进行一些计算和检查。如果开始选择的日期/时间与任何已经预约的日期/时间发生冲突，那么我会获取这些冲突的桌子的 objectId，并将它们添加到一个名为tableListToExclude的列表中。然后，这个列表会用于在 recyclerView 中检查是否不显示为所选时间预订的特定桌子。
for(int i = 0; i < reservationResults.size(); i++) {Date reservationDateTime = reservationResults.get(i).getDate("time");ParseObject reservation = reservationResults.get(i);ParseObject table = reservation.getParseObject("table_id");String tableId = table.getObjectId();Log.i(TAG, "|||||||||||TEST|||||||| ------> " + tableId);// 计算预约的两小时窗口Calendar calRes = Calendar.getInstance();assert reservationDateTime != null;calRes.setTime(reservationDateTime);calRes.add(Calendar.HOUR_OF_DAY, 2);// 设置两小时窗口的结束时间Date reservationEndTime = calRes.getTime();// 计算所选时间的两小时窗口Calendar calSelected = Calendar.getInstance();calSelected.setTime(combinedSelectedDate);calSelected.add(Calendar.HOUR_OF_DAY, 2);// 设置所选时间的结束时间Date selectedEndTime = calSelected.getTime();// 将所选日期/时间及其两小时窗口与预约表中的时间进行比较if((combinedSelectedDate.after(reservationDateTime) && combinedSelectedDate.before(reservationEndTime)) || (selectedEndTime.after(reservationDateTime) && selectedEndTime.before(reservationEndTime))) {Log.i(TAG, "||||||||||||TEST||||||||||||| ---------> Some dates fall in the 2 hour window");tableListToExclude.add(tableId);System.out.println(Arrays.asList(tableListToExclude));}}
在 logcat 中的错误：
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.parse.ParseObject.getObjectId()' on a null object reference
我被卡在这里，但我相信这只是因为我没有完全理解 Parse 以及如何查询关系或指针等等。我是否需要在这里创建另一个查询？还是以某种方式获取 ParseRelation，然后将其转换为 ParseObject，然后获取 objectId？我在这里尝试了一些不同的场景，但都没有成功，我认为我已经很接近了，但是还有一些我没有完全理解或者遗漏的东西...
另外，如果对于基于日期/时间来筛选 RecyclerView 项有更好的方法，也欢迎提出建议！如果需要更多的代码或者说明，请随时告诉我。谢谢！
英文:
I have the following tables
- Restaurants
- Table
- Reservation
I am creating a table availability search for a restaurant where the user inputs date and time. The result shows tables that are available AKA not already reserved at the selected date/time.
- I am checking the date/time for tables at a specific restaurant:
- this objectID is passed from the previous activity (Restaurant profile)
ParseQuery<ParseObject> restaurant = ParseQuery.getQuery("Restaurants");restaurant.get(objectID);
- I get the tables associated with the Restaurant from the Table table
ParseQuery<ParseObject> tableQuery = ParseQuery.getQuery("Table");tableQuery.whereMatchesQuery("restaurant_id", restaurant);
- Then I get the reservations associated with those tables on the Reservation table and collect them in the reservationResults list
ParseQuery<ParseObject> reservations = ParseQuery.getQuery("Reservation");reservations.whereMatchesQuery("table_id", tableQuery);reservations.include("table_id");List<ParseObject> reservationResults = reservations.find();
- From here I try to loop through the list of ParseObjects and do some calculations/checks on the reservation date/times. IF the date/time selected at the start clashes with any of the already made reservation date/times --> THEN I grab the table objectId of those that clash and add them to a 'List tableListToExclude'. This list is then used to check that certain tables aren't shown in a recyclerView if they are reserved for the selected time
for(int i = 0; i < reservationResults.size(); i++) {Date reservationDateTime = reservationResults.get(i).getDate("time");ParseObject reservation = reservationResults.get(i);ParseObject table = reservation.getParseObject("table_id");String tableId = table.getObjectId();Log.i(TAG, "|||||||||||TEST|||||||| ------> " + tableId);// calculates the two hour window of the reservationCalendar calRes = Calendar.getInstance();assert reservationDateTime != null;calRes.setTime(reservationDateTime);calRes.add(Calendar.HOUR_OF_DAY, 2);//sets the end time of two hour windowDate reservationEndTime = calRes.getTime();// calculates two hours window of selected timeCalendar calSelected = Calendar.getInstance();calSelected.setTime(combinedSelectedDate);calSelected.add(Calendar.HOUR_OF_DAY, 2);// sets the end time of the selectedDate selectedEndTime = calSelected.getTime();//compares the selected date/time and it's 2 hour window against the Reservation tableif((combinedSelectedDate.after(reservationDateTime) && combinedSelectedDate.before(reservationEndTime)) || (selectedEndTime.after(reservationDateTime) && selectedEndTime.before(reservationEndTime))) {Log.i(TAG, "||||||||||||TEST||||||||||||| ---------> Some dates fall in the 2 hour window");tableListToExclude.add(tableId);System.out.println(Arrays.asList(tableListToExclude));}}
The error I get in the logcat:
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.parse.ParseObject.getObjectId()' on a null object reference
I'm stuck here but I believe it's just from not totally understanding Parse and how to query relationships or pointers etc,... Do I need to create another query here? Or somehow get the ParseRelation and then that into a ParsObject and then get the objectId? I have tried a few different scenarios here but no luck, I think I am close but there's just something I'm not fully understanding or missing...
Also, any suggestions on a better approach to filter out my recyclerview items based on a date/time is welcome too!! If you need any more code or clarification just let me know. Thanks!
EDIT
Current version I have made tweaks to the queries at the start and also used findInBackground() instead of find():
// ParseQuery<ParseObject> restaurant = ParseQuery.getQuery("Restaurants");// restaurant.get(objectID);ParseQuery<ParseObject> tableQuery = ParseQuery.getQuery("Table");tableQuery.whereEqualTo("restaurant_id", ParseObject.createWithoutData("Restaurants", objectID));ParseQuery<ParseObject> reservations = ParseQuery.getQuery("Reservation");reservations.whereMatchesQuery("table_id", tableQuery);reservations.include("table_id");reservations.findInBackground(new FindCallback<ParseObject>() {@Overridepublic void done(List<ParseObject> reservationResults, ParseException e) {for(int i = 0; i < reservationResults.size(); i++) {Date reservationDateTime = reservationResults.get(i).getDate("time");ParseObject reservation = reservationResults.get(i);ParseObject table = reservation.getParseObject("table_id");String tableId = table.getObjectId();System.out.println(tableId);// calculates the two hour window of the reservationCalendar calRes = Calendar.getInstance();assert reservationDateTime != null;calRes.setTime(reservationDateTime);calRes.add(Calendar.HOUR_OF_DAY, 2);//sets the end time of two hour windowDate reservationEndTime = calRes.getTime();// calculates two hours window of selected timeCalendar calSelected = Calendar.getInstance();calSelected.setTime(combinedSelectedDate);calSelected.add(Calendar.HOUR_OF_DAY, 2);// sets the end time of the selectedDate selectedEndTime = calSelected.getTime();//compares the selected date and time against the reservation times of the tablesif((combinedSelectedDate.after(reservationDateTime) && combinedSelectedDate.before(reservationEndTime)) || (selectedEndTime.after(reservationDateTime) && selectedEndTime.before(reservationEndTime))) {Log.i(TAG, "||||||||||||TEST||||||||||||| ---------> Some dates fall in the 2 hour window");tableListToExclude.add(tableId);System.out.println(Arrays.asList(tableListToExclude));}}}});
答案1
得分: 1
尝试以下步骤1-3的代码：
ParseQuery<ParseObject> tableQuery = ParseQuery.getQuery("Table");tableQuery.whereEqualTo("restaurant_id", ParseObject.createWithoutData("Restaurants", objectID));ParseQuery<ParseObject> reservations = ParseQuery.getQuery("Reservation");reservations.whereMatchesQuery("table_id", tableQuery);reservations.include("table_id");List<ParseObject> reservationResults = reservations.find();
现在步骤4应该可以工作。请注意，您正在使用find函数，它会阻塞主线程。建议您在应用程序中使用findInBackground以获得更好的性能。
英文:
Try this for steps 1-3:
ParseQuery<ParseObject> tableQuery = ParseQuery.getQuery("Table");tableQuery.whereEqualTo("restaurant_id", ParseObject.createWithoutData("Restaurants", objectID));ParseQuery<ParseObject> reservations = ParseQuery.getQuery("Reservation");reservations.whereMatchesQuery("table_id", tableQuery);reservations.include("table_id");List<ParseObject> reservationResults = reservations.find();
Now step 4 should work. Note that you are using find function and it blocks the main thread. So it is recommended to use findInBackground for a better performance on your app.
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