在解析中查询一对多关系

Question

Hello im trying to query a one to many relationship in parse. I have an Event table and invitation Table. An event has many invitations and many invitations are created by an event. The Event table has a column called status . Status has a value of 1 which means the owner has. In invitation table i have a column also called status and others users if going to an event will update the status to 1. I was successful in creating the table. Now i am trying to attempt to query both Event and Invitation table where the status is 1 . But i am having trouble accomplishing this task. Below is my code:

 ParseQuery<ParseObject> query = ParseQuery.getQuery("Event");
        // Restrict to cases where the author is the current user.
        //pass in a ParseUser and not String of that user

        query.whereEqualTo("author", ParseUser.getCurrentUser());
        query.whereEqualTo("Status", "1");
        query.include("EventTitle");

        ParseQuery<ParseObject> parseQuery = ParseQuery.getQuery("Invitation");
        parseQuery.whereMatchesQuery("EventId", query);


      //  query.orderByAscending("createAt");

        // Run the query
        parseQuery.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> objectList, ParseException e) {
                if (e == null) {
                    // If there are results, update the list of event and notify the adapter
                    Log.d(TAG, "Im in background");
                  //  eventList.clear();
                    invitationList.clear();
                    for (ParseObject event : objectList) {
                        invitationList.add((Invitation)event);
                    }
                    Log.d(TAG, String.valueOf(invitationList.size()));

                    updateEventsList();

                } else {
                    Log.d(TAG, "Event retrieval error: " + e.getMessage());
                }
            }
        });
    }

And when i try to display in a ListView:

TextView tvTitle = (TextView)convertView.findViewById(R.id.textView_eventTitle);

Error: i get a null pointer indicating a fetch Might be needed. Please what i'm doing wrong

Answer 1

I believe you might have two options:

 ParseQuery<ParseObject> query = ParseQuery.getQuery("Event");
 query.whereEqualTo("author", ParseUser.getCurrentUser());
 query.whereEqualTo("Status", "1");


ParseQuery<ParseObject> parseQuery = ParseQuery.getQuery("Invitation");
parseQuery.whereEqualTo("EventId", id)

List<ParseQuery<ParseObject>> queries = new ArrayList<ParseQuery<ParseObject>>();
queries.add(query);
queries.add(parseQuery);

ParseQuery<ParseObject> mainQuery = ParseQuery.or(queries);
mainQuery.findInBackground(new FindCallback<ParseObject>() {
  public void done(List<ParseObject> results, ParseException e) {
    // results has the list of of invitations/events.
  }
});

You can also try and save the eventId to the invitations table, that way you will not have to query two tables. That will however, duplicate some data, which you may or may not be okay with.