Parse Server - How to lookup and replace a field of a query with field from another table in a single query

Question

I could not find a solution on Parse Server for the below issue. It is equivalent to using JOIN in SQL but because Parse Server uses NoSQL, the solution is not join.

Issue ; Reporting screen displays results of a query. But one of the field needs to be looked up from another class and replaced with a field in that other class.

I can only solve this issue by having two separate nested queries but this is way from efficient. Can you please show me how to do the following in a single query or more efficiently ;

 //get query result from database
        ParseQuery<ParseObject> query = ParseQuery.getQuery("access");
        query.whereStartsWith("tokenid", "prefix");
        query.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> objects, ParseException e) {
               for (int i=0; i<objects.size(); i++) {
                   String reportField1 = objects.get(i).getString("name");
                   String lookup = objects.get(i).getString("cityID");

                   //start the second query
                   ParseQuery<ParseObject> query2 = ParseQuery.getQuery("cities");
                   query2.whereEqualTo("cityID", lookup);
                   query2.getFirstInBackground(new GetCallback<ParseObject>() {
                       @Override
                       public void done(ParseObject object, ParseException e) {
                           String reportField2 = object.getString("cityname");
                       }
                   });
               }
            }
        });

Answer 1

What you're looking for is called pointer in Parse. Instead of storing cityID on your access object, store a pointer to a cities object and include it in your query.

Here is an example from the Android guide

ParseQuery<ParseObject> query = ParseQuery.getQuery("Comment");

// Retrieve the most recent ones
query.orderByDescending("createdAt");

// Only retrieve the last ten
query.setLimit(10);

// Include the post data with each comment
query.include("post");

query.findInBackground(new FindCallback<ParseObject>() {
  public void done(List<ParseObject> commentList, ParseException e) {
    // commentList now contains the last ten comments, and the "post"
    // field has been populated. For example:
    for (ParseObject comment : commentList) {
      // This does not require a network access.
      ParseObject post = comment.getParseObject("post");
      Log.d("post", "retrieved a related post");
    }
  }
});

By storing a pointer on your access object, you can get the corresponding cities object simply by including it in your query.