Compund Query with OR operator flutter and firebase

Question

I am creating a flutter app that should query a Firestore collection and return results if two conditions are met. Here is my code:

Stream<List<FormQuestions>> get question {
  return someCollection
  .where('myQUestion', isEqualTo: 'nameQuestion')
  .snapshots()
  .map(_someQuestionListFromSnapshot);
}

If I do with just one .where() condition, it works fine. But with two, it gives no results although I have documents that meet both conditions. I would like it to return for multiple .where() conditions like so:

Stream<List<FormQuestions>> get question {
  return someCollection
  .where('myQUestion', isEqualTo: 'nameQuestion')
  .where('myQuestion', isEqualTo: 'ageQuestion')
  .snapshots()
  .map(_someQuestionListFromSnapshot);
}

Is there a way to add an OR(||) operator or how can I do this so that I get results for both "nameQuestion" and "ageQuestion"? Kindly assist. Thanks.

Answer 1

Firestore does not support regular OR queries, but it does support IN queries with which you can implement what you need.

You query would look like citiesRef.where('country', 'in', ['USA', 'Japan']);

someCollection
  .where('myQUestion', whereIn: ['nameQuestion', 'ageQuestion'])

Also see:

• Firebase Firestore - OR query, which has answers that cover all kinds of variations of OR conditions.
• the Flutter reference documentation for the where method

Answer 2

You can do the following:

With getDocuments():

  void getData() async {
    List<Future<QuerySnapshot>> futures = [];

    var firstQuery = someCollection
        .where('myQUestion', isEqualTo: 'nameQuestion')
        .getDocuments();

    var secondQuery = someCollection
        .where('myQuestion', isEqualTo: 'ageQuestion')
        .getDocuments();

    futures.add(firstQuery);
    futures.add(secondQuery);

    List<QuerySnapshot> results = await Future.wait(futures);
    results.forEach((res) {
      res.documents.forEach((docResults) {
        print(docResults.data);
      });
    });
  }

So here you preform an OR query, and return the result from the two queries. Future.wait(futures) will wait until both of these queries are finished and return a `List that will contain the documents that satisfy these two queries.

---

With snapshots():

import 'package:async/async.dart' show StreamGroup;
///

        getData() async {
          List<Stream<QuerySnapshot>> streams = [];
          final someCollection = Firestore.instance.collection("users");
          var firstQuery = someCollection
              .where('myQUestion', isEqualTo: 'nameQuestion')
              .snapshots();

          var secondQuery = someCollection
              .where('myQuestion', isEqualTo: 'ageQuestion')
              .snapshots();

          streams.add(firstQuery);
          streams.add(secondQuery);

          Stream<QuerySnapshot> results = StreamGroup.merge(streams);
          await for (var res in results) {
            res.documents.forEach((docResults) {
              print(docResults.data);
            });
          }
        }

snapshots() returns a Stream which is a source of asynchronous data events, so it will keep listening for incoming data. To merge the two or query, you need to use StreamGroup.merge(streams) which merges the events from streams into a single single-subscription stream. Then using await for you can iterate over the events of a stream like the for loop iterates over an Iterable.

Check:

https://dart.dev/tutorials/language/streams

Answer 3

You cannot find a document using both where() calls because you are querying on the same myQUestion property. There is no way a property can hold two values at the same time. It can hold one or the other. You might be looking for an OR operator but using an AND in the way you do, it's not possible. An AND will only work when you query on different properties.