Flutter Multiple Firestore Queries

Question

I am trying to make multiple queries to Firestore and merge the results into one stream like here . I tried using StreamGroup.merge() but it's only returning the results of one stream. I noticed that it does actually get data for all the streams but only returns one when everything completes. Here is what I did:

Stream getStream(){
    List<Stream> streams = [];     

    streams.add(Firestore.instance.collection(Constants.REQUESTS_NODE).
    where("municipality",isEqualTo: "City of Johannesburg Metropolitan").
    where("service_id",isEqualTo: 2).
    snapshots());
    streams.add(Firestore.instance.collection(Constants.REQUESTS_NODE).
    where("municipality",isEqualTo: "Lesedi Local").where("service_id",isEqualTo: 2).
    snapshots());    

    return StreamGroup.merge(streams);

  }

What am I missing and doing wrong? The reason I'm doing this is to compensate for Firestore's lack of OR operator.

Answer 1

I found this online, hope it helps:

`import 'package:async/async.dart';

Stream<DocumentSnapshot> stream1 = firestore.document('/path1').snapshots();
Stream<DocumentSnapshot> stream2 = firestore.document('/path2').snapshots();
StreamZip bothStreams = StreamZip([stream1, stream2]);

// To use stream
bothStreams.listen((snaps) {
 DocumentSnapshot snapshot1 = snaps[0];
 DocumentSnapshot snapshot2 = snaps[1];

 // ...
});`

Answer 2

You can use whereIn condition, it's a List<dynamic> , that's work with me!

For example:

Firestore db = Firestore.instance;
db.collection
.where("status", whereIn: ["available", "unavailable", "busy"])
.getDocuments();

Answer 3

For anyone in future who might need assistance with this, I managed to solve it using StreamZip . You can read more about it from this website

Answer 4

Use collectionGroup()

A collection group consists of all collections with the same ID. By default, queries retrieve results from a single collection in your database. Use a collection group query to retrieve documents from a collection group instead of from a single collection.

Example from docs

For example, you can create a landmarks collection group by adding a landmarks subcollection to each city:

final citiesRef = FirebaseFirestore.instance.collection("cities");

final ggbData = {"name": "Golden Gate Bridge", "type": "bridge"};
citiesRef.doc("SF").collection("landmarks").add(ggbData);

final lohData = {"name": "Legion of Honor", "type": "museum"};
citiesRef.doc("SF").collection("landmarks").add(lohData);

final gpData = {"name": "Griffth Park", "type": "park"};
citiesRef.doc("LA").collection("landmarks").add(gpData);

final tgData = {"name": "The Getty", "type": "museum"};
citiesRef.doc("LA").collection("landmarks").add(tgData);

final lmData = {"name": "Lincoln Memorial", "type": "memorial"};
citiesRef.doc("DC").collection("landmarks").add(lmData);

final nasaData = {
  "name": "National Air and Space Museum",
  "type": "museum"
};
citiesRef.doc("DC").collection("landmarks").add(nasaData);

final upData = {"name": "Ueno Park", "type": "park"};
citiesRef.doc("TOK").collection("landmarks").add(upData);

final nmData = {
  "name": "National Musuem of Nature and Science",
  "type": "museum"
};
citiesRef.doc("TOK").collection("landmarks").add(nmData);

final jpData = {"name": "Jingshan Park", "type": "park"};
citiesRef.doc("BJ").collection("landmarks").add(jpData);

final baoData = {"name": "Beijing Ancient Observatory", "type": "musuem"};
citiesRef.doc("BJ").collection("landmarks").add(baoData);

We can use the simple and compound query described earlier to query a single city's landmarks subcollection, but you might also want to retrieve results from every city's landmarks subcollection at once.

The landmarks collection group consists of all collections with the ID landmarks, and you can query it using a collection group query. For example, this collection group query retrieves all museum landmarks across all cities:

FirebaseFirestore.instance
    .collectionGroup("landmarks")
    .where("type", isEqualTo: "museum")
    .get()
    .then(
      (res) => print("Successfully completed"),
      onError: (e) => print("Error completing: $e"),
    );