[FIXED] Firestore geoquery on nested firestore collection

Issue

Following the tutorial https://firebase.google.com/docs/firestore/solutions/geoqueries and https://www.youtube.com/watch?v=mx1mMdHBi5Q i've created my database design which looks like

When I'm querying for any location I'm always getting 0 result, then I tried querying non nested collection (as shown in tutorial video https://www.youtube.com/watch?v=mx1mMdHBi5Q) then I'm getting the result.

My non nested collection design looks like:

Code for nested collection (which is my requirement and doesn't work)

public void queryHashes() {
    // Find cities within 50km of London
    final GeoLocation center = new GeoLocation(19.912524, 76.079626);
    final double radiusInM = 50 * 1000;

    // Each item in 'bounds' represents a startAt/endAt pair. We have to issue
    // a separate query for each pair. There can be up to 9 pairs of bounds
    // depending on overlap, but in most cases there are 4.
    List<GeoQueryBounds> bounds = GeoFireUtils.getGeoHashQueryBounds(center, radiusInM);
    final List<Task<QuerySnapshot>> tasks = new ArrayList<>();
    for (GeoQueryBounds b : bounds) {
        Query q = db.collection("Owners").document().collection("Ghars")
                .orderBy("geohash")
                .startAt(b.startHash)
                .endAt(b.endHash);

        tasks.add(q.get());
    }

    // Collect all the query results together into a single list
    Tasks.whenAllComplete(tasks)
            .addOnCompleteListener(new OnCompleteListener<List<Task<?>>>() {
                @Override
                public void onComplete(@NonNull Task<List<Task<?>>> t) {
                    List<DocumentSnapshot> matchingDocs = new ArrayList<>();

                    for (Task<QuerySnapshot> task : tasks) {
                        QuerySnapshot snap = task.getResult();
                        for (DocumentSnapshot doc : snap.getDocuments()) {
                            double lat = doc.getDouble("lat");
                            double lng = doc.getDouble("lng");

                            // We have to filter out a few false positives due to GeoHash
                            // accuracy, but most will match
                            GeoLocation docLocation = new GeoLocation(lat, lng);
                            double distanceInM = GeoFireUtils.getDistanceBetween(docLocation, center);
                            if (distanceInM <= radiusInM) {
                                matchingDocs.add(doc);
                            }
                        }
                    }

                    // matchingDocs contains the results
                    // ...
                    Log.v("matchingDocsD", matchingDocs.size()+"");
                }
            });
}

Code for non-nested collection (which works)

public void queryHashes() {
    // Find cities within 50km of London
    final GeoLocation center = new GeoLocation(19.912524, 76.079626);
    final double radiusInM = 50 * 1000;

    // Each item in 'bounds' represents a startAt/endAt pair. We have to issue
    // a separate query for each pair. There can be up to 9 pairs of bounds
    // depending on overlap, but in most cases there are 4.
    List<GeoQueryBounds> bounds = GeoFireUtils.getGeoHashQueryBounds(center, radiusInM);
    final List<Task<QuerySnapshot>> tasks = new ArrayList<>();
    for (GeoQueryBounds b : bounds) {
        Query q = db.collection("10K")
                .orderBy("geohash")
                .startAt(b.startHash)
                .endAt(b.endHash);

        tasks.add(q.get());
    }

    // Collect all the query results together into a single list
    Tasks.whenAllComplete(tasks)
            .addOnCompleteListener(new OnCompleteListener<List<Task<?>>>() {
                @Override
                public void onComplete(@NonNull Task<List<Task<?>>> t) {
                    List<DocumentSnapshot> matchingDocs = new ArrayList<>();

                    for (Task<QuerySnapshot> task : tasks) {
                        QuerySnapshot snap = task.getResult();
                        for (DocumentSnapshot doc : snap.getDocuments()) {
                            double lat = doc.getDouble("lat");
                            double lng = doc.getDouble("lng");

                            // We have to filter out a few false positives due to GeoHash
                            // accuracy, but most will match
                            GeoLocation docLocation = new GeoLocation(lat, lng);
                            double distanceInM = GeoFireUtils.getDistanceBetween(docLocation, center);
                            if (distanceInM <= radiusInM) {
                                matchingDocs.add(doc);
                            }
                        }
                    }

                    // matchingDocs contains the results
                    // ...
                    Log.v("matchingDocsD", matchingDocs.size()+"");
                }
            });
}

Solution

This query will never return any results:

Query q = db.collection("Owners").document().collection("Ghars")
        .orderBy("geohash")
        .startAt(b.startHash)
        .endAt(b.endHash);

When you call document() without any arguments, you're creating a reference to a new, non-existing document. So its Ghars subcollection won't exist either, and your query gets no results.

---

If you want to query a specific owner's Ghars subcollection, you should specify the owner's document ID in the call to document():

                                        // 👇
Query q = db.collection("Owners").document(ownerDocId).collection("Ghars")
        .orderBy("geohash")
        .startAt(b.startHash)
        .endAt(b.endHash);

---

If you want to query across all Ghars subcollections, you can use a collection group query, which queries all collections with a specific name:

                   // 👇
Query q = db.collectionGroup("Ghars")
        .orderBy("geohash")
        .startAt(b.startHash)
        .endAt(b.endHash);

Answered By - Frank van Puffelen
Answer Checked By - Marie Seifert (JavaFixing Admin)