Firebase Location Query

问题:

I am designing a location based restaurant search application on android with firebase. Restaurant class as follows on firebase;

 restaurants
-key
  address: "NYC"
  city: "New York"
  description: ""
  id: 60000
  latitude: 39.895107
  longitude: 32.797819
  name: "Pizza Store"

Fragment class

mainActivity.mDatabase.child("restaurants").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot snapshot) {
            System.out.println("There are " + snapshot.getChildrenCount() + " restaurans");
            for (DataSnapshot postSnapshot : snapshot.getChildren()) {
                Restaurant post = postSnapshot.getValue(Restaurant.class);
                mapmap2.put(post.getName(), postSnapshot.getKey());
                restaurants.add(post);
            }
            adapter = new RestaurantCardViewAdapter(getActivity(), restaurants, MapListFragment.this);
            mRecyclerView.setAdapter(adapter);
        }

        @Override
        public void onCancelled(DatabaseError firebaseError) {
            System.out.println("The read failed: " + firebaseError.getMessage());
        }
    });

Right now, I can list all the restaurants. But I want to query on user location. Firstly I want to list 20 restaurants near to user location and when user loads page through I want to get next 20 nearest restaurants. I do some search on internet. I found GeoFire library but as I understand its working with the legacy version of firebase. How can I query with these criterias?

回答1:

Firebase Queries can only filter/order by a single property. Since a location consists of longitude and latitude, in the format you have right now, you cannot query based on location.

Luckily there is an add-on library called GeoFire. This library combines the longitude and latitude into a single property called a geohash. Based on this property it can filter by distance to a given location.

I recommend you check out Geofire and see if it fits your use-case.

回答2:

I solved the problem with the help of answers. I push a seperate child for geofire named as "restaurant_locations". I push the locations seperately when I insert restaurants.

      GeoFire geoFire;
      String itemId = mDatabase.child("restaurants").push().getKey();
      mDatabase.child("restaurants").child(itemId).setValue(restaurant);

      geoFire = new GeoFire(mDatabase.child("restaurants_location"));
      geoFire.setLocation(itemId, new GeoLocation(Double.valueOf(rd.location.latitude), Double.valueOf(rd.location.longitude)));

Then when I need to query through locations I used geofire query.

    geoFire = new GeoFire(mDatabase.child("restaurants_location"));
    GeoQuery geoQuery = geoFire.queryAtLocation(new GeoLocation(39.896263, 32.799652), 1);

    geoQuery.addGeoQueryEventListener(new GeoQueryEventListener() {
        @Override
        public void onKeyEntered(String key, GeoLocation location) {
            System.out.println(String.format("Key %s entered the search area at [%f,%f]", key, location.latitude, location.longitude));
            mDatabase.child("restaurants").child(key).addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot snapshot) {
                    Restaurant res= snapshot.getValue(Restaurant.class);
                }
                @Override
                public void onCancelled(DatabaseError firebaseError) {
                    System.out.println("The read failed: " + firebaseError.getMessage());
                }

                // ...
            });
        }

        @Override
        public void onKeyExited(String key) {
            System.out.println(String.format("Key %s is no longer in the search area", key));
        }

        @Override
        public void onKeyMoved(String key, GeoLocation location) {
            System.out.println(String.format("Key %s moved within the search area to [%f,%f]", key, location.latitude, location.longitude));
        }

        @Override
        public void onGeoQueryReady() {
            System.out.println("All initial data has been loaded and events have been fired!");
        }

        @Override
        public void onGeoQueryError(DatabaseError error) {
            System.err.println("There was an error with this query: " + error);
        }
    });

But I still worry about that is it the most efficient way of getting Restaurants from database, because I run query seperately for every single restaurant key on "restaurants" root. Is there anybody know more efficient way please let us know.