Confirmed populated array of objects returns empty

Question

I have a method that is failing when returning an array of objects. As mentioned in the title - the array is confirmed to be populated but is empty in the response.

Here is the full flow:

The Url:

http://localhost:53000/api/v1/landmarks?lat=40.76959&lng=-73.95136&radius=160

Is routed to the corresponding index:

api.route('/api/v1/landmarks').get(Landmark.list);

The Index Calls a Service:

exports.list = (req, res) => {

    const landmark = new LandmarkService();

    landmark.getLandmarks(req)
        .then(landmarks => {

            var response = new Object();
                response.startindex = req.query.page;
                response.limit = req.query.per_page;
                response.landmarks = landmarks;

                res.json(response);
        })
        .catch(err => {
            logger.error(err);
            res.status(422).send(err.errors);
        });
};

The Service Method Uses a Data Access Class to Return the Promise

  getLandmarks(req) {

    const params = req.params || {};
    const query = req.query || {};
    const page = parseInt(query.page, 10) || 1;
    const perPage = parseInt(query.per_page, 10);
    const userLatitude = parseFloat(query.lat); 
    const userLongitude = parseFloat(query.lng); 
    const userRadius = parseFloat(query.radius) || 10;
    const utils = new Utils();
    const data = new DataService();
    const landmarkProperties = ['key','building','street','category','closing', 
            'email','name','opening','phone','postal','timestamp','type','web'];

    return data.db_GetAllByLocation(landmarksRef, landmarkLocationsRef, 
                    landmarkProperties, userLatitude, userLongitude, userRadius);

    } // getLandmarks

However, the response is always empty.

I am building an array in the called method and populating it with JSON objects. That is what is supposed to be sent back in the response. I can confirm that the attributes array is correctly populated before I hit the return statement. I can log it to the console. I can also send back a test array filled with stub values successfully.

I have a feeling it is how I am setting things up inside the Promise?

Data Access Method That Should Return Array of Objects:

db_GetAllByLocation(ref, ref_locations, properties, user_latitude, user_longitude, user_radius)
{  
        const landmarkGeoFire = new GeoFire(ref_locations);
        var geoQuery = landmarkGeoFire.query({
                center: [user_latitude, user_longitude], 
                radius: user_radius
        });
        var locations = [];
        var onKeyEnteredRegistration = geoQuery.on("key_entered", function (key, coordinates, distance) {
            var location = {}; 
                location.key = key;
                location.latitude = coordinates[0];
                location.longitude = coordinates[1];
                location.distance = distance;
                locations.push(location);                   
        });
        var attributes = [];
        var onReadyRegistration = geoQuery.on("ready", function() {
            ref.on('value', function (refsSnap) {
                   refsSnap.forEach((refSnap) => {
                        var list = refSnap;
                        locations.forEach(function(locationSnap) 
                        {
                            //console.log(refSnap.key, '==', locationSnap.key);
                            if (refSnap.key == locationSnap.key) 
                            {
                                var attribute = {};
                                for(var i=0; i<=properties.length-1; i++)
                                {
                                    if(properties[i] == 'key') {
                                        attribute[properties[i]] = refSnap.key;
                                        continue;
                                    }
                                    attribute[properties[i]] = list.child(properties[i]).val();
                                }
                                attribute['latitude'] = locationSnap.latitude;
                                attribute['longitude'] = locationSnap.longitude;
                                attribute['distance'] =  locationSnap.distance;
                                attributes.push(attribute);    
                            } // refSnap.key == locationSnap.key
                        }); // locations.forEach
                    }); // refsSnap.forEach
                    return Promise.resolve(attributes); <-- does not resolve (throws 'cannot read property .then')
                  //geoQuery.cancel();
                }); // ref.on
        }); // onreadyregistration      

        return Promise.resolve(attributes); <-- comes back empty
}

Answer 1

It seems that data.db_GetAllByLocation is an asynchronous function, therefore the call resolve(landmarks); is getting called before the execution of the async function is finished. If the data.db_GetAllByLocation returns a promise then call the resolve(landmarks) inside the promise.

data.db_GetAllByLocation().then(function() {
  resolve();
})

Also try the following modified db_GetAllByLocation()

db_GetAllByLocation(ref, ref_locations, properties, user_latitude, user_longitude, user_radius)
    {       
   return new Promise(function(resolve, reject){
    const landmarkGeoFire = new GeoFire(ref_locations);

    var geoQuery = landmarkGeoFire.query({
      center: [user_latitude, user_longitude], 
      radius: user_radius
    });

    var locations = [{}];

    var onKeyEnteredRegistration = geoQuery.on("key_entered", function (key, coordinates, distance) {
     var location = {}; 
      location.key = key;
      location.latitude = coordinates[0];
      location.longitude = coordinates[1];
      location.distance = distance;
      locations.push(location);                   

    });

      var attributes = [{}];

    var onReadyRegistration = geoQuery.on("ready", function() {
     ref.on('value', function (refsSnap) {
         refsSnap.forEach((refSnap) => {
        var list = refSnap;
        locations.forEach(function(locationSnap) 
        {
         if (refSnap.key == locationSnap.key) 
         {
          var attribute = {};
          for(var i=0; i<=properties.length-1; i++)
          {
           if(properties[i] == 'key') {
            attribute[properties[i]] = refSnap.key;
            continue;
           }
           attribute[properties[i]] = list.child(properties[i]).val();
          }

          attribute['latitude'] = locationSnap.latitude;
          attribute['longitude'] = locationSnap.longitude;
          attribute['distance'] =  locationSnap.distance;
          attributes.push(attribute);    
         } // refSnap.key == locationSnap.key
        }); // locations.forEach
       }); // refsSnap.forEach
       // return JSON.stringify(attributes);
       return resolve(attributes);
      }); // ref.on
    

    }); // onreadyregistration

   });
            
} 

Answer 2

OK, I sorted this by removing all my code and writing some test logic (I should have done this before I posted my question).

The below flow works for me, and, applied back to my code, gave me the results I was looking for. No need to re-post the code, but maybe the below flow will be helpful to somebody.

route

api.route('/api/v1/landmarks').get(Landmark.test);

index

exports.test = (req, res) => {

    const landmark = new LandmarkService();

    landmark.getLandmarksTest(req)
        .then(landmarks => {
            var final = {};
                final.attr1 = 'attr1';
                final.attr2 = 'attr2';
                final.landmarks = landmarks;
                res.json(final);
        })
        .catch(err => {
            logger.error(err);
            res.status(422).send(err.errors);
        });

};

service method

getLandmarksTest(req)
{

            const data = new DataService();

        data.db_PromiseTest().then(results => {
                return Promise.resolve(results);
          }).catch(err => {
                return Promise.reject(err.errors);
          });




}

data layer method

db_PromiseTest()
{
            var stub = {
                    "name": "Madame Uppercut",
                    "age": 39,
                    "secretIdentity": "Jane Wilson",
                    "powers": [
                    "Million tonne punch",
                    "Damage resistance",
                    "Superhuman reflexes"
                    ]
                };

                 return Promise.resolve(stub);


}