fix(database): call apply instead of call

RxJS merge takes a variable number of observables - not an array - so
apply should be called instead of call. Fixed the related test, too.

Author: cartant

src/database/query_observable.spec.ts

@@ -92,7 +92,6 @@ describe('observeQuery', () => {
 
 
   it('should omit only the orderBy type of the last emitted orderBy observable', () => {
-    // TODO: Should we allow re-emitting of the orderBy method?
     var nextSpy = jasmine.createSpy('next');
     var query = {
       orderByKey: new Subject<boolean>(),
@@ -108,13 +107,19 @@ describe('observeQuery', () => {
     });
     nextSpy.calls.reset();
     query.orderByKey.next(true);
-    expect(nextSpy).not.toHaveBeenCalled();
-    // nextSpy.calls.reset();
-    // query.orderByValue.next(true);
-    // expect(nextSpy).toHaveBeenCalledWith({orderByValue: true});
-    // nextSpy.calls.reset();
+    expect(nextSpy).toHaveBeenCalledWith({
+      orderByKey: true
+    });
+    nextSpy.calls.reset();
+    query.orderByValue.next(true);
+    expect(nextSpy).toHaveBeenCalledWith({
+      orderByValue: true
+    });
+    nextSpy.calls.reset();
     query.orderByChild.next('foo');
-    expect(nextSpy).toHaveBeenCalledWith({orderByChild: 'foo'});
+    expect(nextSpy).toHaveBeenCalledWith({
+      orderByChild: 'foo'
+    });
   });
 });
 

src/database/query_observable.ts

@@ -23,8 +23,8 @@ export function observeQuery(query: Query): Observable<ScalarQuery> {
 
   return Observable.create((observer: Observer<ScalarQuery>) => {
 
-    let obs = getOrderObservables(query) as Observable<OrderBySelection>;
-    combineLatest.call(obs,
+    combineLatest.call(
+        getOrderObservables(query),
         getStartAtObservable(query),
         getEndAtObservable(query),
         getEqualToObservable(query),
@@ -80,7 +80,7 @@ export function observeQuery(query: Query): Observable<ScalarQuery> {
   });
 }
 
-export function getOrderObservables(query: Query): Observable<OrderBySelection> | Observable<OrderBySelection | Observable<OrderBySelection>> {
+export function getOrderObservables(query: Query): Observable<OrderBySelection> {
   var observables = ['orderByChild', 'orderByKey', 'orderByValue', 'orderByPriority']
     .map((key: string, option: OrderByOptions) => {
       return ({ key, option })
@@ -93,15 +93,15 @@ export function getOrderObservables(query: Query): Observable<OrderBySelection>
   if (observables.length === 1) {
     return observables[0];
   } else if (observables.length > 1) {
-    return merge.call(observables[0], observables.slice(1));
+    return merge.apply(observables[0], observables.slice(1));
   } else {
     return new Observable<OrderBySelection>(subscriber => {
       subscriber.next(null);
     });
   }
 }
 
-export function getLimitToObservables(query: Query): Observable<LimitToSelection> | Observable<LimitToSelection | Observable<LimitToSelection>> {
+export function getLimitToObservables(query: Query): Observable<LimitToSelection> {
   var observables = ['limitToFirst', 'limitToLast']
     .map((key: string, option: LimitToOptions) => ({ key, option }))
     .filter(({key, option}: { key: string, option: LimitToOptions }) => !isNil(query[key]))
@@ -110,7 +110,7 @@ export function getLimitToObservables(query: Query): Observable<LimitToSelection
   if (observables.length === 1) {
     return observables[0];
   } else if (observables.length > 1) {
-    const mergedObs = merge.call(observables[0], observables.slice(1));
+    const mergedObs = merge.apply(observables[0], observables.slice(1));
     return mergedObs;
   } else {
     return new Observable<LimitToSelection>(subscriber => {