refactor(db): create push id method

Author: davideast

src/database/database.ts

@@ -29,6 +29,10 @@ export class AngularFireDatabase {
     return createObjectReference<T>(ref);    
   }
 
+  createPushId() {
+    return this.database.ref().push().key;
+  }
+
 }
 
 export { 

src/database/list/changes.ts

@@ -1,12 +1,12 @@
 import { fromRef } from '../observable/fromRef';
 import { Observable } from 'rxjs/Observable';
-import { DatabaseQuery, ChildEvent, SnapshotChange, AngularFireAction} from '../interfaces';
+import { DatabaseQuery, ChildEvent, SnapshotChange, AngularFireAction, SnapshotAction } from '../interfaces';
 import { positionFor, positionAfter } from './utils';
 import 'rxjs/add/operator/scan';
 import 'rxjs/add/observable/merge';
 
 // TODO(davideast): check safety of ! operator in scan
-export function listChanges<T>(ref: DatabaseQuery, events: ChildEvent[]): Observable<AngularFireAction<any>[]> {
+export function listChanges<T>(ref: DatabaseQuery, events: ChildEvent[]): Observable<SnapshotAction[]> {
   const childEvent$ = events.map(event => fromRef(ref, event));
   return Observable.merge(...childEvent$)
   .scan((current, action) => {

src/database/list/state-changes.ts

@@ -6,23 +6,6 @@ import { database } from 'firebase/app';
 import 'rxjs/add/observable/merge';
 import 'rxjs/add/operator/scan';
 
-/**
- * NOTES FOR LATER:
- * Consider have snapshotChanges() return a SnapshotAction because it 
- * retains the event information.
- * 
- * Consider having valueChanges(), snapshotChanges(), and stateChanges()
- * return an Action. For snapshotChanges it would be an
- * Action<SnapshotPrevKey> and for valueChanges it would be an Action<T>.
- * 
- * Consider providing the delta changes for both valueChanges() and 
- * snapshotChanges().
- * 
- * Consider providing an auditTrail() method that scans over stateChanges()
- * to provide each action as an array at that occurred at that location. This
- * would be a loaded dataset.
- */
-
 export function createStateChanges(query: DatabaseQuery) {
   return (events?: ChildEvent[]) => stateChanges(query, events);
 }