Angular Firestore service

firestore-angular-service.ts

import { Injectable } from '@angular/core';
import { AngularFirestore, AngularFirestoreCollection, AngularFirestoreDocument } from 'angularfire2/firestore';
import { Observable } from 'rxjs/Observable';
import { Item } from '../models/Item';

@Injectable()
export class ItemService {

  itemsCollection: AngularFirestoreCollection<Item>;
  items: Observable<Item[]>;
  itemDoc: AngularFirestoreDocument<Item>;

  constructor(public afs: AngularFirestore) { 
  
    //this.items = this.afs.collection('items').valueChanges();

    this.itemsCollection = this.afs.collection('items', ref => ref.orderBy('title','asc'));

    // For some versions 
    // this.items = this.itemsCollection.snapshotChanges().map(changes => {
    //  return changes.map(a => {
    //    const data = a.payload.doc.data() as Item;
    //    data.id = a.payload.doc.id;
    //    return data;
    //  });
    // }); 
    
    this.items = this.itemsCollection.snapshotChanges().pipe(map(s =>
      s.map(m => m.payload.doc.data() as Item)
    ));
  }

  getItems(){
    return this.items;
  }

  addItem(item: Item){
    this.itemsCollection.add(item);
  }

  deleteItem(item: Item){
    this.itemDoc = this.afs.doc(`items/${item.id}`);
    this.itemDoc.delete();
  }

  updateItem(item: Item){
    this.itemDoc = this.afs.doc(`items/${item.id}`);
    this.itemDoc.update(item);
  }
}