Create, Read, Update and Delete angular Firestore | Angular 6

import { Injectable } from '@angular/core'; import { AngularFirestore, AngularFirestoreCollection, AngularFirestoreDocument } from 'angularfire2/firestore'; import { Observable } from 'rxjs/Observable'; import { Employee} from '../model/Employee'; @Injectable() export class EmployeeService { userscollection: AngularFirestoreCollection<Employee>; users: Observable<Employee[]>; userDoc: AngularFirestoreDocument<Employee>; constructor(public _afs: AngularFirestore) { } getData() { this.userscollection = this._afs.collection('employees', x => x.orderBy('firstName', 'asc')); this.users = this.userscollection.snapshotChanges().map( changes => { return changes.map( a => { const data = a.payload.doc.data() as Employee; data.id = a.payload.doc.id; return data; }); }); return this.users; } insertEmployee(employee : Employee) { this._afs.collection('employees').add({ firstName: employee.firstName , secondName: employee.secondName , gender: employee.gender , dateOfBirthday: employee.dateOfBirthday , category: employee.category , membership: employee.membership , address1: employee.address1 , state: employee.state , address2: employee.address2 , postcode: employee.postcode , city: employee.city , country: employee.country }); } deleteEmployee(id) { this.userDoc = this._afs.doc(`employees/${id}`); this.userDoc.delete(); } getDataById(id){ this.userDoc = this._afs.doc(`employees/${id}`);  return this.userDoc; } updateEmployee(employee : Employee){ this.userDoc.update( {      firstName: employee.firstName , secondName: employee.secondName , gender: employee.gender , dateOfBirthday: employee.dateOfBirthday , category: employee.category , membership: employee.membership , address1: employee.address1 , state: employee.state , address2: employee.address2 , postcode: employee.postcode , city: employee.city , country: employee.country } ); } } export class Employee { id:string; firstName: string; secondName: string; gender: string; dateOfBirthday: string; category: string; membership: string; address1: string; state: string; address2: string; postcode: string; city: string; country: string; power: string; alterEgo?: string }