export class ProductService {
  productRef: AngularFireObject<any>;
  product: Observable<any>;

  constructor( private db: AngularFireDatabase ) {  }
  getOne( productId ) {
   this.productRef = this.db.object('/products' + productId);
   return this.product = this.productRef.snapshotChanges();
  }
}

export class ProductFormComponent implements OnInit {
  categories$;
  product: any;

  constructor(
    private router: Router,
    private route: ActivatedRoute,
    private categoriesService: CategoryService,
    private productService: ProductService
  ) { }

  ngOnInit() {
    this.categories$ = this.categoriesService.getCategories();
    const id = this.route.snapshot.paramMap.get('id');
    if ( id ) {
      this.productService.getOne( id ).take( 1 ).subscribe(
      p => this.product = p
    );
   }
  }
}

<form #f="ngForm" (ngSubmit)="save(f.value)" class="products">
  <div class="form-group"><label for="title">Title</label>
    <input #title="ngModel" [(ngModel)]="product.???.title" name="title"  type="text" class="form-control">
  </div>
  <button class="btn btn-primary">Save</button>
</form>

{ "payload": { "category": "africa", "imageUrl": "image 01", "price": 12, "title": "test04" }, "type": "value", "prevKey": null, "key": "-KzWO7MPXevJSgLEdKoT" }