Angular 2 correct way to get data from server - forms

Question

I want to get data from the database. I'm following the examples at angular.io webpage but I don't know if I'm doing right.
I have a form and when a user fills the postal code field, I call the database to get the name of the city or, if it doesn't exist, ask the user to fill it.
My problem is I don't know how to correctly do it.
In my service.
checkCp(city: City): Observable<any> {
return this.http.get<any>(this.backendUrl + 'api/city/' + city.cp).pipe(
tap(city => console.log("fetched"))
);
}
and this is in my component.js
checkCp(): void {
this.modal.header = 'Searching city';
this.modal.text = 'Please wait';
this.openWaitModal();
this.studentService.checkCp(this.city)
.subscribe(cityFromDb => {
if(cityFromDb ===null) {
this.closeWaitModal();
this.modal.header = 'Postal code not found';
this.modal.text = 'Insert the name of the city';
this.modal.no = 'Cancel';
this.modal.yes = 'Insert';
this.modal.action = 'newCity';
this.modal.enableInput = true;
this.openModal();
}else{
this.closeWaitModal();
this.city = cityFromDb.city; // I can't access cityFromDb.name
// i access via cityFromDb.city.name
}
}, err => {
this.errorHandler(err);
})
}

Answer 1

You would call your service as follows:
checkCp(city: City): Observable<any> {
return this.http.get<any>(this.backendUrl + 'api/city/' + city.cp);
};
This will return an Observable to your component.ts
The code in your component.ts should work now