Converting httpClient answer to model objects [Angular 6]

Question

I have a question about the Angular 5 httpClient.

This is a model class with a method foo() I'd like to receive from the server

export class MyClass implements Deserializable{
  id: number;
  title: string;

  deserialize(input: any) {
    Object.assign(this, input);
    return this;
  }

  foo(): string {
    // return "some string conversion" with this.title
  }
}

This is my service requesting it:

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';
import { MyClass } from './MyClass';

@Injectable({
  providedIn: 'root',
})
export class MyClassService {

  constructor(private http: HttpClient) {
  }

  getMyStuff(): Observable<MyClass[]> {
    // this is where I hope to convert the json to instances of MyClass
    return this.http.get<MyClass[]>('api/stuff')
  }
}

My Problem

When I ask the service for instances of MyClass I get the data, but I cannot run {{ item.foo() }} in the template. Also, when I console.log() the typeof of an item where it is received in the service, I do no see instances of an object of MyClass.

What am I doing wrong? I thought that writing this.http.get<MyClass[]>('api/stuff') would do the conversion.

Any hints? Thank you in advance!

Answer 1

When doing that, TypeScript only does "type assertion". It means that you're telling TypeScript that your object is of type MyClass, but the object isn't actually an instance of MyClass at runtime. In order to call functions defined in your model object, you have to define constructors in your model classes like that :

constructor(obj?: any) {
    Object.assign(this, obj);
}

Then in your services add a mapping like this :

http.get<MyClass>('/my-class').pipe(
      map(res => new MyClass(res))

Note: the code above is RxJS 6 style, i don't know which version you are using