I am using `AuthService` to call my MySql database with PHP api and therefore my PHP functions for my Ionic 3 Angular 4 app.

This is how I call to get `userData` and it works fine

```
import { AuthService } from "../../providers/auth-service";

...

constructor(
  public authService: AuthService,
  private loadingCtrl: LoadingController
) {
  const data = JSON.parse(localStorage.getItem("userData"));
  this.userDetails = data.userData;
  this.userPostData.uid = this.userDetails.uid;
  let loader = this.loadingCtrl.create({
    content: 'Please wait...'
  });
}

```

I have another project that uses `AngularFirestore`

```
import { AngularFirestore, AngularFirestoreDocument } from  'angularfire2/firestore';
import { AngularFireAuth } from 'angularfire2/auth';
import { Storage } from '@ionic/storage';

```

and calls the `constructor` like this

```
private users: AngularFirestoreDocument<{}>;

constructor(
  public navCtrl: NavController,
  private afService: AngularFirestore,
  private storage: Storage,
  private loadingCtrl: LoadingController,
  private afAuth: AngularFireAuth
) {
  this.uid = localStorage.getItem('uid');
  this.users = this.afService.collection('users').doc(this.uid);
  let loader = this.loadingCtrl.create({
    content: 'Please wait...'
  });
  loader.present();
  this.users.valueChanges()
    .subscribe((res: any) => {
      this.canDoMessage = res.canDoMessage;
      loader.dismiss();
    }, error => {
      loader.dismiss();
    });
}

```

I just want to understand what calling `this.afService.collection` does?

Basically what i am asking is how to call the 'users' on AuthService

```
  constructor( public authService: AuthService,,

```

like this on Firestone

```
  constructor(private afService: AngularFirestore) { **this.users = afService.collection('users')**; }

```