How can I make the ID of this document in firestore `QEoevSjHlswgk44nVTsr` dynamic, that is, change according to the IDs in that collection? I'm using angularfire2: ^5.0.0-rc.11

This is what I have:

**firebase.service.ts**

```
proyectos: Observable<Proyecto[]>;

getImagenDestacada() {
    this.proyectos = this.afs.collection('proyectos').doc('QEoevSjHlswgk44nVTsr').collection('archivos', ref => ref
    .orderBy('nombre','asc').limit(1)
    ).snapshotChanges().pipe(map(actions => {
      return actions.map(a => {
        const data = a.payload.doc.data() as Proyecto;
        const id = a.payload.doc.id; 
        return { id, ...data };
      });
    }));
    return this.proyectos
    }

```

========================

I have tried the following:

**firebase.service.ts**

```
getImagenDestacada(id:string) {
this.proyectos = this.afs.collection('proyectos').doc(id).collection('archivos', ref => ref
.orderBy('nombre','asc').limit(1)
).snapshotChanges().pipe(map(actions => {
  return actions.map(a => {
    const data = a.payload.doc.data() as Proyecto;
    const id = a.payload.doc.id; 
    return { id, ...data };
  });
}));
return this.proyectos
}

```

**portafolio.component.ts**

```
archivos: Observable<Proyecto[]>;

this.archivos = this.fs.getImagenDestacada(this.id);

```

But I get the following error:

> 
> Error: Function CollectionReference.doc() requires its first argument to be of type string, but it was: undefined
> 
> 
>