Firestore : Retrieve a single document

Question

I want to retrieve a single document from Firestore. So I do not mean the list of documents in the collection (I know how to do that). Let's say I know one of the key-value pair of the document and I would like to find and retrieve the document into Angular 4.

interface Occupations {
	duration: number;
	id_entity: number;
	id_job: number;
	id_user: number;
	salary: number;
	start_time: number;
}

occupationDoc:AngularFirestoreDocument<Occupations>;
occupation: Observable<Occupations>;

<h1>A specific post:</h1>

  <h3>{{ (occupation | async)?.salary }}</h3>
  <p>{{ (occupation | async)?.id_user }}</p> 
  <p>{{ (occupation | async)?.duration }}</p> 
  <p>{{ (user | async)?.lastName }}</p> 

Answer 1

This is the solution I came up with :

//HTML
{{userInfo}}

//TypeScript
this.afs.collection('Occupations',
ref => ref.where('id_user', '==', this.idAuth)  
.limit(1))
.valueChanges()
.flatMap(result => result)
.subscribe(
    v => {
        let y = JSON.parse(JSON.stringify(v));
        this.userInfo = y.duration;                 
    }, 
    (error) => {
             console.log(error);
    }, () => {
        console.log('Finished');
    });