title: how to get list of document in a collection, using angular firestore
body: <p>I a m trying to get the list of documents in collections, but m not getting any document,
  This is code what i m trying-
  `</p>
  <pre class="lang-js prettyprint-override"><code>    schoolProductCollectionFetch(schoolName){
      
         const school = this.db.collection(schoolName)
         this.school$ = school.snapshotChanges().pipe(map(schoollist=&gt;schoollist.map(s=&gt;{
           const data = s.payload.doc.id;
           console.log(data);
           return data;
         })));
         return this.school$
       
        }
  </code></pre>
  <p>Database Format:
  SchoolCollection-&gt;Documents-&gt;ProductCollection</p>
  <pre><code>SchoolCollection:{
     1st:{products:{}},
     2nd:{products:{}},
  }
  </code></pre>
  <p>Have tried to represent the data format as in firestore, I want to get 1st, 2nd which are document id's for SchoolCollection,
  Schema Snap:</p>
  <p><a href="https://i.stack.imgur.com/tek8u.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tek8u.png" alt="Schema Screenshot" /></a>
  Note: Please let me know if more details needed to understand the query</p>