title: Angular firestore query to firestore document
body: <p>I have below query</p>
  
  <pre><code>    selectedUser$: AngularFirestoreDocument&lt;any&gt;;
      this.selectedUser$ = this.userCollection.ref.where('uid', '==', key)
  </code></pre>
  
  <p>Throwing error </p>
  
  <blockquote>
    <p>Type 'Query' is not assignable to type
    'AngularFirestoreDocument'.   Property 'ref' is missing in type
    'Query'.</p>
  </blockquote>
  
  <p>I tried</p>
  
  <pre><code>this.selectedUser$ = this.userCollection.ref.where('uid', '==', key).get()
  </code></pre>
  
  <p>no success</p>
  
  <p>Basically, I want the query to return firestore document</p>