title: Firestore adding hashmaps to a map field in Firestore
body: <p>I am trying to create a map of objects in my firestore database using key->value pairs. 
  The idea is to have a map of room objects within my Properties documents where living room would be the key and the object that value. Like the image below</p>
  
  <p><a href="https://i.stack.imgur.com/EhUYx.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EhUYx.jpg" alt="rooms map"></a></p>
  
  <p><a href="https://i.stack.imgur.com/7rswi.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7rswi.jpg" alt="rooms map"></a></p>
  
  <p>I am getting lost with the correct way to add the objects into firestore as the rooms map is already there so how do I add a key->value pair into it ?? 
  I also need to perform the search I have in the below code so I can grab the Properties document and add the objects into the room map field</p>
  
  <pre><code>FirebaseFirestore db = FirebaseFirestore.getInstance();
  final CollectionReference propertyRef = db.collection("Properties");
  
  final Room room = new Room(roomName, feet, inches, imageUrl);
  
  propertyRef.whereEqualTo("propertyId", propertyId).get().addOnCompleteListener(new OnCompleteListener&lt;QuerySnapshot&gt;() {
  
  @Override
  public void onComplete(@NonNull Task&lt;QuerySnapshot&gt; task) {
       if (task.isSuccessful()) {
            for (QueryDocumentSnapshot doc : Objects.requireNonNull(task.getResult())) {
                propertyRef.document(doc.getId())
       -----&gt;   .update("rooms", ""+roomName+"", room);
  
                Log.d(TAG, "Firebase Success= " + imageUrl);
                Toast.makeText(CreatePropertyActivity3.this, "Property Created", Toast.LENGTH_LONG).show();
                exProperties();
                }
                } else {
                    Toast.makeText(CreatePropertyActivity3.this, "Error check log", Toast.LENGTH_LONG).show();
       }
     }
   });
  </code></pre>