how to add new data to existing map in firebase flutter

Question

here is the firebase document data

I want to add a new map value to the purchased-id. this is the current code

FirebaseFirestore.instance.collection('users').doc(userID).set({
  'purchased-id': {
    widget.head: widget.id,
  }
});

but with this code the map value is replaced, how do I add another map value to the existing map

like this

user_11566161 · Answer

I think need merge: true to update the map with its new value.

FirebaseFirestore.instance.collection('users').doc(userID).set({
  'purchased-id': {
    widget.head: widget.id,
  }
}, SetOptions(merge: true));

Also to differentiate with .set and .update, have a look at this answer: https://stackoverflow.com/a/47554197/11566161