How to add subcollection to a document in Firebase Cloud Firestore

Question

The documentation does not have any examples on how to add a subcollection to a document. I know how to add document to a collection and how to add data to a document, but h

Answer 1

too late for an answer but here is what worked for me,

        mFirebaseDatabaseReference?.collection("conversations")?.add(Conversation("User1"))
            ?.addOnSuccessListener { documentReference ->
                Log.d(TAG, "DocumentSnapshot written with ID: " + documentReference.id)
                mFirebaseDatabaseReference?.collection("conversations")?.document(documentReference.id)?.collection("messages")?.add(Message(edtMessage?.text.toString()))
            }?.addOnFailureListener { e ->
                Log.w(TAG, "Error adding document", e)
            }

add success listener for adding document and use firebase generated ID for a path. Use this ID for the complete path for a new collection you want to add. I.E. - dbReference.collection('yourCollectionName').document(firebaseGeneratedID).collection('yourCollectionName').add(yourDocumentPOJO/Object)