add method
Adds a new document to this collection with the specified data
,
assigning it a document ID automatically.
The data
parameter must not be null.
Returns non-null Future that resolves with a DocumentReference pointing to the newly created document after it has been written to the backend.
Implementation
Future<DocumentReference> add(Map<String, dynamic> data) =>
handleThenable(jsObject.add(jsify(data)))
.then(DocumentReference.getInstance);