update method
this will update certain values presented in the doc object
Implementation
Future<WriteResult> update(
Map<String, dynamic> doc, {
bool upsert = true,
}) async {
var selector = where.eq('_id', _id);
var updateQuery = modify;
doc.forEach((key, value) {
updateQuery = updateQuery.set(key, value);
});
return _collRef.updateOne(selector, updateQuery, upsert: upsert);
}