insert method
Implementation
Future insert(Map<String, dynamic> record) async {
if (record.containsKey(ID_KEY) && record[ID_KEY] != null) throw Exception("'entityId' must be 'null' to insert the record in collection");
var entityId = await _collection.generateKey(_database);
record[ID_KEY] = entityId;
await _collection.record(entityId).add(_database, record);
}