When working with orders the main identifier is OrderTransactionId, not OrderId. This is done because the OrderId generated by the exchange. Because of this, immediately after the execution the ConnectorRegisterOrder(Order) method, for some time the OrderId can not be initialized. Therefore, at once after the transaction sending, the trading program generates OrderTransactionId.
OrderTransactionId automatically generated by the class. This is an abstract class that has two standard implementations: