public static bool SetInstance(string login, string password, ISellerUnitOfWork unitOfWork)
 {
     if (_instance == null)
     {
         var employee = unitOfWork.EmployeeRepository.GetUserByLogin(login, password);
         if (employee != null && employee.Priority == 2)
         {
             Seller._instance = new Seller(employee.Id, employee.FirstName, employee.LastName, employee.Pasition, unitOfWork);
             return(true);
         }
     }
     return(false);
 }
 private Seller(Guid id, string fName, string lName, string position, ISellerUnitOfWork unitOfwork)
     : base(id, fName, lName, position)
 {
     this._order      = new Order();
     this._unitOfWork = unitOfwork;
 }