public ServiceResult ChangeDrpParticipation(Guid stockId, bool participation)
        {
            if (_Portfolio == null)
            {
                return(ServiceResult <List <Holding> > .NotFound());
            }

            var holding = _Portfolio.Holdings[stockId];

            if (holding == null)
            {
                return(ServiceResult.NotFound());
            }

            _Portfolio.ChangeDrpParticipation(stockId, participation);

            return(ServiceResult.Ok());
        }