LINQ-无效的操作异常

Question

Please see the code below:

static MapperConfiguration config = new MapperConfiguration(cfg =>
        {
            cfg.CreateMap<DataObjects.Application, BusinessObjects.Application>();
        });

        public BusinessObjects.Application getApplication(string UserID)
        {
            using (CreditCardPreQualificationEntities CreditCardPreQualificationDatabase = new CreditCardPreQualificationEntities())
            {
                //DataObjects.Application application = CreditCardPreQualificationDatabase.Applications.FirstOrDefault(c => c.userID== UserID);
                BusinessObjects.Application application = CreditCardPreQualificationDatabase
                    .Applications
                    .ProjectTo<BusinessObjects.Application>(config)
                    .Where(c => c.UserID == UserID)
                    .ToList().Single();
                return application;
                //return new BusinessObjects.Application();
            }
        }

An invalidoperationexception is thrown because the user does not have any applications. How can I handle this in the LINQ uqery?

Answer 1

You can replace .ToList().Single(); with .FirstOrDefault(); . Then application will be null if not found.