LINQ-无效的操作异常

Question

请参见下面的代码：

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();
            }
        }

因为用户没有任何应用程序，所以引发了invalidoperationexception。 如何在LINQ uqery中处理此问题？

Answer 1

您可以替换.ToList().Single(); 使用.FirstOrDefault(); 。 如果找不到，则application将为null 。