摘要： 表A中有一列StorageByte(int, not null),求和 A.Where(a => a.JobId ==@jodid).Select(c=>c.StorageByte).Sum() 如果这个@jodid不存在,程序会报InvalidOperationException：The null value cannot be assigned to a member with type System.Int32 which is a non-nullable value type. 阅读全文