何在 EF 查询中将 Uint 转换为 Nullable Int

Question

我正在尝试将 Uint(i_Customer) 转换为 Nullable Int(i_Customer) ID，因为一个接受 Null 值而另一个 ID 不支持。 父表是 Customer(i_Customer)，子表是 Fault(i_customer)。两者，我都在 EF 查询中加入它们以获得结果。但是有一个非常令人不安的nullreferenceexception was unhandled by user code 异常。我该如何解决？

这是 EF 查询：

if (servicelevel == 3)
            {
                result = (from s in res
                          join cInfo in custInfo on 
                          s.fault.i_customer equals Convert.ToInt32((int?)cInfo.customers.i_Customer) 
                          where (s.fault.resolved == null) || (s.tasks.assignedto == agent)
                          orderby s.fault.ispriority descending, s.fault.logtime ascending
                          select new ActiveFaultResult()
                          {   Company_Name = cInfo.customers.Company_Name,
                                  //replies = replies,
                                  idFaults = s.fault.idFaults,
                                  hashvalue = s.fault.hashvalue,
                                  responsible = s.fault.responsible,
                                  logtime = s.fault.logtime,
                                  isinternal = s.fault.isinternal,
                                  ispriority = s.fault.ispriority

                           }).ToList<ActiveFaultResult>();

                //  var limitresult = result.Take(50);
                return result;
            }

Answer 1

普通演员就可以了

s.fault.i_customer equals (int?)cInfo.customers.i_Customer

或者试试这个

s.fault.i_customer ?? 0 equals cInfo.customers.i_Customer

Answer 2

您需要使用 DefaultIfEmpty() 来提供外连接，以便它可以处理空值。请参见下面的示例：

result = (from s in res
         join cInfo in custInfo on s.fault.i_customer equals (int)cInfo.customers.i_Customer into A
         from cInfo in A.DefaultIfEmpty()
         where (s.fault.resolved == null) || (s.tasks.assignedto == agent)
         orderby s.fault.ispriority descending, s.fault.logtime ascending
         select new ActiveFaultResult()
         {
                Company_Name = cInfo == null? String.Empty: cInfo.customers.Company_Name,
                idFaults = s.fault.idFaults,
                hashvalue = s.fault.hashvalue,
                responsible = s.fault.responsible,
                logtime = s.fault.logtime,
                isinternal = s.fault.isinternal,
                ispriority = s.fault.ispriority
         }).ToList<ActiveFaultResult>();
return result;