Question

我有一个带有3个连接的LINQ查询和一个抛出空引用错误的分组操作。在下面的查询中（对不起，我很抱歉）如果你跳到'eDTK_PDP_Description'字段，那就是导致问题的那个。我意识到我有最后一个连接的DefaultIfEmpty规范，但我想如果我从该连接中为该字段分配一个值，如果它为null则应该解决问题。我在这做错了什么？谢谢！

Dim UpdateSiebelPDP1 = From j In ( _
                           From PDP In SiebelMultPDPDescNoNull _
                           Group Join Siebel In ProdBase _
                                On PDP.Siebel_PDP_Code Equals Siebel.Siebel_PDP_Code _
                           Into g = Group _
                           From Result In g _
                           Group Join EDTK In eDTKBase _
                                On PDP.Siebel_PDP_Code Equals EDTK.eDTK_PDP_Code _
                           Into h = Group _
                           From Result2 In h _
                           Group Join EDTK2 In EDTKPDPOneDescDet _
                                On PDP.Siebel_PDP_Code Equals EDTK2.PDP_Description _
                           Into i = Group _
                           From Result3 In i.DefaultIfEmpty _
                           Select Result.Siebel_PLI, _
                                  Result.Siebel_PDP_Code, _
                                  Update_DAD_Flag = If(Result.Siebel_DAD_Flag Is Nothing, "Yes", "No"), _
                                  System = "Siebel", _
                                  PDD_PDP_Description = If(Result2.PDD_PDP_Description Is Nothing, _
                                                           "", Result2.PDD_PDP_Description), _
                                  Siebel_PDP_Description = "Multiple", _
                                  eDTK_PDP_Description = If(Result3.PDP_Description Is Nothing, _
                                                            "Multiple", Result3.PDP_Description)) _
                            Group j By j.Siebel_PLI, _
                                       j.Siebel_PDP_Code, _
                                       j.Update_DAD_Flag, _
                                       j.System, _
                                       j.PDD_PDP_Description, _
                                       j.Siebel_PDP_Description, _
                                       j.eDTK_PDP_Description _
                            Into k = Group _
                            Select New With { _
                                    Siebel_PLI, _
                                    Siebel_PDP_Code, _
                                    Update_DAD_Flag, _
                                    System, _
                                    PDD_PDP_Description, _
                                    Siebel_PDP_Description, _
                                    eDTK_PDP_Description}

Answer 1

问题是Result3为空并且您正在尝试访问其上的属性。这就是为什么你的if实际上没有解决问题的原因。如果Result3.SomeField为空，则无法检查Result3是否为空，因为尝试访问会导致NullRefereceException基本上，您需要先检查Result3是否为空关于尝试使用它进行分配。如果是，那么您应该使用一些默认值。我会给出一个大致的想法，虽然它不会是VB因为我不写那些废话：P

   if (Result3 != null)
        eDTK_PDP_Description = Result3.SomeField;
   else
        eDTK_PDP_Description = defaultValue;

您必须自己决定如何将此检查放入查询中。整个事情对我来说有点多，我不知道在Result3为空的情况下你想要分配什么。

具有多个连接的LINQ查询抛出空引用错误

1 个答案: