使用多列将 linq 加入数据集查询

Question

您好，我正在尝试加入 2 个数据表，左侧的一个包含 3 个不同的列作为主键，另一个包含与外键相同的列，这是左侧的数据表图像：

正确的 DataTable Imge 就是这个：

这是我正在尝试使用的代码，但没有返回任何内容，它应该是

var query5 =
        from ChanToNGrsToNgrDAnWal in chanToNGrsToNgrDAnWal.AsEnumerable()
        join Node in node.AsEnumerable() 
            on new { 
                 A = ChanToNGrsToNgrDAnWal.Field<int?>("diffusers_Id"), 
                 B = ChanToNGrsToNgrDAnWal.Field<int?>("analogs_Id"), 
                 C = ChanToNGrsToNgrDAnWal.Field<int?>("wallstats_Id") }
            equals new { 
                 A = Node.Field<int?>("diffusers_Id"), 
                 B = Node.Field<int?>("analogs_Id"), 
                 C = Node.Field<int?>("wallstats_Id") 
            }                  
        select new
        {
            channel_Id = ChanToNGrsToNgrDAnWal.Field<int?>("channel_Id"),
            number = ChanToNGrsToNgrDAnWal.Field<string>("number"),
            nodeGroups_Id = ChanToNGrsToNgrDAnWal.Field<int>("nodeGroups_Id"),
            analogNodeSerial = ChanToNGrsToNgrDAnWal.Field<string>("analogNodeSerial"),
            diffuserNodeSerial = ChanToNGrsToNgrDAnWal.Field<string>("diffuserNodeSerial"),
            wallStatNodeSerial = ChanToNGrsToNgrDAnWal.Field<string>("wallStatNodeSerial"),
            diffusers_Id = ChanToNGrsToNgrDAnWal.Field<int?>("diffusers_Id"),
            analogs_Id = ChanToNGrsToNgrDAnWal.Field<int?>("analogs_Id"),
            wallstats_Id = ChanToNGrsToNgrDAnWal.Field<int?>("wallstats_Id"),
            typeCode = Node.Field<string>("typeCode"),
            node_Id = Node.Field<int?>("node_Id")

        };

谁能告诉我为什么会这样或者我写的查询是错误的，请你们帮帮我。

Answer 1

根据您的示例数据，您在此处没有任何匹配项（零与空值不匹配）。如果由于您的应用程序的逻辑而这没问题，那么您可以将字段的值转换为int 而不是Nullable<int>。在这种情况下，将为DbNull 单元格提供默认值（零）：

    on new { 
         A = ChanToNGrsToNgrDAnWal.Field<int>("diffusers_Id"), 
         B = ChanToNGrsToNgrDAnWal.Field<int>("analogs_Id"), 
         C = ChanToNGrsToNgrDAnWal.Field<int>("wallstats_Id") 
    }
    equals new { 
         A = Node.Field<int>("diffusers_Id"), 
         B = Node.Field<int>("analogs_Id"), 
         C = Node.Field<int>("wallstats_Id") 
    }