jion 左表 比 右表 少几行数据

       var dtDeviceDataSum = (from a in dtDeviceDataSameSum
                                           join b in dtDeviceDataDiffSum
                                           on (Convert.ToDateTime(a.currtime).Day)
                                            equals (Convert.ToDateTime(b.currtime).Day)
                                           into c
                                           from o in c.DefaultIfEmpty()
                                           select new
                                           {
                                               dateType = Convert.ToDateTime(a.currtime).Day,
                                               currQty = System.DBNull.Value.Equals(a.currElectQty) ? 0 : a.currElectQty,
                                               beforeQty = o.currElectQty.HasValue ? o.currElectQty : decimal .Zero 
                                           }).ToList();

dtDeviceDataDiffSum比少dtDeviceDataSameSum几行数据，
所以这个beforeQty是有可能为null的，我这么写按理说没错啊，
为什么一直报“未将对象引用到实例”  。

3 个解决方案

#1

非常简单：

 beforeQty =(o!=null && o.currElectQty.HasValue ) ? o.currElectQty.Value : decimal .Zero 

#2

该回复于2017-05-01 00:01:46被版主删除

#3

用之前，先判断下是否为空