本篇内容主要讲解“强制转换为值类型“System.Double”失败的原因”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“强制转换为值类型“System.Double”失败的原因”吧!
计算
安全
数据库
网络和加速
企业服务
foreach (var item in entityList)
{
ChannelReportDto channelReportDto = new ChannelReportDto();
channelReportDto.Id = item.Id;
channelReportDto.YueziCenterId = item.YueziCenterId;
channelReportDto.YueziCenterName = item.YueziCenterName;
channelReportDto.ChannelName = item.ChannelName;
channelReportDto.SumProfitAmount = OrderServiceProjectresult.Where(w => w.ChannelId == item.Id && w.IsDeleted == false).Select(s => s.SumProfitAmount).Sum();
channelReportDto.SettleProfitAmount = OrderServiceProjectresult.Where(w => w.ChannelId == item.Id && w.IsSettlement == true).Select(s => s.SumProfitAmount).Sum();
channelReportDto.NoSettleProfitAmount = OrderServiceProjectresult.Where(w => w.ChannelId == item.Id && w.IsSettlement == false).Select(s => s.SumProfitAmount).Sum();
list.Add(channelReportDto);
}这样写的时候 就报了这个错 The cast to value type 'System.Double' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type.
主要原因是没有适合查询条件的行 去计算，
所以改成以下写法就OK
foreach (var item in entityList)
{
ChannelReportDto channelReportDto = new ChannelReportDto();
channelReportDto.Id = item.Id;
channelReportDto.YueziCenterId = item.YueziCenterId;
channelReportDto.YueziCenterName = item.YueziCenterName;
channelReportDto.ChannelName = item.ChannelName;
channelReportDto.SumProfitAmount = OrderServiceProjectresult.Where(w => w.ChannelId == item.Id && w.IsDeleted == false).Sum(s =>(double?)s.SumProfitAmount)??0.00;
channelReportDto.SettleProfitAmount = OrderServiceProjectresult.Where(w => w.ChannelId == item.Id && w.IsSettlement == true).Sum(s => (double?)s.SumProfitAmount) ?? 0.00;
channelReportDto.NoSettleProfitAmount = OrderServiceProjectresult.Where(w => w.ChannelId == item.Id && w.IsSettlement == false).Sum(s => (double?)s.SumProfitAmount) ?? 0.00;
list.Add(channelReportDto);
}到此，相信大家对“强制转换为值类型“System.Double”失败的原因”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
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原文链接：https://my.oschina.net/u/2494395/blog/3102204
