用where子句求和一个IQueryable列 [英] Sum a IQueryable Column with where clause

问题描述

我有2个查询.一个发现值列大于150,000的地方，我需要输入计数.第二个是总和而不是计数. 计数工作正常，但总和崩溃并提供此错误

I have 2 queries. One to find where Value column is greater than 150,000 and i need the count of entries. The second one is the sum of that rather than count. The Count works perfectly but the sum crashes and provides this error

{强制转换为值类型'System.Decimal'的原因是 物化值为null.结果类型的通用参数 否则查询必须使用可为空的类型.}

{"The cast to value type 'System.Decimal' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type."}

工作代码:

var excessCount = closedDealNonHost.Any() ? closedDealNonHost.Where(x => x.Value > 150000).Count()  : 0;

崩溃代码:

var excessSum = CloseDealNonHost = closedDealNonHost.Any() ? closedDealNonHost.Where(x => x.Value > 150000).Sum(x => x.Value) : 0;

推荐答案

您可以通过在Sum中显式转换为decimal?来解决此问题，例如:

You can solve the issue by explicitly casting to decimal? in Sum like:

var excessSum = CloseDealNonHost = closedDealNonHost.Any() ? closedDealNonHost
                                  .Where(x => x.Value > 150000)
                                  .Sum(x => (decimal?) x.Value) : 0;

此问题是由于从LINQ表达式生成了SQL，在C#端它将尝试返回不能容纳null值的decimal，因此会出错.

The issue is due to generated SQL from LINQ expression, and at C# end it will try to return decimal which can't accommodate a null value, hence the error.

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