Question

我得到“无法将null值分配给类型为System.Int32的成员，这是一个非可空的值类型”执行我的空语句的Sum（）时。 ResultView工作正常，但

var r = from v in DataContext.Visits
        join bs in DataContext.BaseContents on v.BaseContentID equals bs.Id
        where (bs.CreatedBy == userId) && (v.DateVisited.Year == workDate.Year) &&
        (v.DateVisited.Month == workDate.Month) && (v.DateVisited.Day == workDate.Day) &&
        (v.IsPreviewed == false) && (bs.ProfileProjectId != null)
        select v;

int? number = r.Sum( v => v.Counter);

或者

var r = from v in DataContext.Visits
        join bs in DataContext.BaseContents on v.BaseContentID equals bs.Id
        where (bs.CreatedBy == userId) && (v.DateVisited.Year == workDate.Year) &&
        (v.DateVisited.Month == workDate.Month) && (v.DateVisited.Day == workDate.Day) &&
        (v.IsPreviewed == false) && (bs.ProfileProjectId != null)
        select v.Counter;

int? number = r.Sum(v);

失败并出现同样的异常。

Answer 1

试试这个（更新）：

int number = r.Sum(v => (int?)v.Counter) ?? 0;

Answer 2

你能包含一些样本数据吗？至少你可以抓住r.ToList（）并手动查看这些值。从我可以看到这看起来它应该工作正常。还要确保v.BaseContentID，bs.Id和v.DateVisited不可为空。（尤其是ID列）引用的任何可空整数都可能导致该异常。不仅仅是选择子句

中的那些

var r = from v in DataContext.Visits
        join bs in DataContext.BaseContents on v.BaseContentID equals bs.Id
        where (bs.CreatedBy == userId) 
            && (v.DateVisited.Date == workDate.Date)
            && (!v.IsPreviewed) 
            && (bs.ProfileProjectId.HasValue)
        select v;

int? number = r.Sum(v => v.Counter);

Answer 3

似乎put && (v.Counter != null)会在运行总和之前过滤掉该值的所有空值。

Linq：int的总和

3 个答案: