LINQ查询可空总和 [英] Linq query with nullable sum

问题描述

 从我Db.Items
选择新VotedItem
{
    ITEMID = i.ItemId，
    点=（从Db.Votes v
              其中，b.ItemId == v.ItemId
              选择v.Points）.SUM（）
}
 

我得到这个查询，但如果没有得票数与异常发现失败：

 的空值不能分配给类型System.Int32一个成员是一个非空的值类型。
 

我认为它的，因为总和返回一个int，而不是一个可空INT，给人总和诠释？作为输入，只给出了同样的错误，很可能导致总和仅workes的整数。

有什么好的解决方法呢？

解决方案

 从我Db.Items
选择新VotedItem
{
    ITEMID = i.ItemId，
    点=（从Db.Votes v
              其中，b.ItemId == v.ItemId
              选择v.Points？ 0）.SUM（）
}
 

编辑 - 确定这个什么......（再次拍摄，因为我不知道你的模型...）：

 从我Db.Items
选择新VotedItem
{
    ITEMID = i.ItemId，
    点=（从Db.Votes v
              其中，b.ItemId == v.ItemId）
              的.sum（V =＆GT; v.Points）
}
 

from i in Db.Items
select new VotedItem
{
    ItemId = i.ItemId,
    Points = (from v in Db.Votes
              where b.ItemId == v.ItemId
              select v.Points).Sum()
}

I got this query, however it fails if no votes are found with exception:

The null value cannot be assigned to a member with type System.Int32 which is a non-nullable value type.

I assume its because sum returns an int and not a nullable int, giving sum a int? as input only give the same error, probably cause sum only workes on ints.

Any good workaround for this?

解决方案

from i in Db.Items
select new VotedItem
{
    ItemId = i.ItemId,
    Points = (from v in Db.Votes
              where b.ItemId == v.ItemId
              select v.Points ?? 0).Sum() 
}

EDIT - ok what about this... (Shooting again since I don't know your model...):

from i in Db.Items
select new VotedItem
{
    ItemId = i.ItemId,
    Points = (from v in Db.Votes
              where b.ItemId == v.ItemId)
              .Sum(v => v.Points) 
}

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