总和可为空的 Linq 查询

Linq query with nullable sum(总和可为空的 Linq 查询)

问题描述

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()
}

我收到了这个查询，但是如果没有发现异常投票，它就会失败:

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.

我假设它是因为 sum 返回一个 int 而不是一个可为空的 int，所以给 sum 一个 int?由于输入只给出相同的错误，可能导致 sum 仅适用于整数.

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.

有什么好的解决方法吗?

Any good workaround for this?

推荐答案

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() 
}

编辑 - 好吧，这个怎么样...(再次拍摄，因为我不知道你的型号...):

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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