本文介紹了總和可為空的 Linq 查詢的處理方法，對大家解決問題具有一定的參考價值，需要的朋友們下面隨著小編來一起學習吧！
問題描述
限時送ChatGPT賬號..
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()
}
我收到了這個查詢，但是如果沒有發(fā)現(xiàn)異常投票，它就會失敗:
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.
我假設它是因為 sum 返回一個 int 而不是一個可為空的 int，所以給 sum 一個 int?由于輸入只給出相同的錯誤，可能導致 sum 僅適用于整數(shù).
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.
有什么好的解決方法嗎?
Any good workaround for this?
推薦答案
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()
}
編輯 - 好吧，這個怎么樣...(再次拍攝，因為我不知道你的型號...):
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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