如何在这个LINQ查询中获取总和?

myDataContext.Questions
  .OrderByDescending(q => q.Votes.Select(v => v.VoteValue).Sum())

在查询理解中(未选中):

from q in myDataContext.Questions
order q by 
(
  from v in q.Votes
  select v.VoteValue
).Sum() descending
select q;

这主要取决于你的数据,但这里有一个小样本:

XElement xdoc=XElement.Parse(@"
  <root>
    <question name=""A"">
      <vote type=""up"" />
      <vote type=""down"" />
    </question>
    <question name=""B"">
      <vote type=""up"" />
      <vote type=""up"" />
    </question>
    <question name=""C"" />
  </root>
  ");

var result=
  from q in xdoc.Elements("question")
  let votes=q.Elements("vote").Count(v=>v.Attribute("type").Value=="up")
  orderby votes descending
  select new
  {
    Name=q.Attribute("name").Value,
    Votes=votes
  };

foreach (var r in result)
{
  Console.WriteLine(r.Name+" "+r.Votes);
}

既然你在使用EntitySet,我猜它是linq2sql?假设您有正确设置的引用并有投票权。问题属性:

(from v in dc.Votes
where v.IsUpVote // v.Vote == 1 (??)
group v by v.Question into q
select new { Question = q.Key, UpVotes = q.Count() }).OrderByDescending(e => e.UpVotes);

我在这里收集count()实际上是你想要的?sum()将产生相同的结果,但可能没有意义(?)