C# linq group by 在同一实体中的不同键上

Question

我已经研究了一段时间了，就是搞不懂。我是 Linq、C# 和这些 Lambda 的新手。

我想做的是根据每个实体的两个属性对实体进行分组。这是一个消息实体:

Message
{
int UserId; //The user generating the message
int UserIdTo; //The receiver of the message
|...| // Other stuff 
}

所以，我希望这些 UserId=5, UserIdTo=6 和 UserId=6, UserIdTo=5 在同一个组中。

这是我的开始:

var groupList = (from m in db.Messages
                             where m.UserId == userId || m.UserIdTo == userId
                             join u in db.Users on m.UserId equals u.UserId
                             join w in db.Users on m.UserIdTo equals w.UserId
                             orderby m.MessageTimestamp descending
                             select new DomMessage
                             {
                                 MessageId = m.MessageId,
                                 MessageContent = m.MessageContent,
                                 MessageTimestamp = m.MessageTimestamp,
                                 UserId = m.UserId,
                                 UserIdTo = m.UserIdTo,
                                 ScreenName = u.ScreenName,
                                 ScreenName2 = w.ScreenName
                             }).GroupBy(m=>m.UserId == userId)
                             .ToList();

这是按 UserId 进行分组的第一步，但我一直在尝试扩展它，以便在结果组中的任何 UserId 值等于 UserIdTo 的地方将其添加到该组中？

编辑:我需要将结果放入列表，因为我还需要用它做其他事情...

谢谢!

Answer 1

试试这个:

var payload = new[] 
        {
            new{ To = 1, From = 2, Message = "msj1" },
            new{ To = 1, From = 2, Message = "msj2" },
            new{ To = 2, From = 1, Message = "msj3" },
            new{ To = 4, From = 1, Message = "msj4" },
            new{ To = 1, From = 3, Message = "msj5" }
        };


        var groupped = payload.Select(x => new { Key = Math.Min(x.To, x.From) + "_" + Math.Max(x.To, x.From), Envelope = x }).GroupBy(y => y.Key).ToList();

        foreach (var item in groupped)
        {
            Console.WriteLine(String.Format(@"Group: {0}, messages:", item.Key));

            foreach (var element in item)
            {
                Console.WriteLine(String.Format(@"From: {0} To: {1} Message: {2}", element.Envelope.From, element.Envelope.To, element.Envelope.Message));
            }
        }