C# 如果表达式不匹配，LINQ返回表达式

我不确定标题是否能很好地解释这个问题，所以下面是代码。我想返回一个匿名对象来绑定我的网格。在该网格中，我想将用户名更改为全名，但前提是我有与用户名匹配的全名。在下面的查询中，如果userModels中存在CreatedUsername，我将获得CreatedFullname。如果它不存在，那么我就根本得不到记录。我所做的是获取记录，如果userModels中有UserFullname，则显示UserFullname，如果没有，则返回x.CreatedUsername

var inf = (from ev in db.Events
       where (ev.StartDate >= beginDate && ev.StartDate <= endDate)
       orderby ev.StartDate descending
       select new
       {
           EventID = ev.EventID,
           EventTitle = ev.Title,
           EventDate = ev.StartDate,
           StudentCount = ev.EventStudents.Count(),
           CreatedUsername = ev.CreatedUsername
           }).AsEnumerable().Select(x => new {EventID = x.EventID,
                                    EventTitle = x.EventTitle,
                                    EventDate = x.EventDate,
                                    StudentCount = x.StudentCount,
                                    CreatedUsername = x.CreatedUsername,
                                    CreatedFullname = 
                                      userModels.Where(u => u.Username == x.CreatedUsername).FirstOrDefault().UserFullName
            });

var inf=（来自以db.Events表示的ev）
其中（ev.StartDate>=beginDate&&ev.StartDate new{EventID=x.EventID，
EventTitle=x.EventTitle，
EventDate=x.EventDate，
StudentCount=x.StudentCount，
CreatedUsername=x.CreatedUsername，
CreatedFullname=
其中（u=>u.Username==x.CreatedUsername）.FirstOrDefault（）.UserFullName
});

userModels是一个自定义对象，具有用户名、UserFullname、Department等。它是根据beginDate和endDate在pageload上从ActiveDirectory收集的。

您可以执行以下操作：

CreatedFullname = 
    userModels.Where(u => u.Username == x.CreatedUsername)
              .Select(x => x.UserFullName)
              .FirstOrDefault() ?? x.CreatedUsername

或者这个：

var inf = 
    (from x in
        (from ev in db.Events
         where (ev.StartDate >= beginDate && ev.StartDate <= endDate)
         orderby ev.StartDate descending
         select new
         {
             EventID = ev.EventID,
             EventTitle = ev.Title,
             EventDate = ev.StartDate,
             StudentCount = ev.EventStudents.Count(),
             CreatedUsername = ev.CreatedUsername
         })
         .AsEnumerable()
     let model = userModels.FirstOrDefault(u => u.Username == x.CreatedUsername)
     select new 
     {
         EventID = x.EventID,
         EventTitle = x.EventTitle,
         EventDate = x.EventDate,
         StudentCount = x.StudentCount,
         CreatedUsername = x.CreatedUsername,
         CreatedFullname = (model != null)
             ? x.modelUserFullName 
             : x.CreatedUsername
     });

var-inf=
（从x开始）
（以db.事件为单位的ev）
其中（ev.StartDate>=beginDate&&ev.StartDate u.Username==x.CreatedUsername）
选择新的
{
EventID=x.EventID，
EventTitle=x.EventTitle，
EventDate=x.EventDate，
StudentCount=x.StudentCount，
CreatedUsername=x.CreatedUsername，
CreatedFullname=（模型！=null）
？x.modelUserFullName
：x.CreatedUsername
});