如果表达式不匹配，LINQ返回表达式

本文关键字：表达式 返回 LINQ 不匹配 如果 | 更新日期: 2023-09-27 18:17:22

我不确定标题是否很好地解释了这个问题，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，我希望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，如果在userModels中存在CreatedUsername，我将获得CreatedFullname。如果它不存在，那么我根本不会得到记录。我想要的是得到的记录，显示UserFullname，如果它是可用的userModels，如果它不是我想返回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
            });

userModels是一个自定义对象，它有Username, UserFullname, Department等。它是在页面加载时根据beginDate和endDate从ActiveDirectory收集的

如果表达式不匹配，LINQ返回表达式

你可以这样做:

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

或:

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
     });

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