private IEnumerable<SubjectSelectorSubjectGroup> GetSubjectList()
{
    User user = db.Users.Find(WebSecurity.CurrentUserId);
    return db.requiredSubjects.Where(r => !r.Subject.Name.Contains("Home"))
                              .GroupBy(r => r.Subject)
                              .OrderByDescending(r => r.Count())
                              .Select(r => new SubjectSelectorSubjectGroup()
                              {
                                  SubjectId = r.Key.SubjectId,SubjectName = r.Key.Name,IsInFavourites = HttpContext.Current.Request.IsAuthenticated &&
                                                  (user.Elective1 != null && user.Elective1.SubjectId == r.Key.SubjectId ||
                                                   user.Elective2 != null && user.Elective2.SubjectId == r.Key.SubjectId ||
                                                   user.Elective3 != null && user.Elective3.SubjectId == r.Key.SubjectId),Occurrences = r.Count()
                              });
}

当用户未登录时,此函数中的用户变量为null.这不应该是一个问题,因为短路布尔评估应该处理这个问题.问题是,它没有！而是抛出System.NullReferenceException.

当用户为null时,HttpContext.Current.Request.IsAuthenticated返回false.我通过注释引用用户变量的括号部分来检查这一点,然后表达式正确评估.

有谁知道为什么Linq to sql在这种情况下试图取消引用用户变量时它实际上不应该是必要的？有没有人解决这个问题？