linq - Linq 的奇怪行为

Question

我有一个运行着 Sql Server CE 3.5 数据库的 Windows 窗体应用程序 (.NET 4.0)，我通过 EF 连接访问它。

这是我的初始查询，它返回两个结果:

var list = db.UserPresentation
                         .Select(up => new
                         {
                             UserPresentationID = up.UserPresentationID,
                             PresentationName = up.PresentationName,
                             DateRequested = up.DateRequested,
                             Edit = string.Empty,
                             Delete = string.Empty,
                             Download = string.Empty
                         })
                         .OrderByDescending(up => up.DateRequested)
                         .ToList();

现在我引入了一个外部变量和一个 where 子句，它返回零结果。如果我在 LinqPad 中运行相同的代码，它会返回 2 个结果。

 int userID = 2;

            // load list of user presentations
            var list = db.UserPresentation
                         .Where(up => up.UserID == userID)
                         .Select(up => new
                         {
                             UserPresentationID = up.UserPresentationID,
                             PresentationName = up.PresentationName,
                             DateRequested = up.DateRequested,
                             Edit = string.Empty,
                             Delete = string.Empty,
                             Download = string.Empty
                         })
                         .OrderByDescending(up => up.DateRequested)
                         .ToList();

现在我在查询中硬编码 userid，它再次返回两个结果:

var list = db.UserPresentation
                         .Where(up => up.UserID == 2)
                         .Select(up => new
                         {
                             UserPresentationID = up.UserPresentationID,
                             PresentationName = up.PresentationName,
                             DateRequested = up.DateRequested,
                             Edit = string.Empty,
                             Delete = string.Empty,
                             Download = string.Empty
                         })
                         .OrderByDescending(up => up.DateRequested)
                         .ToList();

我真的很难过。知道这里发生了什么吗？

Answer 1

UserID 可以为空吗？

如果是，请务必执行 .Where(up => up.UserID.HasValue && up.UserID.Value == userID)

我曾经有过类似的可空日期时间