Linq的奇怪行为

Question

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

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，它将返回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();

现在我在查询中对userid进行硬编码，然后再次返回两个结果：

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？

如果是这样，请确保.Where(up => up.UserID.HasValue && up.UserID.Value == userID)

我曾经有过类似于可以为空的日期时间

Answer 2

您是否尝试在变量中分配相同的硬编码值？我的猜测是你的数据中没有找到变量中的值，也就是说你确定变量名是正确的。