如何使用有效的Enumerable.Repeat

Question

我只想在其他代碼位置使用此查詢初始化：

 var post = Enumerable.Repeat(new
            {
                Id = default(int),
                Title = string.Empty,
                Publisher = string.Empty,
                ToUser = string.Empty,
                PublishDate = default(DateTime?),//need to default(DateTime)
                IsFile = default(bool),
                CategoryName = string.Empty,
                status_name = string.Empty,
                Group_name = string.Empty,
                FileSize = default(long?)
            }, 0).ToList();

我已經宣布了一個常見的帖子查詢。 現在我只想讓PublishDate成為default(DateTime?)或default(DateTime) 。

我可以設置為可空，也可以不可空嗎？ 初始化此查詢時，它需要不可為空的日期時間。

- - - - - - - - - - - - -更新 - - - - - - - - - - - - -

在這里，我想要可以約會的日期時間

   post = db.Posts.Where(p => (p.ToUser_id.Equals(user_id) || p.ToUser_id.Equals(null)) && p.User_id != user_id).OrderByDescending(p => p.Sent_Datetime).Select(p => new
                    {
                        Id = p.Id,
                        Title = p.Title,
                        Publisher = db.Users.Where(u => u.Id.Equals(p.User_id)).Select(u => u.First_name + ' ' + u.Last_name).FirstOrDefault(),
                        ToUser = db.Users.Where(u => u.Id.Equals(p.ToUser_id)).Select(u => u.First_name + ' ' + u.Last_name).FirstOrDefault(),
                        PublishDate = p.Sent_Datetime,//nullable date time field
                        IsFile = p.IsFileAttached,
                        CategoryName = db.Categories.Where(c => c.Id.Equals(p.Category_id)).Select(c => c.Category_name).FirstOrDefault(),
                        status_name = db.Status.Where(s => s.Id.Equals(p.status_id)).Select(s => s.status_name).FirstOrDefault(),
                        Group_name = db.Groups.Where(g => g.Id.Equals(p.group_id)).Select(g => g.Group_name).FirstOrDefault(),
                        FileSize = p.TotalFileSize
                    }).FilterForColumn(ColumnName, SearchText).ToList();

在這里，我想要不可空的日期時間

 post = db.Posts.Where(p => p.User_id.Equals(user_id) && p.ToUser_id.Equals(user_id) && p.Sent_Datetime.Equals(null)).OrderByDescending(p => p.Created_datetime).Select(p => new
                    {
                        Id = p.Id,
                        Title = p.Title,
                        Publisher = db.Users.Where(u => u.Id.Equals(p.User_id)).Select(u => u.First_name + ' ' + u.Last_name).FirstOrDefault(),
                        ToUser = db.Users.Where(u => u.Id.Equals(p.ToUser_id)).Select(u => u.First_name + ' ' + u.Last_name).FirstOrDefault(),
                        PublishDate = p.Created_datetime,//non-nullable date time field
                        IsFile = p.IsFileAttached,
                        CategoryName = db.Categories.Where(c => c.Id.Equals(p.Category_id)).Select(c => c.Category_name).FirstOrDefault(),
                        status_name = db.Status.Where(s => s.Id.Equals(p.status_id)).Select(s => s.status_name).FirstOrDefault(),
                        Group_name = db.Groups.Where(g => g.Id.Equals(p.group_id)).Select(g => g.Group_name).FirstOrDefault(),
                        FileSize = p.TotalFileSize
                    }).FilterForColumn(ColumnName, SearchText).ToList();

這第二個給我無法轉換隱式轉換類型...

Answer 1

您可以將其Nullable<DateTime>為Nullable<DateTime> ：

PublishDate = (DateTime?)default(DateTime),

例如，具有一個匿名類型的列表：

var post = Enumerable.Repeat(new
{
    Id = default(int),
    Title = string.Empty,
    Publisher = string.Empty,
    ToUser = string.Empty,
    PublishDate = (DateTime?)default(DateTime),
    IsFile = default(bool),
    CategoryName = string.Empty,
    status_name = string.Empty,
    Group_name = string.Empty,
    FileSize = default(long?)
}, 1).ToList();

這里PublishDate是01.01.0001 00:00:00而不是null 。