Question

我正在尝试在“用户”页面上创建一个Feed，如果用户最近喜欢某些内容，创建了一个项目，在帖子上发表了评论，那么它将会显示。我将如何操作？我正在考虑从数据库中获取不同信息的对象列表，然后按日期排序，但我无法正确订购代码。

Answer 1

怎么样：

var feed = db.Likes
    .Where(like => like.UserID == currentUserID)
    .Where(like => like.CreatedAt > createdSince)
    .OrderByDescending(like => like.CreatedAt)
    .Select(like => new {
        Type = "like",
        CreatedAt = like.CreatedAt
    })
    .Concat(db.Comments
        .Where(comment => comment.UserID == currentUserID)
        .Where(comment => comment.CreatedAt > createdSince)
        .OrderByDescending(comment => comment.CreatedAt)
        .Select(comment => new {
            Type = "comment",
            CreatedAt = comment.CreatedAt
        })
    );

根据需要添加更多Concat语句，只要它们投射到相同的结构（anon或实际类），就可以将它们合并到一个列表中。

如果您不喜欢有一个巨大的陈述，并且有一个类来存储项目（例如Feed），那么选择第一个并执行.ToList()，那么您将拥有{{1}您可以为要包含的每个额外项目调用List<Feed>。

只需对每个列表进行排序并提供额外的过滤器。将它们合并为一个后，您就可以对合并列表进行排序。

Answer 2

好吧，我最终做的事情就是这样：

public class UserFeed
{
    public string Type { get; set; }
    public int Reference_Id { get; set; }
    public int Comic_Id { get; set; }
    public int Chapter_Id { get; set; }
    public int Page_Id { get; set; }
    public int User_Id { get; set; }
    public string Title { get; set; }
    public string Text { get; set; }
    public decimal Rating { get; set; }
    public string Image { get; set; }
    public DateTime Date { get; set; }
}

 List<UserFeed> userFeed = new List<UserFeed>();
 userFeed.AddRange(user.SelectMany(i => i.UserFavorites).Select(i => new UserFeed { Type = "UserFavorite", Reference_Id = i.UserFavorite_Id, Comic_Id = i.Comic_Id, Title = i.Comic.Title, Image = i.Comic.ComicImage, Date = i.DateFavorited }).OrderByDescending(i => i.Date).Take(6));
 userFeed.AddRange(Comics.SelectMany(i => i.ComicReviews).Select(i => new UserFeed { Type = "ComicReview", Reference_Id = i.ComicReview_Id, Comic_Id = i.Comic_Id, Title = i.Comic.Title, Text = i.Text, Rating = i.ComicRating.Rating, Image = i.Comic.ComicImage, Date = i.DatePublished }).OrderByDescending(i => i.Date).Take(6));
 userFeed.AddRange(Comics.SelectMany(i => i.Chapters).Select(i => new UserFeed { Type = "Chapter", Reference_Id = i.Chapter_Id, Comic_Id = i.Comic_Id, Title = i.Title, Image = i.Comic.ComicImage, Date = i.DatePublished }).OrderByDescending(i => i.Date).Take(6));
 userFeed.AddRange(Comics.SelectMany(i => i.Chapters.SelectMany(j => j.Pages)).Select(i => new UserFeed { Type = "Page", Reference_Id = i.Page_Id, Chapter_Id = i.Chapter_Id, Title = i.Title, Image = i.PageImage, Date = i.DatePublished }).OrderByDescending(i => i.Date).Take(6));

创建按日期排序的事件源

2 个答案: