从多个列中选择最新数据 [英] select most recent data from multiple colums

问题描述

我正在尝试选择数据库中的30个最新条目，但我想从4个不同的表中选择它们。



有没有办法用linq干净快速地做到这一点？



在查询结束时，我想将这些对象存储在列表中。



谢谢提前！

解决方案

这样的事情？

 var items = 
（来自atable中的_tableOne 
加入b中a.ID上的_tableTwo中的b等于b.A_ID 
 a.ID上的_tableThree中的c等于c.A_ID 
加入a _tableFour中的a。 ID等于d.A_ID 
 orderby a.ID降序
选择新的{a.Name，b.B_Field，c.C_Field d.D_Field}）。Take（30）

这样的订购日期对我有用。



您的日期是什么格式？你可能会得到不同的结果。



你的结果是什么顺序？

  var  feedList = 
（（来自 video 在 context.Video 
  orderby  video.Date 降序 
 < span class =code-sdkkeyword> select   new  {TypeID = video.VideoID，CodeID = video.CodeID，Date = video.Date}）。 Take（ 50 ））
 .Union（（ from  comment  in  context.Comment 
  orderby  comment.Date  descending  
 选择  new  {TypeID = comment.CommentID，CodeID = comment.CodeID，Date = comment.Date}）。Take（< span class =code-digit> 50 ））
 .Union（（ from  share 在 context.Share 
  orderby  share.DateTime 降序 
 < span class =code-sdkkeyword> select   new  {TypeID = share.ShareID，CodeID =（ int ？）share.CodeID，Date = share.DateTime}）。Take（ 50 ））
 .Union（（来自事件  context.Event 
  orderby 事件。 CreateDate 
 选择  new  {TypeID = events.EventID，CodeID = events.CodeID，Date = events.CreateDate}） .Take（ 50 ））
 .ToList（）; 
 
 
 
  foreach （ var  f  feedList中的class =code-keyword> 
 {
  var  feed =  new  FeedListItemsContract（）; 
 {
 feed.TypeId = f.TypeID; 
  var  blCode =  new  BLCode（）; 
 feed.CodeName = blCode.GetCodeNameById（（ int ）f.CodeID）; 
 feed.Date = f.Date; 
} 
 result.Add（feed）; 
} 
 
 
  var  resultSorted = result.OrderByDescending（s =  >  s.Date）。ToList（）; 
  return  resultSorted; 

这就是我的意思需要做的才能使它工作..

重要的是每个选择返回相同数量的表格！



感谢您的帮助！

Hi,

I''m trying to select the 30 latest entries in my database, but I want to select them from 4 different tables.

Is there a way to do this clean and quick using linq?

At the end of the query I want to store these objects in a list.

Thanks in advance!

解决方案

Something like this?

var items =
    (from a in _tableOne
    join b in _tableTwo on a.ID equals b.A_ID
    join c in _tableThree on a.ID equals c.A_ID
    join d in _tableFour on a.ID equals d.A_ID
    orderby a.ID descending
    select new { a.Name, b.B_Field, c.C_Field d.D_Field}).Take(30)

Ordering dates like that works for me.

What format are your dates in? You might get different results depending on that.

What order are your results in?

var feedList =
                    ((from video in context.Video
                      orderby video.Date descending
                      select new { TypeID = video.VideoID, CodeID = video.CodeID, Date = video.Date }).Take(50))
                     .Union((from comment in context.Comment
                             orderby comment.Date descending
                             select new { TypeID = comment.CommentID, CodeID = comment.CodeID, Date = comment.Date }).Take(50))
                        .Union((from share in context.Share
                                orderby share.DateTime descending
                                select new { TypeID = share.ShareID, CodeID = (int?)share.CodeID, Date = share.DateTime }).Take(50))
                        .Union((from events in context.Event
                                orderby events.CreateDate
                                select new { TypeID = events.EventID, CodeID = events.CodeID, Date = events.CreateDate }).Take(50))
                               .ToList();



                foreach (var f in feedList)
                {
                    var feed = new FeedListItemsContract();
                    {
                        feed.TypeId = f.TypeID;
                        var blCode = new BLCode();
                        feed.CodeName = blCode.GetCodeNameById((int)f.CodeID);
                        feed.Date = f.Date;
                    }
                    result.Add(feed);
                }


                var resultSorted = result.OrderByDescending(s => s.Date).ToList();
                return resultSorted;

that''s what I needed to do to make it work..
important is that every select returns the same ammount of tables!

thanks for the help!

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