linq的右外连接？ [英] right outer join in linq?

问题描述

HI，



我们如何在c＃linq中使用右外连接。





这是我的代码

  var  selArticles =（ from  p  in  eLibObj.Publications 
  join    eLibObj.publicationID上的文章等于a.PublicationID 
 
  eLibObj.ArticleReadUnreads.Where（atrxn = > <）中的class =code-sdkkeyword> join  ar  a.ArticleID上的/ span> ampxn.EmployeeID.Equals（iEmployeeID））等于ar.ArticleID 进入 gj 
 来自 newList   gj.DefaultIfEmpty（）
 
 
 
 其中 p.Enabled.Equals（ true ）&& ; a.Published.Equals（ 1 ）&& a.Enabled.Equals（ true ）
 
  select   new  
 {
 ArticleID = a.ArticleID，
 Title = a.Title，
 PublicationID = a.PublicationID，
 PublicationImage = p.ImageName，
 ArticleDate = a.ArticleDate，
 PublicationName = p.Name，
 ArticleTRXNID = newList.ArticleID ==  null ？  0 ：newList.ArticleID，
 
 ArticleLastReadTime = newList.LastReadTime ==  null  ？  new  DateTime（ 1900 ， 1 ，< span class =code-digit> 1 ）：newList.LastReadTime 
}）。ToList（）。OrderByDescending（o = >  o.ArticleLastReadTime）.Take（ 4 ）; 
 

首先我获得所有发表文章，然后想要匹配所有文章empid和读取，并希望从文章中只获得前四个记录。目前发生的情况是它加载所有文章以供发布，并且如果没有数据匹配，则使用readunread表离开外连接，因为左外连接仍然获得前4条记录。

解决方案

< blockquote>你可以尝试这个......根据你的要求安排表格和列名。

 var CategoriesAndProducts = 
来自类别的类别
 join 
类产品中的产品等于product.Category into categoryProducts 
来自categoryProducts.DefaultIfEmpty（）类别
选择新
 {
 product.productname，
 product.productID 
}; 

HI,

how can we use right outer join in c# linq.


here is my code

var selArticles = (from p in eLibObj.Publications
                                      join a in eLibObj.Articles on p.PublicationID equals a.PublicationID

                                      join ar in eLibObj.ArticleReadUnreads.Where(atrxn => atrxn.EmployeeID.Equals(iEmployeeID)) on a.ArticleID equals ar.ArticleID into gj
                                      from newList in gj.DefaultIfEmpty()



                                      where p.Enabled.Equals(true) && a.Published.Equals(1) && a.Enabled.Equals(true)

                                      select new
                                      {
                                          ArticleID = a.ArticleID,
                                          Title = a.Title,
                                          PublicationID = a.PublicationID,
                                          PublicationImage = p.ImageName,
                                          ArticleDate = a.ArticleDate,
                                          PublicationName = p.Name,
                                          ArticleTRXNID = newList.ArticleID == null ? 0 : newList.ArticleID,

                                          ArticleLastReadTime = newList.LastReadTime == null ? new DateTime(1900, 1, 1) : newList.LastReadTime
                                      }).ToList().OrderByDescending(o => o.ArticleLastReadTime).Take(4);

first i get all articles for publication and then want to match all articles with empid and are read and from that want to get only top four records from article. currently what happen that it loads all articles for publication and do left outer join with readunread table if no data match still it gets first 4 records because of the left outer join.

解决方案

you can try this.... arrange table and column name according to your requirement.

var CategoriesAndProducts = 
from category in Categories 
   join product in Products on 
      category equals product.Category into categoryProducts 
from category in categoryProducts.DefaultIfEmpty()
select new 
{ 
   product.productname, 
   product.productID
}; 

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