c# - 如果第二个或第三个表为空，LINQ Join 不返回结果

Question

我有三个表:

Module_Articles_Articles
Module_Articles_Categories
Module_Articles_Comments

我想在转发器中显示我的文章我的查询:

var articles =
                (from a in context.Module_Articles_Articles
                 join c in context.Module_Articles_Categories on a.CategoryID equals c.CategoryID
                 join co in context.Module_Articles_Comments on a.ArticleID equals co.ArticleID
                 where a.IsDraft == false
                 orderby a.ArticleID descending
                 select new
                 {
                     a.ArticleID,
                     a.ArticleTitle,
                     a.ArticleContent,
                     a.Image,
                     a.Sender,
                     a.SentDate,
                     a.Summary,
                     a.Likes,
                     a.Dislikes,
                     a.Tags,
                     a.PostMode,
                     c.CategoryID,
                     c.CategoryTitle,
                     AcceptedCommentsCount = 
                     (from com in context.Module_Articles_Comments where com.ArticleID == a.ArticleID && com.Status select com)
                     .Count(),
                     DeniedCommentsCount =
                     (from com in context.Module_Articles_Comments where com.ArticleID == a.ArticleID 
                          && com.Status == false select com)
                     .Count()
                 }).ToList();

但是当 Module_Articles_Categories 或 Module_Articles_Comments 为空时，我的查询什么都不返回!我的代码是真的吗？如果没有，我该怎么做？

Answer 1

你想要一个外部连接，这可以通过简单地添加 .DefaultIfEmpty()

在这样的查询中完成

from a in context.Module_Articles_Articles
join c in context.Module_Articles_Categories on a.CategoryID equals c.CategoryID into ca
from c in cs.DefaultIfEmpty()
join co in context.Module_Articles_Comments on a.ArticleID equals co.ArticleID into com
from co in com.DefaultIfEmpty()
where a.IsDraft == false
orderby a.ArticleID descending
select new ...