.net - linq to sql将这个查询翻译成: "select *"?格式是不是效率低下

Question

我对 Linq to SQL 还不是很熟悉，但让我印象深刻的是:

var articles = 
  (from a in DB.Articles
  where 
  a.ArticleId == ArticleId.Question &&
  a.DeletedAt == null &&
  a.Votes >= minVotes
  orderby a.UpdatedAt descending
  select a).
  Take(maxarticles);

翻译成这样:

string query = 
  "select top 10 * from articles
  where 
  ArticleId = 1 and 
  DeletedAt is null and 
  Votes >= -5
  order by UpdatedAt desc";

令我印象深刻的是，linq to sql 愿意使用“select *”类型的查询清理所有内容。 这不是很低效吗？

linq to sql为什么要这样做？

Answer 1

如果您想选择较少的列，则必须在 linq 查询中使用投影。

var articles = (from a in DB.Articles
    where a.ArticleId == ArticleId.Question 
        && a.DeletedAt == null 
        && a.Votes >= minVotes
    orderby a.UpdatedAt descending
    select new 
    {
       a.ArticleId,
       a.Votes
    })
    .Take(maxarticles);

像上面这样的操作会转换成如下所示的 SQL...

select top 10 
         ArticleId,
         Votes
from     articles
where    ArticleId = 1 
         and DeletedAt is null
         and Votes >= -5
order by UpdatedAt desc