帮助与SQL到LINQ转换

Question

有人可以帮助我转换一个SQL查询到LINQ，我很方便linq，但这是有点多，我不能在这里下载linqpad！

select 
    t.*, 
    l.* 
from 
    email_templates t 
left join 
    (select 
     id as email_id, 
     sent_at, 
     sent_by 
    from 
     email_log 
    where 
     id = (select max(id) 
       from email_log 
       where as_at_date = '20100618' 
       group by template_id ) 
    )l 
on t.id = v.template_id 

Answer 1

顺便说一下，我了解您的查询;你需要这样的东西...

var maxId = (from e in email_log 
      where e.as_at_date < new DateTime(2010, 06, 18) 
      group e by e.template_id into grouped 
      select grouped.Max(a => a.id)).First(); 

var selectedEmailLog = from e in email_log 
         where e.id == maxId 
         select new 
         { 
          email_id = e.id, 
          e.sent_at, 
          e.sent_by, 
          e.template_id, 
         }; 

var seletedRows = from t in email_templates 
        join l in selectedEmailLog 
        on t.id equals l.template_id into tls 
        from tl in tls 
        select new 
        { 
         t.id, 
         tl.email_id, 
         tl.sent_at, 
         tl.sent_by, 
        }; 

... LINQ是可组合的，所以你可以打破你的查询成可管理的部分。将查询分解为更小的部分将使其更容易理解。您也可以返回复杂的对象，而不是从数据库创建平面记录呈现。