Question

我希望将这个SQL语句翻译成一个运行良好的＆amp;高性能的LINQ命令。我已经设法使用分组计数和关键成员进行第一次计数，但不知道如何获得第二次计数。

select main.title, count(details.id) as details, count(messages.id) as messages
from main
 left outer join details on main.id = details.mainid
 left outer join messages on details.id = messages.detailid
group by main.title

这是我到目前为止所做的：

from main in Main
join detail in Details on main.Id equals detail.MainId into j1
from subdetail in j1.DefaultIfEmpty()
group main by main.Title into g
select new { Title = g.Key, Details = g.Count() }

欢迎任何建议！

编辑：24/03/2010 09.41

此查询：

from main in Main
join detail in Details on main.Id equals detail.MainId into j1
from subdetail in j1.DefaultIfEmpty()
join message in Messages on subdetail.Id equals message.DetailId into j2
group main by main.Title into g
select new { Title = g.Key, Details = g.Count() }

生成此SQL语句：

SELECT COUNT(*) AS [Detail], [t0].[Title]
FROM [Main] AS [t0]
LEFT OUTER JOIN [Detail] AS [t1] ON [t0].[Id] = [t1].[MainId]
LEFT OUTER JOIN [Messages] AS [t2] ON [t1].[Id] = [t2].[DetailId]
GROUP BY [t0].[Title]

所以，我差不多完成了！

费边

Answer 1

不会有这样的工作吗？

from main in Main
select new {
    Title = main.Title,
    Details = main.Details.Count(),
    Messages = main.Details.Sum( d => d.Messages.Count())
}

如果您有外键约束，LINQ应自动生成子关系，因此您可以访问与main关联的每个Detail的main.Details，以及与main关联的每个Message的main.Messages。

Linq，双左连接和双重计数

1 个答案: