Question

我必须将以下表达式从VB.NET转换为C＃：

Dim z = From d In db.GPSdevice
    Where d.CompanyId = currentuser.CompanyId And d.Type = "Trailer"
    Order By d.ListOrder Descending
    Group d By Geofence = d.GeofenceLocation Into g = Group, Count()
    Order By Count Descending

我对Group By部分感到困惑......

Answer 1

字面翻译

var z = from d in db.GPSdevice
        where d.CompanyId == currentuser.CompanyId && d.Type == "Trailer"
        orderby d.ListOrder descending
        group d by d.GeofenceLocation into g
        orderby g.Count() descending
        select new { Geofence = g.Key, g = (from g2 in g select g2), Count = g.Count() };

但这并不会导致与原始VB查询完全相同的类型。

这是一个更多（过早？）优化的版本，它确实产生相同的类型：

var z2 = (from d in db.GPSdevice
         where d.CompanyId == currentuser.CompanyId && d.Type == "Trailer"
         group d by d.GeofenceLocation into g
         select new { Geofence = g.Key, g = (from g2 in g orderby g2.ListOrder descending select g2).ToArray(), Count = g.Count() }).OrderByDescending(g => g.Count);

Answer 2

一旦掌握了语法，就应该非常直接。你会做类似

的事情

将“records.property”的“记录”分组到groups_set

然后你会做一个选择来执行获取你的密钥（按属性分组）和相关的计数。您的linq语句应如下所示：

from d in db.GPSdevice
where d.CompanyId == currentuser.CompanyId && d.Type == "Trailer"
group d by d.GeofenceLocation into g 
select new { GeofenceLocation = g.Key, Count = g.Count() }

Answer 3

在GroupBy之后使用anonymous types，这样您就可以OrderBy群组g Count()。

.Select(g => new { Group = g.Key.GeofenceLocation, Count = g.Count() })

使用LINQ流利语法：

var z = db.GPSdevice
          .Where(d => d.CompanyId == currentuser.CompanyId && d.Type == "Trailer")
          .OrderByDescending(d => d.ListOrder)
          .GroupBy(g => g.GeofenceLocation)
          .Select(g => new { Group = g.Key.GeofenceLocation, Count = g.Count() })
          .OrderByDescending(g => g.Count)

注意：

g.Key引用d对象
g.Count是指匿名类型的Count，而不是LINQ＆＃39; Count()。

将VB.NET Group By表达式转换为C＃

3 个答案: