将TSql命令转换为LINQ，错误为“无法转换为LINQ to Entities存储表达式”

Question

以下命令在SQL Server中返回预期的输出：

select count(*) As CountField 
from
    (select Eductionals.UserID , Max(Eductionals.MaghtaeID) As IDmaghta
from Eductionals 
    group by Eductionals.UserID) Temptable
        inner join MaghtaeTahsilis ON
         Temptable.IDmaghta = MaghtaeTahsilis.ID
        where Temptable.IDmaghta = 3 /* any number */
        group by Temptable.IDmaghta

我试图将以上代码转换为LINQ：

    var maghtae = _maghtaeTahsili.Where(z => z.Code == MaghtaeCode).FirstOrDefault();
    return _eductional.GroupBy(z=> z.UserID).Max().Where(z => z.MaghtaeID == maghtae.ID).Select(z => z).Count();

运行后，遇到以下错误：

  

“ IGrouping”不包含针对   'MaghtaeID'，并且没有可访问的扩展方法'MaghtaeID'接受   可以找到类型为“ IGrouping”的第一个参数   （您是否缺少using指令或程序集引用？）