NHibernate SelectMany在GroupBy引发“无法识别查询源”之后

Question

我正在尝试将SQL脚本转换为NHibernate Linq语句。但是我并没有走得很远：

var subQuery = selected.SelectMany(s => s.Attributes)
    .GroupBy(a => a.AttributeDefinition.Id)
    .SelectMany(g => g)
    .ToList();

此代码引发异常：

  

无法识别查询源：ItemName = g，ItemType = System.Linq.IGrouping'2 [System.Int32，DomainLayer.ProductManagement.SetPoints.SetPointAttribute]，表达式=来自IGrouping'2 g in {来自SetPoint x in值（NHibernate.Linq.NhQueryable'1 [DomainLayer.ProductManagement.SetPoints.SetPoint]）其中（[x] .Product.Id == 3）其中（[x] .Session.Id == 1）来自[ x]。属性选择[a] => GroupBy（[a] .AttributeDefinition.Id，[a]）}

不支持GroupBy上的SelectMany吗？还是我应该怎么写这个LINQ语句？

这是我要转换的SQL代码：

select s.*
  from (
    select max(a2.setpoint_id) as setpoint_id
    from
    SetPoints s2, 
    Attributes a2
    where
    a2.setpoint_id = s2.setpoint_id
    group by a2.attributedefinition_id
  ) as x
  inner join SetPoints s on x.setpoint_id = s.setpoint_id;

感谢您的帮助！