C# 在linqtosql中，我可以在groupby中有一个select（和groupby）吗？

我有以下课程：

class XXX
{
    int XXXType{get;set;}
    List<YYY> Children{get;set;}
}
class YYY
{
    int YYYType{get;set;}
}

像这样的

//样本数据

   var xxxList = new List<XXX> {
            new XXX()
            {
                XXXType = 1,
                Children = new List<YYY>() {
                        new YYY() {YYYType = 1},
                        new YYY() {YYYType = 1},
                        new YYY() {YYYType = 2},
                        new YYY() {YYYType = 2}
                    }
            }
        };

结果: XXX类型：1，XXX类型数：1，子类型数：2

   var xxxList = new List<XXX> {
            new XXX()
            {
                XXXType = 1,
                Children = new List<YYY>() {
                        new YYY() {YYYType = 1},
                        new YYY() {YYYType = 1},
                        new YYY() {YYYType = 2},
                        new YYY() {YYYType = 2}
                    }
            }
        };

        foreach(var x in xxxList.GroupBy(info => info.XXXType)
                    .Select(group => new { 
                         key = group.Key, 
                         Count = group.Count(),
                         YYYChildren = (from y in xxxList.SelectMany(z=>z.Children).GroupBy(y=>y.YYYType, (key, values) =>
                                        new {
                                             YYYType = key,
                                             Count = values.Count()
                                        }) select y.YYYType)
                    }))
        {
             Console.WriteLine("XXXType :{0}, Number Of XXXTypes :{1}, Number Of YYYChildren :{2}", x.key, x.Count, x.YYYChildren.Count());
        }