嵌套GroupBy查询mongo驱动程序

Question

  

我正在尝试创建嵌套对象，但出现此错误：

     

表达式树中不支持GroupBy方法：   {document} .GroupBy（y => y.Select（z => z.DamageId））。

     

请帮助如何使查询工作？

    var a = await UsersDataDB.HappendToMe
        .AsQueryable()
        .Select(x => x.MedDamages)
        .GroupBy(x => x.Select(x => x.ProductId))              
        .Select(x => new
        {
            MedicineId = x.Key,
            Damages = x.GroupBy(y => y.Select(z => z.DamageId))
                                      .Select(c => new
                                      {
                                          DamageId = c.Key,
                                          DamageType = c.GroupBy(d => d.Select(d => d.Damgetype))
                                                                      .Select(e => new
                                                                      {
                                                                          Damgetype = e.Key,
                                                                          HappendType = e.GroupBy(f => f.Select(f => f.HappendType))
                                                                                                       .Select(g => new
                                                                                                       {
                                                                                                           HappendType = g.Key,
                                                                                                           HappendCount = g.Count()
                                                                                                       })
                                                                      })
                                      })
        }).ToListAsync();

  public IMongoCollection<HappendToMe> HappendToMe
    {
        get
        {
            return db.GetCollection<HappendToMe>("HappendToMe");
        }
    }

public class HappendToMe
{
    [BsonId]
    public ObjectId UserId { get; set; }

    public List<Damage> MedDamages { get; set; }
}

public class Damage
{
    public ObjectId ProductId { get; set; }
    public ObjectId DamageId { get; set; } 
    public byte Damgetype { get; set; } 
    public byte HappendType { get; set; }
}