C# 在linq中使用groupby时如何进行多个联接

我的数据库中有一张图表。对于每个新的评级，将创建一个新的图片评级表行。我将这些评级按上周和pictureid进行分组，这意味着上周一张图片的所有评级都将被累加并成为一个评级。然后我将能够按它们的计数对它们进行排序

这是我的桌子：

public partial class picturerating
{
     public int idpicturerating { get; set; }
     public int idpictures { get; set; }
     public int iduser { get; set; }
     public System.DateTime iddatetime { get; set; }
     public int iduserratedby { get; set; }
     public int rating { get; set; }
}

这是我执行此操作的代码：

      public IQueryable<SortedDto> GetRatignsAndTheirDetails()
    {
        var pastDate = DateTime.Now.Date.AddDays(-7);
        var combo = from p in db.picturerating
                    where p.iddatetime > pastDate
                    group p by p.idpictures into pgroup
                    let count = pgroup.Count()
                    orderby count descending
                    select new SortedDto
                    {
                        IdPictures = pgroup.FirstOrDefault().idpictures,
                        IdPicturerating = pgroup.FirstOrDefault().idpicturerating,
                        IdUser = pgroup.FirstOrDefault().iduser,
                        IdDatetime = pgroup.FirstOrDefault().iddatetime,
                        IdUserratedBy = pgroup.FirstOrDefault().iduserratedby,


                    };

        return combo;
    }

---

我做得对吗？方法是什么？如何更改上面的代码，使其根据我的需要正常工作

那么什么不能正常工作呢？第三个代码中的连接，我写它们只是为了给你一个想法，这是我应该连接的方式吗？

 var pastDate = DateTime.Now.Date.AddDays(-1);
        var combo = from p in db.picturedetails
                    join u in db.users on p.iduser equals u.iduser
                    join l in db.pictureratings  where l.iddatetime > pastDate group l by l.idpictures into pgroup
                    let count = pgroup.Count()
                    orderby count descending

                    select new SortedDto
                    {
                        IdPictures = pgroup.FirstOrDefault().idpictures,
                        IdPictureRating = pgroup.FirstOrDefault().idpicturerating,
                        IdUser = pgroup.FirstOrDefault().iduser,
                        IdDatetime = pgroup.FirstOrDefault().iddatetime,
                        IdUserRatedBy = pgroup.FirstOrDefault().iduserrateddby,
                        username=u.username,
                        dob=u.dob,
                        sex=u.sex,
                        totalrating = pl.Average(l => (float?)l.rating)?? 0 , // pl.Where(a => a.ratenumber!= null).Average(c => c.ratenumber)

                    };

        return combo;