How to join when using groupby - sql

Question

I have two tables of picturedetails and picture likes in mydatabase.
public partial class picturedetail
{
public int idpictures { get; set; }
public int iduser { get; set; }
public string picTitle { get; set; }
public string picFilename { get; set; }
public System.DateTime pictime { get; set; }
public int likes { get; set; }
public int nuditylevel { get; set; }
public int fakeslevel { get; set; }
}
public partial class picturelike
{
public int idpicturelike { get; set; }
public int idpictures { get; set; }
public int iduser { get; set; }
public System.DateTime iddatetime { get; set; }
public int iduserlikedby { get; set; }
public int likenumber { get; set; }
}
Its my Data Transfer Object (DTO) to avoid anonymous type error
public class LikesandPictureDetails
{
public int IdPicturess { get; set; }
public int IdUserPic { get; set; }
public string PicTitle { get; set; }
public string picFilename { get; set; }
public System.DateTime? PicTime { get; set; }
public int Likes { get; set; }
public int NudityLevel { get; set; }
public int FakesLevel { get; set; }
public int IdPicturelike { get; set; }
public int IdUser { get; set; }
public System.DateTime? IdDatetime { get; set; }
public int IduserLikedby { get; set; }
public int LikeNumber { get; set; }
public int IdPictures { get; set; }
public float totalrating { get; set; }
public int Count { get; set; }
}
I am successfully able to count the individual ratings of the picture and then divide by their counts. Now i want to show totalrating in my picture details table. How to achieve this thing? This is my code:
var query =
db.picturelikes.GroupBy(n => n.idpictures).Select(group =>
new LikesandPictureDetails
{
IdPictures = group.Key,
totalrating = (group.AsEnumerable().Sum(o => o.individualrating)) / group.Count(),
});
here likesandpicturedetails is acting as a dto.

Answer 1

Well, first of all you should use method Average to calculate average value. But in your case
But, as you need to calculate overall rating, why don't you calculate sum and average in the same step:
db.picturelikes.GroupBy(n => n.idpictures).Select(group =>
new LikesandPictureDetails
{
IdPictures = group.Key,
averageRating = (group.AsEnumerable().Average(o => o.individualrating)),
totalRating = (group.AsEnumerable().Sum(o => o.individualrating)),
});