How to get list of results in Linq - linq

Question

I'm taking a list of counts, averaging and returning all results according to the condition. Looks like my command is too erroneous. I don't know how to do it yet.
I have tables:
var qr = (from Product c in _context.Products
join o in _context.RatingProducts on c.ID equals o.IDProduct
where c.Status == true
orderby c.NumProduct
group o by c.ID into g
select new {
ProductId = g.Key,
CountID = g.Count(),
//SumID = g.Sum(s => s.StarRating).ToString(),
AveragedID = g.Count() > 0 ? g.Average(x => x.StarRating) : 0
}).ToList();
var getqr = _context.Products.Where(a => a.Status).ToList();
int count = 0;
double averaged = 0;
foreach (var item in getqr)
{
int key = item.ID;
var id = qr.Where(x => x.ProductId == key).FirstOrDefault();
if(id != null)
{
count = id.CountID;
averaged = Math.Round(id.AveragedID,1);
}
var productquery = item;
}
var query = from c in qr
join p in getqr on c.ProductId equals p.ID
select new ProductQuery
{
ID = p.ID,
IDProduct = p.IDProduct,
CategoryID = p.CategoryID,
NumProduct = p.NumProduct,
Name = p.Name,
Status = p.Status,
Price = p.Price,
PriceOld = p.PriceOld,
ContentsSmall = p.ContentsSmall,
Contents = p.Contents,
Images = p.Images,
CountID = count,
//SumID = c.SumID,
AveragedID = averaged,
};
return query.ToList();
However when I debug, it shows only one result with row ID = 1. I want to display list: count, average results of table 1. Tks.

Answer 1

As far as I understand you should make LEFT JOIN here, so need to add DefaultIfEmpty in the initial query, and slightly change average counting logic.
Something like this, should work:
var qr = (from Product c in _context.Products
join o in _context.RatingProducts on c.ID equals o.IDProduct into productRatings
from pr in productRatings.DefaultIfEmpty()
where c.Status == true
orderby c.NumProduct
group o by c.ID into g
select new {
ProductId = g.Key,
CountID = g.Count(),
AveragedID = g.Average(x => x == null ? 0 : x.StarRating)
}).ToList();