how to group by parent and apply aggregate function on its childeren in LinQ Lambda

Question

I have a SQL table which holds a parent-child relationship in it own schema via a ParentId column. There are some other tables (Sale, etc.) linked to it via the LocationId column. I am after grouping data based on the second level parents (Code: xxxxx.xxxxx) and then apply some aggregate function such as SUM and COUNT to its children and itself .

Expectation Result for seeing the total sales for 2 regions(Victoria, South Australia) would be something like:

DisplayName      TotalSale
Victoria         $25,000
South Australia  $30,000

Answer 1

I managed to solve the above situation through the Code column on the table:

var t = await _jobRepository.GetAll().Include(p => p.Applications)
                                           .Include(p => p.Location)
                                           .Include(p => p.InvoiceItem)
                                           .Where(p => p.PublishDate.HasValue)
                                           .Where(p => p.PublishDate.HasValue)
                                           .Where(p => p.PublishDate.Value.Year == Clock.Now.Year && p.PublishDate.Value.Month == Clock.Now.Month)
                                           .Where(p => p.Location.Code.Length >= 11)
                                           .GroupBy(p => p.Location.Code.Substring(0, 11), p => p, (parentLocation, job) => new { parentLocation, job })
                                           .Select(p => new RegionalStatCountryToBeChanged()
                                           {
                                               RegionName = p.job.Select(q => q.Location).FirstOrDefault(q => q.Code == p.parentLocation).DisplayName,
                                               NumberOfAds = p.job.Count(),
                                               NumberOfApplications = p.job.SelectMany(q => q.Applications).Count(),
                                               Sales = p.job.Select(q => q.InvoiceItem).Sum(q => q.Price)
                                           })
                                           .ToListAsync();