>I got as far as
>
>

> var invoicesList = (from invoices in _dbSet.Where(x => x.Account == accountName && x.Hidden == false)
>                                join transact in _siriusContext.Transact on invoices.InvoiceNo equals transact.InvoiceNo into InvoiceBalance
>                                from rt in InvoiceBalance.DefaultIfEmpty()
>                                select new InvoicesList
>                                {
>                                    InvoiceNo = invoices.InvoiceNo,
>                                    Account = invoices.Account,
>                                    Hidden = invoices.Hidden,
>                                    Descrip = invoices.Descrip1,
>                                    Created = invoices.DateTime,
>                                    Finalized = invoices.Finalized,
>                                    Balance = (decimal?)rt.Extension??0
>                                });

>
>but this is still not what I want as I want sum of extension. Still struggling.

      var l = from inv in invoice
                        join ib in invoiceBalance on inv.id equals ib.id
                        group ib by inv.id into g
                        select new {InvoiceId = g.Key, Balance = g.Sum(s=>s.balance)};