>>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)};

>

Ok, this compiles:

var invoicesList = from invoices in _dbSet.Where(x => x.Account == accountName && x.Hidden == false)
                               let balance = (from transact in _siriusContext.Transact where transact.InvoiceNo == invoices.InvoiceNo
                                                  select transact).Sum(c=>c.Extension)
                                select new InvoicesList
                                {
                                    InvoiceNo = invoices.InvoiceNo,
                                    Account = invoices.Account,
                                    Hidden = invoices.Hidden,
                                    Descrip = invoices.Descrip1,
                                    Created = invoices.DateTime,
                                    Finalized = invoices.Finalized,
                                    Balance = (decimal?)balance??0
                                };

I'll try testing it now.