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.