get invoice line items summary when doing Invoice.all with page request

Having "page" query on your Invoice single API call will return line items included on the response for each invoice

You can achieve getting the invoice line items by doing:

e.g 

      invoices = xero.Invoice.all(:page => 1)

Access the line items without forcing a download of an incomplete summary invoice like
     

     invoices.each do |invoice|
         invoice.line_items_summary
     end


see http://developer.xero.com/documentation/api/invoices/  under GET Invoices section.