First,  thank you Serpent CS for upgrading jasper_reports to work with Odoo 8.

https://github.com/JayVora-SerpentCS/Jasperv8

It works nicely. Except 1 thing, on Sales Order form, it does not disply order lines. I found that despite we have declare, as example, OPENERP_RELATIONS = ["order_line"], as we want to loop through Sales Order's Lines. It still display only the 1st line.

After dig through code, I found the problem in /jasper_reports/JasperReports/BrowseDataGenerator.py -> in the method def generateIds(.....)

Following part of code think "order_line" is not a list (in v8 order_line is recordset), and so it just give log warning and ignore it. 

                if not isinstance(value, list):

                    self.warning("Field '%s' in model '%s' is not a relation." % (root, self.model))

                    return currentRecords

My solution is just comment this part out. And now it works !!!