from trytond.pool import PPoolMeta
from trytond.model import fields, Workflow
from trytond.transaction import Transaction


class Invoice(metaclass=PoolMeta):
    __name__ = 'account.invoice'

    @classmethod
    @ModelView.button
    @Workflow.transition('posted')
    def post(cls, invoices):
        for invoice in invoices:
            for line in invoice.lines:
                line.set_value()
        cls.save(invoices)
        super().post(invoices)


class InvoiceLine(metaclass=PoolMeta):
    __name__ = 'account.invoice.line'

    saved_value = field.Boolean("Saved Value", readonly=True)

    def set_value(self)
        self.saved_value = True