first implementation draft

from trytond.pool import Pool

from . import subscription

__all__ = ['register']

def register():

    Pool.register(

        subscription.Subscription,

        module='subscription_include', type_='model')

    Pool.register(

        module='subscription_include', type_='wizard')

from trytond.model import ModelView, fields

from trytond.pool import PoolMeta

from trytond.pyson import Eval

__all__ = ['Subscription']

class Subscription(metaclass=PoolMeta):

    "Subscription"

    __name__ = 'sale.subscription'

    include = fields.Boolean("Include", states={'readonly': Eval('state') != 'draft'})

    def compute_next_invoice_date(self):

        date = super(Subscription, self).compute_next_invoice_date()

        if(self.include and not self.next_invoice_date):

            return self.invoice_start_date or self.start_date

        else:

            return date

 No newline at end of file

<?xml version="1.0"?>

<tryton>

    <data>

        <record model="ir.ui.view" id="subscription_view_form">

            <field name="model">sale.subscription</field>

            <field name="inherit" ref="sale_subscription.subscription_view_form"/>

            <field name="name">subscription_form</field>

        </record>

    </data>

</tryton>

 No newline at end of file

[tryton]

version=4.8

version=4.8.0

depends:

    account

    account_invoice

    company

    currency

    ir

    product

    res

    sale

    sale_subscription

xml:

    subscription.xml

<?xml version="1.0"?>

<data>

    <xpath expr="/form/notebook/page[@id='subscription']/field[@name='start_date']" position="after">

        <label name="include"/>

        <field name="include" xexpand="0" width="25"/>

    </xpath>

</data>

 No newline at end of file