from trytond.pool import PoolMeta
from trytond.model import fields
from trytond.pyson import Eval


class Sale(metaclass=PoolMeta):
    __name__ = 'sale.sale'

    delete_lines = fields.One2Many(
        'sale.line',
        'sale',
        "Delete lines",
        states={
            'readonly': Eval('state') != 'draft'
        }
    )