class SaleLine(metaclass=PoolMeta):
    __name__ = 'sale.line'

    number = fields.Function(fields.Char('Number'),
        'get_sale_field', searcher='search_sale_field')
    party = fields.Function(fields.Many2One('party.party', 'Sale Party'),
        'get_sale_field', searcher='search_sale_field')
    shipment_party = fields.Function(fields.Many2One('party.party',
            'Sale Shipment Party'), 'get_sale_field',
        searcher='search_sale_field')
    sale_date = fields.Function(fields.Date('Sale Date'), 'get_sale_field',
        searcher='search_sale_field')
    currency = fields.Function(fields.Many2One('currency.currency',
        'Currency'), 'get_sale_field', searcher='search_sale_field')
    invoice_product = fields.Many2One('product.product', "Invoice Product",
        ondelete='RESTRICT',
        domain=[
            If(Eval('sale_state').in_(['draft', 'quotation']),
                ('salable', '=', True),
                ()),
            ],
        states={
            'invisible': Eval('type') != 'line',
            'readonly': Eval('sale_state') != 'draft',
            },
        depends=['type', 'sale_state'],
        help="The product that should be invoiced.")
    invoice_product_customer = fields.Many2One(
        'sale.product_customer', "Invoice Customer's Product",
        ondelete='RESTRICT',
        domain=[
            If(Bool(Eval('invoice_product')),
                ['OR',
                    [
                        ('template.products', '=', Eval('invoice_product')),
                        ('product', '=', None),
                        ],
                    ('product', '=', Eval('invoice_product')),
                    ],
                []),
            ('party', '=', Eval('_parent_sale', {}).get('party')),
            ],
        states={
            'invisible': Eval('type') != 'line',
            'readonly': Eval('sale_state') != 'draft',
            },
        depends=['invoice_product', 'type', 'sale_state'])

    @classmethod
    def __setup__(cls):
        super().__setup__()
        cls.product_customer.states['invisible'] = Or(
            cls.product_customer.states.get('invisible', False),
            Eval('invoice_product_customer', False))
        cls.product_customer.depends.append('invoice_product_customer')

    def get_sale_field(self, name):
        field = getattr(self.__class__, name)
        value = getattr(self.sale, name)
        if value and isinstance(value, ModelSQL):
            if field._type == 'reference':
                return str(value)
            return value.id
        return value

    @classmethod
    def search_sale_field(cls, name, clause):
        return [('sale.' + name,) + tuple(clause[1:])]

    def _order_sale_field(name):
        def order_field(tables):
            pool = Pool()
            Sale = pool.get('sale.sale')
            field = Sale._fields[name]
            table, _ = tables[None]
            sale_tables = tables.get('sale')
            if sale_tables is None:
                sale = Sale.__table__()
                sale_tables = {
                    None: (sale, sale.id == table.sale),
                    }
                tables['sale'] = sale_tables
            return field.convert_order(name, sale_tables, Sale)
        return staticmethod(order_field)
    order_party = _order_sale_field('party')
    order_shipment_party = _order_sale_field('shipment_party')
    order_sale_date = _order_sale_field('sale_date')
    order_shipping_date = _order_sale_field('shipping_date')
    order_number = _order_sale_field('number')
    order_currency = _order_sale_field('currency')
    order_sale_state = _order_sale_field('state')