Hi,

Here is a more simpler method,

Use @api.constrains to limit the adding of item in a one2many field

Here is sample code:

class SaleOrder(models.Model):
    _name = 'sale.order'
    _description = 'Sale Order'

    name = fields.Char(string='Name')
    sale_lines = fields.One2many('sale.order.line', 'order_id', string='Sale Lines')

    @api.constrains('sale_lines')
    def _check_sale_lines(self):
        for record in self:
            if len(record.sale_lines) > 20:
                raise ValidationError('Not more than 20 lines')

When a user attempts to add more than 20 lines to a sale order, the constraint will be triggered and prevent the change from being saved.

Regards

Hello,

you can use limit in one2many field. like this:

'order_line': fields.one2many('sale.order.line', 'order_id', 'Order Lines', limit=10),