Hi,

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) > 15:

raise ValidationError('Not more than 15lines')

When a user attempts to add more than 15 lines to a sale order, the constraint will be triggered and prevent the change from being saved.

Hope it helps