Hi,

I created a new costom model product:

class costum_product(models.Model):
    _name = "costum.product"
    _inherit = "product.product"
    _description = "Costum Product Description" 
    name = fields.Char('Description', required= True) 
    code = fields.Integer('Code', required= True) 
    category_id = fields.Many2one('randa.category','Category')

And I tried to link it to sale module instead of the standard odoo product module:

class myModuleSaleOrderLine(models.Model):  
    _inherit = 'sale.order.line'  
    custom_product_id = fields.Many2one('costum.product', string='Product', ondelete='restrict', change_default=True, required=True)

 Now when I go to sales orders and add a sale order line, I can't add any line, whatever I do to save I got this warning:

The line has been modified, your changes will be discarded. Are you sure you want to discard the changes ?

And I can't add any line.