Hi,

As the  res_partner_id field is the inverse relation(many2one) from the one2many model to main model, you have to set corresponding value in the res_partner_id during the creation and see.

data_attach = {
    'name': fileo['Name'],
    'type': 'url',
    'url': url1,
    'datas_fname': fileo['Name'],
    'res_model': 'res.partner',
    'res_id': self.id,
    'res_partner_id': value,
}

Thanks