How insert null on save in select field

In your model, create the following method:

PHP Code:

protected function setDefaultIDMezzi(array $data) {
    if(!isset($data['data']['id_mezzi']))
        $data['data']['id_mezzi'] = NULL;
    return $data;
} 


You must then configure your model to call this method before each insert (and update if desired) by including these protected variables:

PHP Code:

protected $beforeInsert = ['setDefaultIDMezzi'];
protected $beforeUpdate = ['setDefaultIDMezzi']; 


Please review the documentation to make sure you completely understand: https://codeigniter.com/user_guide/model...your-model.