setting callback function within a model in config file

I have set the various validation rules for different pages in a config file. And in one page I want to check if a username exists or not. Is it possible to create a validation rule in the config file itself? but I created the function for checking in a model. I want to know if it is not possible to call the callback function in that model in config file?

I have read the article in http://codeigniter.com/wiki/MY_Validation_-_Callbacks_into_Models/. In that article it specified that we will have to be call the validation rule like:

$this->form_validation->run($this);

and by setting the valid开发者_如何学Goation rules in a config file, we will have to call the function like:

$this->form_validation->run('name of rule in config file');

How do I join both these?

setting a rule for validation by a callback is done just using a string. From that link:

$this->validation->set_rules(array(
        'username'    => 'trim|required|callback_users_model->is_unique[username]',
        'password'    => 'trim|required|matches[confirm]',
    )); 

you can see that the callback method is set using a string

callback_users_model->is_unique[username]

where you just use a string

$rule = 'callback_' . $model_class . '->' $function_name . '[username]';

now you can just load $model_class and $function_name from your config the same as usual:

$model_class = $this->config->item('validation.model.class');
$function_name = $this->config->item('validation.method');