Custom views for cgridview based on role

I want to filter my CgridView to only display has "student" role from Authassignment Model, I read some tutorials but none of them show this. Please help me, this is related to my thesis.

<?php 

$this->widget('zii.widgets.grid.CGridView', array(
    'id'=>'users-grid',
    'dataProvider'=>$model->search(),
    // 'filter'=>$model,
    'columns'=>array(

        'userID',
        'lastname',

        array(
            'class'=>'bootstrap.widgets.TbButtonColumn',
        ),
    ),
)); 

?>

StudentView

I don't know what's your table structure is but the best way of doing this may be as follows. Create a field in user table named user_role and at the time of user creation insert value in this like 1 for admin 2 for student and then you can easily get only student role by below method:

public function actionIndex()
    {
        $model=new User('search');
                
        $model->unsetAttributes();  // clear any default values
        $model->user_role = 2;// for student role 
        if(isset($_GET['User']))
            $model->attributes=$_GET['User'];
 
        $this->render('index',array(
            'model'=>$model,
        ));
    }