Validate form without model

Hi, i have a controller is name is Hirdetes.

public function actionCreate()

	{

                $model=new Kategoriak;

                

                if(isset($_POST['Kategoriak']) && !empty($_POST['Kategoriak']['kategoria'])) {

                    $_SESSION['kategoria'] = $_POST['Kategoriak']['kategoria'];

                    $this->redirect(array(Yii::app()->baseUrl.'/user/registration'));

                }

		$this->render('create',array(

			'model'=>$model,

		));

	}

My create form:

<?php

$this->breadcrumbs=array(

	'Hirdetes Feladas'=>array('/hirdetesFeladas'),

	'Create',

);?>

<h1><?php echo $this->id . '/' . $this->action->id; ?></h1>


<div class="form">

<?php $form=$this->beginWidget('CActiveForm', array(

	'id'=>'hirdezes-feladas-form',

	'enableAjaxValidation'=>true,

        'enableClientValidation'=>true

)); ?>

        <?php echo $form->errorSummary($model); ?>

        <?php if(isset($_SESSION['kategoria'])) echo $_SESSION['kategoria']; ?>

        

        <?php 

            $fa=  Kategoriak::model()->findAll();

            $valasz = CHtml::listData($fa,'id','kategoria');

            $prompt = array('prompt'=>Yii::t('layout','Please select')); 

        ?>

    

        <?php // var_dump($model); exit; ?>

	<div class="row">

		<?php echo $form->labelEx($model,'kategoria'); ?>

                <?php echo $form->dropDownList($model,'kategoria', $valasz, $prompt); ?>

		<?php echo $form->error($model,'kategoria'); ?>

	</div>


	<div class="row buttons">

		<?php echo CHtml::submitButton($model->isNewRecord ? 'Tovább' : 'Save'); ?>

	</div>


<?php $this->endWidget(); ?>

</div>

How to validate this form? The criteria is, the kategoria is not empty.

When i use this:

if(isset($_POST['Kategoriak']) && !empty($_POST['Kategoriak']['kategoria']) && $model->validate('kategoria')) {

Show error, but when i selected a item.

It works.

                if(isset($_POST['Kategoriak'])) {

                    $model->attributes = $_POST['Kategoriak'];

                    if($model->validate(array('kategoria'))) {

                        $_SESSION['kategoria'] = $_POST['Kategoriak']['kategoria'];

                        $this->redirect(array(Yii::app()->baseUrl.'/user/registration'));

                    }

                }

		$this->render('create',array(

			'model'=>$model,

		));