Tree structure in Dropdown using Yii

In this tutorial, we create tree structure dropdown list like as below :-

RHCE
--SE1
RHCSA
--SA1
--SA2
PHP

Table strucure for this kind of tree is as below :
id parent_id course_name
1     0               RHCE
2     0               RHCSA
3     1               SE1
4     2               SA1
5     2              SA2
6     0              PHP

I have create class file in component folder because i can use it anywhere in my application but you can create this file's function anywhere.

In components folder create a new class CommonMethods.

<?php
/*
* /protected/components/CommonMethods.php

 */
class CommonMethods {
 
    private $data = array();
   
    public function makeDropDown($parents)
    {
        global $data;
        $data = array();
        $data['0'] = '-- ROOT --';
        foreach($parents as $parent)
        {
           
                $data[$parent->id] = $parent->name;
                $this->subDropDown($parent->children);
               
        }
       
       return $data;
    }
   
  public function subDropDown($children,$space = '---')
    {
        global $data;
       
        foreach($children as $child)
                {
                   
                        $data[$child->id] = $space.$child->name;
                        $this->subDropDown($child->children,$space.'---');
                }
       
    }
   
   
}
?>

In you model make relations.
public function relations()
{
                  return array(

                    'parent' => array(self::BELONGS_TO, 'CourseMaster', 'parent_id', 'condition' => 't.parent_id <> 0'),

                    'children' => array(self::HAS_MANY, 'CourseMaster', 'parent_id'),

               );

}

In your view _form.php
    <div class="row">

       <?php


          $parents = CourseMaster::model()->findAll('parent_id = 0');
 $cm = new CommonMethods();

          $data = $cm->makeDropDown($parents);


          echo $form->labelEx($model,'parent_id');

          echo $form->dropDownList($model,'parent_id',  $data);


      ?>


    </div>