整体形式：

class Form implements RecursiveIterator{
    private $id;
    private $caption;
    private $other_text;
    private $questions = array();
    private $current;
 
    private function __construct(DibiRow $row){
        $this->id = $row->id;
        $this->caption = $row->caption;
        $this->other_text = $row->other_text;
        $this->loadQuestions();
    }
 
    private function loadQuestions(){
        $questions = dibi::query('SELECT * FROM cyp_questions WHERE form_id = %i AND parent_id IS NULL',$this->id);
        while($question = $questions->fetch()) $this->questions[] = new Question($question->question_id,$question->type,$question->caption,$question->other_text,$question->triggers_unique == 1);
    }
 
    /**
     * @throws InvalidArgumentException
     * @param $id
     * @return Form
     */
    public static function loadById($id){
        $form = dibi::query('SELECT * FROM cyp_forms WHERE id = %i',$id)->fetch();
        if($form === false) throw new InvalidArgumentException('Form with id '.$id.' was not found.');
 
        return new Form($form);
    }
 
    /**
     * @throws FormFieldException
     * @return bool
     */
    public function validate($postfields){
 
    }
 
    public function getQuestions(){
        return $this->questions;
    }
 
    public function getChildren(){
        return $this->questions[$this->current];
    }
 
    public function hasChildren(){
        return count($this->questions) > 0;
    }
 
    public function current(){
        return $this->questions[$this->current];
    }
 
    public function key(){
        return $this->current;
    }
 
    public function next(){
        $this->current++;
    }
 
    public function rewind(){
        $this->current = 0;
    }
 
    public function valid(){
        return isset($this->questions[$this->current]);
    }
}

题：

class Question implements RecursiveIterator{
    private $id;
    private $type;
    private $answers = array();
    private $subquestions = array();
    private $other_text;
    private $triggers_unique;
    private $caption;
    private $current = 0;
 
 
    public function __construct($id,$type,$caption,$other_text = null,$triggers_unique = false){
        $this->id = $id;
        $this->type = $type;
        $this->caption = $caption;
        $this->other_text = $other_text;
        $this->triggers_unique = $triggers_unique;  
        $this->setSubQuestions();   
 
    }
 
    private function setSubQuestions(){
        $questions = dibi::query('SELECT * FROM cyp_questions WHERE parent_id = %i',$this->id);
        while($question = $questions->fetch()) $this->subquestions[] = new Question($question->question_id,$question->triggers_unique == 1);
    }
 
    public function getOtherText(){
        return $this->other_text;
    }
 
    public function getCaption(){
        return $this->caption;
    }
 
    public function addAnswer($answer){
        $this->answers[] = $answer;
    }
 
    public function getChildren(){
        return $this->subquestions[$this->current];
    }
 
    public function hasChildren(){
        return count($this->subquestions) > 0;
    }
 
    public function current(){
        return $this->subquestions[$this->current];
    }
 
    public function key(){
        return $this->id;
    }
 
    public function next(){
        ++$this->current;
    }
 
    public function rewind(){
        $this->current = 0; 
    }
 
    public function valid(){
        return isset($this->subquestions[$this->current]);
    }
 
    public function getAnswers(){
        return $this->answers;
    }
 
 
}

迭代：

$form = Form::loadById(1);
 
foreach($form as $question){
    echo $question->getCaption().'<br />';  
}