CakePHP: Select DISTINCT in ContainableBehaviour

I am trying to select only distinct related model entries but it seems it doesn't work.

I have this:

$active_questions = $this->Question->find('all', array('conditions' => array('test_id' => $active_tests), 'fields' => array('answer_style_id'), 'contain' =>开发者_开发知识库 array(
        'Answer' => array(
            'fields' => array('capital_category_id'),
            'CapitalCategory' => array(
                'fields' => array('id', 'DISTINCT capital_id', 'DISTINCT category_id', 'delete_flag'),
                'Capital' => array(
                    'fields' => array('id', 'delete_flag')
                ),
                'Category' => array(
                    'fields' => array('id', 'delete_flag')
                )
            )
        )
    )));

But Cake seems to automatically add the associated model key, even id I specified it with a DISTINCT keyword:

Query: SELECT `CapitalCategory`.`id`, DISTINCT `CapitalCategory`.`capital_id`, DISTINCT `CapitalCategory`.`category_id`, `CapitalCategory`.`delete_flag`, `CapitalCategory`.`capital_id`, `CapitalCategory`.`category_id` FROM `capital_categories` AS `CapitalCategory`   WHERE `CapitalCategory`.`id` = 217  

How do I filter out only DISTINCT capitals or categories? For the current example, Cake returns 20 categories with the same id. I want only one to be returned.

Thank you.

Off the top of my head, the following may work using the 'group' option

$active_questions = $this->Question->find(
  'all', 
  array(
    'conditions' => array('Question.test_id' => $active_tests), 
    'fields' => array('answer_style_id'), 
    'contain' => array(
      'Answer' => array(
        'fields' => array('capital_category_id'),
        'CapitalCategory' => array(
          'fields' => array('id', 'capital_id', 'category_id', 'delete_flag'),
          'group' => array('capital_id', 'category_id'),
          'Capital' => array(
            'fields' => array('id', 'delete_flag')
          ),
          'Category' => array(
            'fields' => array('id', 'delete_flag')
          )
        )
      )
    )
  )
);

Why don't you put 'group' just below 'fields' and not inside 'contain', also you may have to remove 'fields' altogether.