<?php

class Works
{
	private static $worksTree = null;

	public static function getWorksTree($force = false)
	{
		if (self::worksTree === null || $force) {
			self::worksTree = [];
			
			$sql = "SELECT c.id AS categoryId,
						   c.title AS categoryTite,
						   t.id AS categoryTypeId ,
						   t.title AS categoryTypeTitle,
						   w.id AS workId,
						   w.title AS workTitle
					FROM works w
					INNER JOIN categories c ON c.id = w.categoryId
					INNER JOIN categoryTypes t ON t.id = c.categoryTypeId";
					
			$worksTree = DI::db->findBySql($sql)->all();
			
			foreach ($worksTree as $tree) {
				self::worksTree[$tree['categoryId']]['title'] = $tree['categoryTite'];
				self::worksTree[$tree['categoryId']]['types'][$tree['categoryTypeId']]['title'] = $tree['categoryTypeTitle'];
				self::worksTree[$tree['categoryId']]['types'][$tree['categoryTypeId']]['works'] = [
						'id' => $tree['workId'],
						'title' => $tree['workTitle']
				];
			}
		}
		
		return self::$worksTree;
	}
}


print_r(Works::getWorksTree());
//должно получится что-то вроде этого
//Array()
//[1] => Array()
//		['title'] => 'Category One'
//		['types'] => Array()
//                      [1] => Array()
//				['title'] => 'Type One'
//				['works'] => Array()
//						[0] => Array()
//							['id'] => 1
//							['title'] => 'Work One'
//						[1] ...
//		          [2] ....
//[2] ...