$this->Project->contain();
$this->Project->virtualFields['completion'] = '
	ROUND(
		((SUM(Todo.complete) + SUM(TodoExtra.complete)) / 
		(COUNT(Todo.complete) + COUNT(TodoExtra.complete))) *
		100
	)
';
$projects = $this->Project->find('all', array(
	'joins' => array(
		array(
			'alias' => 'Todo',
			'table' => 'project_todos',
			'type' => 'LEFT',
			'conditions' => array(
				'`Todo`.`project_id` = `Project`.`id`',
			),
		),
		array(
			'alias' => 'TodoExtra',
			'table' => 'project_todo_extras',
			'type' => 'LEFT',
			'conditions' => array(
				'`TodoExtra`.`project_id` = `Project`.`id`',
			),
		)
	),
	'group' => array(
		'Project.id',
	),
));