Need Help For Complex Has_Many Relation Criteria

Hi
How can I return the newest Post of the specific Author in Yii Blog Demo ??
in the User model we have

	/**
	 * @return array relational rules.
	 */
	public function relations()
	{
		// NOTE: you may need to adjust the relation name and the related
		// class name for the relations automatically generated below.
		return array(
			'posts' => array(self::HAS_MANY, 'Post', 'author_id'),
		);
	}

I dont want Hard coded m I just need a simple way because I need to access newest record many times
thanks a lot