========================================
|| *id* | created | user_id | post_id ||
========================================

$userHasLikedThisPost = $this->Like->hasAny(array(
    'user_id' => $this->Auth->user('id'),
    'post_id' => $postId
));

public function hasLike($postId, $userId) {
    return $this->hasAny(array(
        'user_id' => $userId,
        'post_id' => $postId,
    ));
}