5.1.0

Added a second argument to save() to save external relations automatically. For example:

$post = $db->posts[5];

$post->tags = [1, 2, 5];
$post->comments = [3, 4];
$post->save(false, true); 

$tag = $db->tags[2];
$comment = $db->comments[3];

$tag->post_tags->post_id; // [5]
$comment->post_id; //5