Expressive Syncing in Laravel
sync accepts a second parameter that prevents a model from detaching any associations.
$post->tags()->pluck('id'); // 1, 3, 5
$post->tags()->sync([2, 4], false);
$past->tags()->pluck('id'); // 1, 2, 3, 4, 5If you haven't check the Laravel docs lately there's a nice, new syncWithoutDetaching method that makes your code a whole lot more expressive.
$post->tags()->pluck('id'); // 1, 3, 5
$post->tags()->syncWithoutDetaching([2, 4]);
$past->tags()->pluck('id'); // 1, 2, 3, 4, 5