How to fix the tree after adding nesting set through a migration?

[ludgerey]

I need to add the nested set columns to an existing table. Adding the nested set columns with a migration like below works as intended, but the tree is in a faulty state after that. parent_id is null, which is fine, as a hierarchy cannot be known at this point. But _lft and _rgt is all 0, so all subsequent nested set functions don't work.

Schema::table('units', function (Blueprint $table) {
	$table->nestedSet();
});

My first guess was to fix the tree using Unit::fixTree(). But this didn't do the trick. Also Unit::countErrors(); shows zero errors.

Expected behavior:

There should be some way to get the tree fixed. This means, that _lft and _rgt values have working values in some kind of order and the values should take into consideration an optional scope.

Getting the nested set fixed, after a migration should either be done by executing the migration using $table->nestedSet(); or by calling Unit::fixTree() or similar.

[ludgerey]

My additional workaround migration code using id as source value:

Without scoping:

\App\Unit::each(function (\App\Unit $unit) {
    $unit->setLft($unit->id * 2 - 1);
    $unit->setRgt($unit->id * 2);
    $unit->save();
});

With scoping:

\App\Unit::each(function (\App\Unit $unit) {
    $lowest = $unit->project->units->sortBy('id')->first()->id;

    $unit->setLft(($unit->id - $lowest + 1) * 2 - 1);
    $unit->setRgt(($unit->id - $lowest + 1) * 2);
    $unit->save();
});