How do I sync many to many records with multiple models using an action in Laravel Nova?

Just like you wrote it. Use sync or toggle or who knows what new methods Laravel has for that use case.

Hey, thank you.. I guess I need a little more help than that. Is there docs anywhere on doing that? I understand how to with single items, but the main thing I am looking for is doing it with multiple items.. Through an action.

Check this out https://laravel.com/docs/7.x/eloquent-relationships#updating-many-to-many-relationships

$user->roles()->sync([1, 2, 3]);

$user->roles()->syncWithoutDetaching([1, 2, 3]);

$user->roles()->toggle([1, 2, 3]);

I think this will only confuse you, but in Nova that would look something like

public function handle(ActionFields $fields, Collection $models)
{
    // only allow this action on details page (new ActionName)->onlyOnDetail()
    // cause I assume that you do not want same relationships to be applied
    // all your models
    $models->first()->roles()->sync(
        collect(array_filter($fields->getAttributes(), 'is_int'))->values()
    );
}

public function fields(): array
{
    // this bit is ugly since you want to use it through actions
    // so you have to fetch resource ID somehow
    $resourceId = request()->get('resourceId') ?? request()->get('resources');
    if (!$resourceId) {
        return [];
    }
    $model = Model::query()->find($resourceId);

    return $model->roles()
        ->pluck('text', 'id')
        ->map(function (string $text, int $id) use ($model): Element {
            return Boolean::make($id, 'role_'.$id)
                ->help(ucfirst($text))
                ->values($id, false)
                ->withMeta(['value' => collect($model->roles)->contains($id)]);
        })
        ->prepend(Heading::make('Select those that apply')) // this is only to style things better
        ->toArray();
}

Thank you! I think that is what I am looking for.

You can use this package https://github.com/dillingham/nova-attach-many