Dependant select2 with ajax

[pxpm]

          Good afternoon @tabacitu ,

How do I use this same structure in Backpack 6.x? I have a table of States and another of Cities and I need the city combo to depend on the state information.

On Controller:

[
     'name' => 'state_id',
     'label' => 'Estado',
    'type' => 'select2',
    'entity' => 'state', // the method that defines the relationship in your Model
    'model' => "App\Models\State", // foreign key model
    'attribute' => 'uf_name', // foreign key attribute that is shown to user
    'allows_null' => true,
    'placeholder' => "Selecione o Estado",
    'options' => (function ($query) {
          return $query->orderBy('uf', 'ASC')->get();
    }),
],
[ // select2_from_ajax: 1-n relationship
    'name' => 'city_id',
    'label' => 'Município', // Table column heading
    'type' => 'select2_from_ajax',
    'ajax' => false,
    'model' => "App\Models\City", // foreign key model
    'entity' => 'city', // the method that defines the relationship in your Model
    'attribute' => 'name', // foreign key attribute that is shown to user
    'data_source' => url('api/city'), // url to controller search function (with /{id} should return model)
    'method' => 'GET', // route method, either GET or POST
    'allows_null' => true,
    'placeholder' => 'Selecione o município', // placeholder for the select
    'minimum_input_length' => 0, // minimum characters to type before querying results
    'dependencies' => ['state_id'],
],

On City Api:

    public function index(Request $request)
    {
        $search_term = $request->input('q');
        $form = collect($request->input('form'))->pluck('value', 'name');

        $options = City::query();

        // if no category has been selected, show no options
        if (!$form['state_id']) {
            return [];
        }

        // if a category has been selected, only show articles in that category
        if ($form['state_id']) {
            $options = $options->where('state_id', $form['state_id']);
        }

        if ($search_term) {
            return $options->where('name', 'ilike', '%' . strtoupper($search_term) . '%')
                ->orderBy('name')
                ->paginate(10);
        }

        return $options->paginate(10);
    }
    public function show($id)
    {
        return City::find($id);
    }

Return Error: Undefined array key "state_id"

Could you help me with this problem or give me a cool alternative?

Originally posted by @helesjunior in https://github.com/Laravel-Backpack/CRUD/issues/1484#issuecomment-2148305097