PostResource.php

<?php

use Laravel\Nova\Fields\ID;
use Laravel\Nova\Fields\Text;

/**
 * Get the fields displayed by the resource.
 *
 * @param  \Illuminate\Http\Request  $request
 * @return array
 */
public function fields(Request $request)
{
    return [
        ID::make()->sortable(),
        Text::make('Title')->sortable(),
        Textarea::make('Description'),
        Date::make('Created At'),
        Boolean::make('Active'),
        Select::make('Topic')->options([
            'S' => 'Shopping',
            'M' => 'Money',
            'L' => 'Lifestyle',
        ])->displayUsingLabels(),
    ];
}