如何在laravel中使用slug获取下一条和前一条记录

php artisan make:migration add_slug_to_posts_table --table=posts

public function up()
{
    Schema::table('posts', function (Blueprint $table) {
        $table->string('slug')->unique()->nullable();
    });
}

php artisan migrate

public function getRouteKeyName()
{
    return 'slug';
}

public function setSlugAttribute($value)
{
    $this->attributes['slug'] = Str::slug($value);
}

$nextPost = Post::where('slug', '>', $currentPost->slug)->orderBy('slug')->first();
$previousPost = Post::where('slug', '<', $currentPost->slug)->orderBy('slug', 'desc')->first();