Tool.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use LaravelFillableRelations\Eloquent\Concerns\HasFillableRelations;


class Tool extends Model
{
    use HasFillableRelations;

    protected $fillable = ['name'];
    protected $fillable_relations = ['fields'];

    public function fields()
    {
        return $this->hasMany(static::class . 'Field');
    }
}

class ToolField extends Model
{
    use HasFillableRelations;

    protected $fillable = ['name'];
    protected $fillable_relations = ['choices'];

    public function choices()
    {
        return $this->hasMany(static::class . 'Choice');
    }
}

class ToolFieldChoice extends Model
{
    protected $fillable = ['name'];
}