ospro-api-laravel/app/Models/Divisi.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Divisi extends Model
{
    protected $table = 'm_divisi', $guarded = ['id'];
    protected $with = ['parent', 'children'];
    protected $casts = [
        'id' => 'integer',
        'parent' => 'integer'
    ];
    const CREATED_AT = 'created_at';
    const UPDATED_AT = 'updated_at';

    public static function boot()
    {
        parent::boot();

        static::deleting(function ($data) {
            $data->children()->delete();
        });
    }

    public function parent()
    {
        return $this->belongsTo(self::class, 'parent')->where('parent', null);
    }

    public function children()
    {
        return $this->hasMany(self::class, 'parent');
    }
}