weixin/app/Repositories/Models/Exam/BankCategory.php

<?php

namespace App\Repositories\Models\Exam;

use App\Repositories\Models\Model;
use Illuminate\Support\Facades\DB;

class BankCategory extends Model
{
    /**
     * @var string
     */
    protected $table = 'exam_bank_categories';

    protected $guarded = [];

    /**
     * The attributes excluded from the model's JSON form.
     *
     * @var array
     */
    protected $hidden = [];

    public static function boot()
    {
        parent::boot(); // TODO: Change the autogenerated stub
        self::updated(function (BankCategory $bankCategory) {
            if ($bankCategory->isDirty('pid')) {
                $nodes = self::byIdGetParentIds($bankCategory->id);
                $nodes = '-' . arr2str($nodes, '-') . '-';
                DB::table('exam_bank_categories')->where('id', $bankCategory->id)->update(['nodes' => $nodes]);
            }
        });
    }

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

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

    public function setNodesAttribute($val)
    {
        $val = arr2str($val, '-');
        $this->attributes['nodes'] = "-{$val}-";
    }

    public static function byIdGetParentIds($id)
    {
        $ids = [$id];
        $pid = self::query()->where('id', $id)->value('pid');
        if ($pid) {
            $pid = self::byIdGetParentIds($pid);
            $ids = array_merge($ids, $pid);
        }

        return $ids;
    }
}