Codeigniter 4 ORM relation By hand

Add ModelTrait file at \App\Traits

namespace App\Traits;

trait ModelTrait
{
    // fetaure Maybe belongsTo

    // get result but not effect this, keep this ORM status
    public function newSelfObject()
    {
        return $this->db->query($this->builder->getCompiledSelect(false));
    }

    public function hasOne($class, $relation_primary_key=null, $primary_key=null)
    {
        return $class->where($relation_primary_key ?? $this->primaryKey, $this->newSelfObject()->getRowArray()[$primary_key ?? $this->primaryKey] ?? '');
    }

    // whereIn  If can't get records, return null.  Usually use primaryKey cloud happen
    public function hasMany($class, $relation_primary_key=null, $primary_key=null)
    {
        $temp = array_column($this->newSelfObject()->getResult(), $primary_key ?? $this->primaryKey);
        return $class->whereIn($relation_primary_key ?? $this->primaryKey, empty($temp) ? [null] : $temp);
    }
}

How to use

App\Models\Order.php

class Order extends Model
{
    use ModelTrait;

    protected $table      = 'order';
    protected $primaryKey = 'order_id';
    
    public function members()
    {
        return $this->hasMany(new Member);
        
        // OR
        return $this->hasMany(new Member, 'id', 'member_id'); // id always use new Member,  member_id use Order
    }

App\Controllers\OrderListContriller.php

namespace App\Controllers\Order;

class OrderListController extends \App\Controllers\BaseController
{
  public function OrderList()
  {
      // 1. one order
      $members = (new Order)->where('id', $order_id)->members()->first(); // ->findAll();

      // 2. All orders
      $members = (new Order)->members()->findAll();

      // 3. 
      $order = (new Order)->where("id", $order_id);
      $orderData = $order->newSelfObject()->getRow(); // Maybe need orderData to do something.

      $member = $order->members()->where('createtime >', '2022/11/22')->first(); // ->findAll();
  }
}

You can make belongTo or belongsTo by yourself. More about feature like multiple key, it's more complex