Codeigniter 4.2 with Eloquent ORM

composer require "illuminate/database"
composer require "illuminate/events"

Config/Events.php

use Illuminate\Database\Capsule\Manager as Capsule;
use Illuminate\Events\Dispatcher;
use Illuminate\Container\Container;

function boostEloquent() {
  $capsule = new Capsule;

  $capsule->addConnection([
    'driver' => 'mysql',
    'host' => 'localhost',
    'database' => 'database',
    'username' => 'root',
    'password' => 'password',
    'charset' => 'utf8',
    'collation' => 'utf8_unicode_ci',
    'prefix' => '',
  ]);

  // Set the event dispatcher used by Eloquent models... (optional)
  $capsule->setEventDispatcher(new Dispatcher(new Container));

  // Make this Capsule instance available globally via static methods... (optional)
  $capsule->setAsGlobal();

  // Setup the Eloquent ORM... (optional; unless you've used setEventDispatcher())
  $capsule->bootEloquent();
}

Events::on('pre_system', function () {
    boostEloquent();

    if (ENVIRONMENT !== 'testing')
    ...
}

https://www.modb.pro/db/49966

Codeigniter 4 ORM relation By hand Part 2

Modify 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));
    }
    
    // copy self object return ORM Object
    public function cso() 
    {
        $class_name = get_class($this);
        $class_new_object = (new $class_name);
        $class_new_object->builder = clone $this->builder;
        return $class_new_object;
    }

    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);
    }
}

App\Controllers\OrderListContriller.php

namespace App\Controllers\Order;

class OrderListController extends \App\Controllers\BaseController
{
  public function OrderList()
  {
      // 3. 
      $order = (new Order)->where("id", $order_id);
      $orderData = $order->cso()->findAll(); // Maybe need orderData to do something.

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

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