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Blending the ORM and MongoDB ODM

Since the start of the Doctrine MongoDB Object Document Mapper project people have asked how it can be integrated with the ORM. This article will demonstrates how you can integrate the two transparently, maintaining a clean domain model.

This example will have a `Product` that is stored in MongoDB and the `Order` stored in a MySQL database.

Define Product

First lets define our `Product` document:

<?php

namespace Documents;

/** @Document */
class Product
{
    /** @Id */
    private $id;

    /** @String */
    private $title;

    public function getId()
    {
        return $this->id;
    }

    public function getTitle()
    {
        return $this->title;
    }

    public function setTitle($title)
    {
        $this->title = $title;
    }
}

Define Entity

Next create the `Order` entity that has a `$product` and `$productId` property linking it to the `Product` that is stored with MongoDB:

<?php

namespace Entities;

use Documents\Product;

/**
 * @Entity
 * @Table(name="orders")
 */
class Order
{
    /**
     * @Id @Column(type="integer")
     * @GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @Column(type="string")
     */
    private $productId;

    /**
     * @var Documents\Product
     */
    private $product;

    public function getId()
    {
        return $this->id;
    }

    public function getProductId()
    {
        return $this->productId;
    }

    public function setProduct(Product $product)
    {
        $this->productId = $product->getId();
        $this->product = $product;
    }

    public function getProduct()
    {
        return $this->product;
    }
}

Event Subscriber

Now we need to setup an event subscriber that will set the `$product` property of all `Order` instances to a reference to the document product so it can be lazily loaded when it is accessed the first time. So first register a new event subscriber:

<?php

$eventManager = $em->getEventManager();
$eventManager->addEventListener(
    array(\Doctrine\ORM\Events::postLoad), new MyEventSubscriber($dm)
);

So now we need to define a class named `MyEventSubscriber` and pass a dependency to the `DocumentManager`. It will have a `postLoad()` method that sets the product document reference:

<?php

use Doctrine\ODM\MongoDB\DocumentManager;
use Doctrine\ORM\Event\LifecycleEventArgs;

class MyEventSubscriber
{
    public function __construct(DocumentManager $dm)
    {
        $this->dm = $dm;
    }

    public function postLoad(LifecycleEventArgs $eventArgs)
    {
        $order = $eventArgs->getEntity();
        $em = $eventArgs->getEntityManager();
        $productReflProp = $em->getClassMetadata('Entities\Order')
            ->reflClass->getProperty('product');
        $productReflProp->setAccessible(true);
        $productReflProp->setValue(
            $order, $this->dm->getReference('Documents\Product', $order->getProductId())
        );
    }
}

The `postLoad` method will be invoked after an ORM entity is loaded from the database. This allows us to use the `DocumentManager` to set the `$product` property with a reference to the `Product` document with the product id we previously stored.

Working with Products and Orders

First create a new `Product`:

<?php

$product = new \Documents\Product();
$product->setTitle('Test Product');
$dm->persist($product);
$dm->flush();

Now create a new `Order` and link it to a `Product` in MySQL:

<?php

$order = new \Entities\Order();
$order->setProduct($product);
$em->persist($order);
$em->flush();

Later we can retrieve the entity and lazily load the reference to the document in MongoDB:

<?php

$order = $em->find('Order', $order->getId());

// Instance of an uninitialized product proxy
$product = $order->getProduct();

// Initializes proxy and queries the database
echo "Order Title: " . $product->getTitle();

If you were to print the `$order` you would see that we got back regular PHP objects:

<?php

print_r($order);

The above would output the following:

Order Object
(
    [id:Entities\Order:private] => 53
    [productId:Entities\Order:private] => 4c74a1868ead0ed7a9000000
    [product:Entities\Order:private] => Proxies\DocumentsProductProxy Object
        (
            [__isInitialized__] => 1
            [id:Documents\Product:private] => 4c74a1868ead0ed7a9000000
            [title:Documents\Product:private] => Test Product
        )
)