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Blending the ORM and MongoDB ODM

This article demonstrates how you can integrate the Doctrine MongoDB ODM and the ORM transparently, maintaining a clean domain model. This is something that is supported indirectly by the libraries by using the events.

This example will have a Product that is stored in MongoDB and the Order stored in a SQL database like MySQL, PostgreSQL or SQLite.

Define Product

First lets define our Product document:

1<?php

namespace Documents;

#[Document]
class Product
{
    #[Id]
    public string $id;

    #[Field(type: 'string')]
    public string $title;
}


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Define Entity

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

1<?php

namespace Entities;

use Documents\Product;

#[Entity]
#[Table(name: 'orders')]
class Order
{
    #[Id]
    #[Column(type: 'int')]
    #[GeneratedValue(strategy: 'AUTO')]
    public int $id;

    #[Column(type: 'string')]
    private string $productId;

    private Product $product;

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

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

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

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


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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:

1<?php

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


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or in YAML configuration of the Symfony container:

1App\Listeners\MyEventSubscriber:
    tags:
        - { name: doctrine.event_listener, connection: default, event: postLoad }


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

1<?php

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

class MyEventSubscriber
{
    public function __construct(
        private readonly DocumentManager $dm,
    ) {}

    public function postLoad(LifecycleEventArgs $eventArgs): void
    {
        $order = $eventArgs->getEntity();

        if (!$order instanceof Order) {
            return;
        }

        $product = $this->dm->getReference(Product::class, $order->getProductId());

        $eventArgs->getObjectManager()
            ->getClassMetadata(Order::class)
            ->reflClass
            ->getProperty('product')
            ->setValue($order, $product);
    }
}


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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. Please note, that the event subscriber will be called on postLoad for all entities that are loaded by doctrine. Thus, it is recommended to check for the current entity.

Working with Products and Orders

First create a new Product:

1<?php

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


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

1<?php

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


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

1<?php

$order = $em->find(Order::class, $order->id);

$product = $order->getProduct();

echo "Order Title: " . $product->title;


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

1<?php

print_r($order);


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The above would output the following:

1Order 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
        )
)


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