Symfony Doctrine does not hydrate the whole chain - php

Question

I simplified my 3 entities as much as possible below, it shows a simple relationship of Currency <- 1:1 -> Balance <- 1:N -> BalanceLog
Entity/Currency.php
/**
* #ORM\Entity(repositoryClass=CurrencyRepository::class)
*/
class Currency
{
/**
* #ORM\Id
* #ORM\Column(type="string", length=3)
*/
private ?string $code;
/**
* #ORM\OneToOne(targetEntity="Balance", mappedBy="currency")
**/
private ?Balance $balance;
// ...
}
Entity/Balance.php
/**
* #ORM\Entity(repositoryClass=BalanceRepository::class)
*/
class Balance
{
/**
* #ORM\Id
* #ORM\OneToOne(targetEntity="Currency", inversedBy="balance")
* #ORM\JoinColumn(name="currency", referencedColumnName="code", nullable=false)
**/
private ?Currency $currency;
/**
* #ORM\OneToMany(targetEntity="App\Entity\BalanceLog", mappedBy="balance")
*/
private Collection $balance_logs;
// ...
}
Entity/BalanceLog.php
/**
* #ORM\Entity(repositoryClass=BalanceLogRepository::class)
*/
class BalanceLog
{
/**
* #ORM\Id
* #ORM\GeneratedValue
* #ORM\Column(type="integer")
*/
private ?int $id;
/**
* #ORM\ManyToOne(targetEntity="App\Entity\Balance", inversedBy="balance_logs")
* #ORM\JoinColumn(name="balance_currency", referencedColumnName="currency")
**/
private ?Balance $balance;
// ...
}
The issue happens when I call:
$balanceLog = $this->getDoctrine()
->getRepository('App:BalanceLog')->findAll();
This hydrates the BalanceLog::$balance to the proper instance of Balance type, but it does not hydrate the BalanceLog::$balance->currency to Currency instance. Instead it wants to use string only
Resulting in error:
Typed property App\Entity\Balance::$currency must be an instance of App\Entity\Currency or null, string used
The dirty fix is to make Balance::$currency without fixed type of ?Currency. Then it will accept string and the code "works". But it is not correct. The Balance::$currency should be of Currency type, not sometimes string, sometimes currency.
I tried to make my own method in BalanceLogRepository, and for whatever reason this works just fine:
public function findByBalance(Balance $balance) : iterable
{
$query = $this->createQueryBuilder('bl');
$query->andWhere('bl.balance = :balance')
->setParameter('balance', $balance);
return $query->getQuery()->getResult();
}
So I am even more perplexed as to why the default findAll or findBy does not do recursive hydration
After further investigation I found a very weird behavior:
if I prepend this code:
$balance = $this->getDoctrine()->getRepository('App:Balance')->find('USD');
in front of
$balanceLog = $this->getDoctrine()->getRepository('App:BalanceLog')->findAll();
in my controller, then the error is gone. Its as if the App:Balance ORM schema of Balance with dependencies were not properly loaded until I try to fetch the Balance object directly apriori.

Answer 1

I did some debugging and it looks that BalanceLog does not create a full Balance Entity instance, but instead a Proxy. The solution was to add eager loading to the BalanceLog class
class BalanceLog
{
/**
* #ORM\Id
* #ORM\GeneratedValue
* #ORM\Column(type="integer")
*/
private ?int $id;
/**
* #ORM\ManyToOne(targetEntity="App\Entity\Balance", inversedBy="balance_logs", fetch="EAGER")
* #ORM\JoinColumn(name="balance_currency", referencedColumnName="currency")
**/
private ?Balance $balance;
// ...
}
The UnitOfWork.php then does not use Proxy but instead loads the Entity as a whole.
If somebody wonders why querying Balance beforehand made the code work, its because of sophisticated caching mechanism of Doctrine. It saved Balance instance for primary key USD and then when BalanceLog was populated, it used this instance instead of creating a Proxy.
I still think that Proxy should not enforce strictly typed property from Entity though, but this is something for Doctrine developers to decide.