The persistence of entities in a database is managed by the entity manager in Symfony. Entities may be added to, changed, removed, and retrieved from the database. It might be a bad decision to use the entity manager in your application, regardless how convenient it is. This article will explain why using explicit entity repositories rather than the entity manager is typically seen to be a preferable practice.

Let's first define what "explicit entity repositories" are. An entity repository in Symfony is a class created specifically to deal with the persistence of a certain entity type. It serves as an intermediate layer between your application and the database, enabling you to create original queries and actions tailored to your object. 

On the other hand, the entity manager is a generic tool that can be used to persist any entity. It's essentially a catch-all solution for handling database operations, and as such, it can become a bottleneck in your application. 

A typical usage of the Entity Manager in Symfony would look like this:

php
use Doctrine\ORM\EntityManagerInterface;

class SomeClass
{
    private $entityManager;

    public function __construct(EntityManagerInterface $entityManager)
    {
        $this->entityManager = $entityManager;
    }

    public function updateUserName($userId, $newName)
    {
        // Find a user by their ID
        $user = $this->entityManager->find(User::class, $userId);

        // Update the user's name
        $user->setName($newName);

        // Persist the changes to the database
        $this->entityManager->persist($user);
        $this->entityManager->flush();
    }
}

In this case, we would separately create the Repository Class. This is not only really poor design, but it will also make it much more difficult to apply changes to the repository as we are unable to utilize our IDE to resolve the Entities.


Using the entity manager might make your code more difficult to understand and maintain, which is one of the key reasons why doing so is a bad choice. Your code is closely tied to your application's persistence layer when you employ the entity manager. This can make it more challenging to comprehend what is occurring in your code and more challenging to modify how you persist your entities in the future. 

Using explicit entity repositories, on the other hand, decouples your code from the persistent layer. In addition to making it simpler to modify the way your entities are persistent in the future, this also makes it simpler to comprehend what is occurring in your code.

The entity manager should not be used for the additional reason that it may slow down your application. Since the entity manager is a universal tool that may be used to persist any entity, it must deal with a wide range of situations. This may result in slower performance, particularly if you have a lot of entities or are using the database a lot. 

On the other hand, explicit entity repositories are designed to handle the persistence of a specific entity type, and as such, they can be optimized for the specific needs of that entity. This can lead to faster performance, especially if you have a large number of entities or if you're performing a lot of database operations.

Certainly! Here is the revised code example that uses an explicit entity repository and does not use the entity manager:

php
use App\Repository\UserRepository;

class SomeClass
{
    private $userRepository;

    public function __construct(UserRepository $userRepository)
    {
        $this->userRepository = $userRepository;
    }

    public function updateUserName($userId, $newName)
    {
        // Find a user by their ID
        $user = $this->userRepository->find($userId);

        // Update the user's name
        $user->setName($newName);

        // Persist the changes to the database
        $this->userRepository->persist($user);
        $this->userRepository->flush();
    }
}

The 'SomeClass' class in this updated example no longer depends on the entity manager. Instead, it locates the user, modifies their name, and saves the changes to the database using the 'UserRepository'. As a result, you may handle all of the User entity's persistent logic without using the entity manager by using an explicit entity repository. We don't actually need to use the EntityManager at all because Symfony 6's Repository classes all have access to the necessary persistence functionalities. We may entirely rely on our explicit entity repositories to handle the task for us instead. Also, it will become clear for other developers what kind of transaction is going on here by looking at the property name instead of scanning the code for EntityManager declarations.

One final reason why using the entity manager is a bad idea is that it can make your code harder to test. When you use the entity manager, your code becomes tightly coupled to the persistence layer of your application, which can make it harder to mock or stub out the entity manager in your tests. On the other hand, when you use explicit entity repositories, your code becomes decoupled from the persistence layer, which makes it easier to mock or stub out the entity repository in your tests.

In conclusion, while the entity manager can be a convenient tool for handling the persistence of entities in a Symfony application, it's generally considered a bad idea to use it. Instead, it's generally a better practice to use explicit entity repositories, which can make your code easier to understand, maintain, and test, and can also lead to faster performance.