CODEWITHSUNDEEP
jpatransactionsspring-data-jpaentitymanagerspring-transactions
ako
ako

Reputation: 420

Does spring data jpa create new instance of EntityManager for each transaction?

I can't find information about relationship between EntityManager and transactions in spring data jpa application.

Which one of the statements is correct:

  1. new instance of EntityManager is created per transaction
  2. one shared instance of EntityManager is used for all transactions

Upvotes: 4

Views: 2283

Answers (1)

Dazak
Dazak

Reputation: 1033

The correct answer is: one shared instance of EntityManager is used for all transactions in the same persistence context.

We can have in consideration two things here:

First, the definition in the EntityManager Interface

An EntityManager instance is associated with a persistence context. A persistence context is a set of entity instances in which for any persistent entity identity there is a unique entity instance. Within the persistence context, the entity instances and their lifecycle are managed.

The set of entities that can be managed by a given EntityManager instance is defined by a persistence unit. A persistence unit defines the set of all classes that are related or grouped by the application, and which must be colocated in their mapping to a single database.

Second, the constructor of the Spring SimpleJpaRepository:

public SimpleJpaRepository(JpaEntityInformation<T, ?> entityInformation, EntityManager entityManager) {


    Assert.notNull(entityInformation, "JpaEntityInformation must not be null!");
    Assert.notNull(entityManager, "EntityManager must not be null!");


    this.entityInformation = entityInformation;
    this.em = entityManager;
    this.provider = PersistenceProvider.fromEntityManager(entityManager);
}

em is an attribute defined in that class with the final modifier:

private final EntityManager em;

And in the methods of the SimpleJpaRepository are made calls to that em without create new instances of the EntityManager.

Upvotes: 1

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