EntityManager manages the lifecycle of an entity and performs all operations associated with the entity.

EntityManager

Meaning

An entity manager manages the lifecycle of an entity and performs all operations associated with the entity. The entity manager performs operations such as storing an entity in a database or reading an entity from a database.

Key Features

The key features of an entity manager are as follows:

  1. Persist: Stores an entity in a database.
  2. Query: Reads an entity from a database.
  3. Update: Modifies an entity stored in a database.
  4. Delete: Removes an entity from a database.

Example

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@Repository
public class UserRepository {
    @PersistenceContext
    private EntityManager em;

    public void save(User user) {
        em.persist(user);
    }

    public User findById(Long id) {
        return em.find(User.class, id);
    }

    public void update(User user) {
        em.merge(user);
    }

    public void delete(User user) {
        em.remove(user);
    }
}

The entity manager can be injected using the @PersistenceContext annotation. The entity manager can be used to perform operations such as saving, querying, modifying, and deleting entities. The entity manager operates in a transaction unit, and the entity manager is automatically closed when the transaction ends.

Explanation of Usage Examples

The example above is the UserRepository class that uses EntityManager to manage the User entity.

  • The save method uses em.persist(user) to store a new user entity in the database.
  • The findById method uses em.find(User.class, id) to query the user entity with the given ID.
  • The update method uses em.merge(user) to modify an existing user entity.
  • The delete method uses em.remove(user) to delete the user entity.

Summary

  • An entity manager manages the lifecycle of an entity and performs all operations associated with the entity.
  • An entity manager operates in a transaction unit, and the entity manager is automatically closed when the transaction ends.
  • An entity manager can be injected using the @PersistenceContext annotation.