Creating, Updating, and Deleting Data

After you have modeled your entity in a Java class, you can use it to create, update, or delete records for that entity type. First, you must get an EntityManager instance.

Using an EntityManager

An EntityManager instance is used to manage the state and life cycle of objects within a persistence unit. The entity manager is responsible for creating and removing persistent entity instances and finding entities by their primary key or other query criteria.

You access an entity manager by first creating an instance of an EntityManagerFactory object for a persistence unit defined in persistence.xml. Using the factory class, you can then create an EntityManager object.

The following sample creates an entity manager. The details of interacting with your data after creating the entity manager are omitted.

private void setupEntityManager(String persistenceUnitName)
{
    EntityManagerFactory factory =
        Persistence.createEntityManagerFactory(persistenceUnitName);
    EntityManager em = factory.createEntityManager();

    try {
        // Use the entity manager to interact with your data

    }
    catch (PersistenceException pex) {
        pex.printStackTrace();
    }
    finally {
        em.close();
    }
}

Persisting Records

After you have instantiated an EntityManager, you can create, update, or delete records for entities with an associated Java class.

Caution: To update or remove a record, you must first use the find() method to get the corresponding object and then call merge() or remove() in the same transaction. If you use a constructor to create an object and call setId() to identify the record instead of calling find(), the existing record will not be updated with a merge() call or deleted with a remove() call.

Here is a trivial sample that creates, updates, and then deletes a record for a Student entity. For more information on transactions, see Transactions.

private void sampleCreateUpdateDelete(String persistenceUnitName)
{
    EntityManagerFactory factory =
        Persistence.createEntityManagerFactory(persistenceUnitName);
    EntityManager em = factory.createEntityManager();

    EntityTransaction tx;
    try {
        // Create a student object
        Student student = new Student();
        student.setFirstName("Fabio");
        student.setLastName("Socrates");
        student.setEmail("socrates@salesforcetest123.com");
        Calendar cal = Calendar.getInstance();
        cal.set(1990, 5, 1, 0, 0, 0);
        cal.set(Calendar.MILLISECOND, 0);// We do not preserve ms resolution
        Date dob = cal.getTime();
        student.setDateOfBirth(dob);

        // Instantiate a transaction
        tx = em.getTransaction();
        // Start the transaction for creating a new record
        tx.begin();
        em.persist(student);
        tx.commit();

        tx = em.getTransaction();
        tx.begin();
        // Read back the object
        // Note: you should execute find() and remove() in the same transaction
        Student foundStudent = em.find(Student.class, student.getId());

        // Now update the email field for the record
        foundStudent.setEmail(fabio.socrates@salesforcetest.com);
        em.merge(foundStudent);

        // Finally, delete the record
        em.remove(foundStudent);
        tx.commit();

    }
    catch (PersistenceException pex) {
        pex.printStackTrace();
    }
    finally {
        em.close();
        tx.rollback();
    }
}

Note: Each custom Java entity has a name field. If you create a record that doesn't have a name value, the ID of the record is inserted as its name.