In JPQL, a constructor can be used in the SELECT clause to return an instance of a non-entity Java object. For example:

  Query query = em.createQuery("SELECT NEW com.example.MyClass(e.attribute1, e.attribute2...) FROM MyEntity e");
  List<MyClass> resultList = query.getResultList();

Example

Entity

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private long salary;
    private String dept;
    .............
}

Object to be selected

public class EmployeeNameSalaryPair {
    private String name;
    private long salary;

    public EmployeeNameSalaryPair(String name, long salary) {
        this.name = name;
        this.salary = salary;
    }
    .............
}

Executing Query with Constructor Expression

Following example retrieves employee name-salary pairs both as Object[] and as EmployeeNameSalaryPair:

public class ExampleMain {
    private static EntityManagerFactory entityManagerFactory =
            Persistence.createEntityManagerFactory("example-unit");

    public static void main(String[] args) {
        try {
            persistEmployees();
            getNameSalaryPairsAsObjectArray();
            getNameSalaryPairsViaConstructorExpression();

        } finally {
            entityManagerFactory.close();
        }
    }

    public static void persistEmployees() {
        Employee employee1 = Employee.create("Diana", 2000, "IT");
        Employee employee2 = Employee.create("Rose", 3500, "Admin");
        Employee employee3 = Employee.create("Denise", 2500, "Admin");
        Employee employee4 = Employee.create("Mike", 4000, "IT");
        Employee employee5 = Employee.create("Linda", 4500, "Sales");
        EntityManager em = entityManagerFactory.createEntityManager();
        em.getTransaction().begin();
        em.persist(employee1);
        em.persist(employee2);
        em.persist(employee3);
        em.persist(employee4);
        em.persist(employee5);
        em.getTransaction().commit();

        System.out.println("-- employee persisted --");
        em.createQuery("Select e from Employee e")
          .getResultList()
          .forEach(System.out::println);
        em.close();
    }

    private static void getNameSalaryPairsAsObjectArray() {
        System.out.println("-- Employee name salary pair as Object[] --");
        EntityManager em = entityManagerFactory.createEntityManager();
        Query query = em.createQuery("SELECT e.name, e.salary FROM Employee e");
        List<Object[]> resultList = query.getResultList();
        resultList.forEach(arr -> System.out.println(Arrays.toString(arr)));
        em.close();
    }

    private static void getNameSalaryPairsViaConstructorExpression() {
        System.out.println("-- Employee name salary pair as EmployeeNameSalaryPair --");
        EntityManager em = entityManagerFactory.createEntityManager();
        Query query =
                em.createQuery("SELECT NEW com.logicbig.example.EmployeeNameSalaryPair(e.name, e.salary)"
                + " FROM Employee e");
        List<EmployeeNameSalaryPair> resultList = query.getResultList();
        resultList.forEach(System.out::println);
        em.close();
    }
}

-- employee persisted --
Employee{id=1, name='Diana', salary=2000, dept='IT'}
Employee{id=2, name='Rose', salary=3500, dept='Admin'}
Employee{id=3, name='Denise', salary=2500, dept='Admin'}
Employee{id=4, name='Mike', salary=4000, dept='IT'}
Employee{id=5, name='Linda', salary=4500, dept='Sales'}
-- Employee name salary pair as Object[] --
[Diana, 2000]
[Rose, 3500]
[Denise, 2500]
[Mike, 4000]
[Linda, 4500]
-- Employee name salary pair as EmployeeNameSalaryPair --
EmployeeNameSalaryPair{name='Diana', salary=2000}
EmployeeNameSalaryPair{name='Rose', salary=3500}
EmployeeNameSalaryPair{name='Denise', salary=2500}
EmployeeNameSalaryPair{name='Mike', salary=4000}
EmployeeNameSalaryPair{name='Linda', salary=4500}

Example Project

Dependencies and Technologies Used:

• h2 1.4.197: H2 Database Engine.
• hibernate-core 5.3.1.Final: Hibernate's core ORM functionality.
  Implements javax.persistence:javax.persistence-api version 2.2
• JDK 1.8
• Maven 3.5.4