To return user defined objects (not entities) as query results we can use CriteriaBuilder#construct():
<Y> CompoundSelection<Y> construct(Class<Y> resultClass, Selection<?>... selections);
For example:
CriteriaQuery<EmployeeInfo> query = criteriaBuilder.createQuery(EmployeeInfo.class);
Root<Employee> employee = query.from(Employee.class);
query.select(criteriaBuilder.construct(EmployeeInfo.class, employee.get(Employee_.name),
employee.get(Employee_.salary)));
List<EmployeeInfo> resultList = entityManager.createQuery(query).getResultList();
Criteriabuilder#construct() is equivalent to JPQL constructor expressions.
Alternatively we can use CriteriaQuery#multiselect():
CriteriaQuery<EmployeeInfo> query = cb.createQuery(EmployeeInfo.class);
Root<Employee> employee = query.from(Employee.class);
query.multiselect(employee.get(Employee_.name), employee.get(Employee_.salary));
List<EmployeeInfo> resultList = em.createQuery(query).getResultList();
According to CriteriaQuery#multiselect(selections) document:
If the type of the criteria query is CriteriaQuery<X> for some user-defined class X (i.e., a criteria query object created by passing a X class argument to the createQuery method), the arguments to the multiselect method will be passed to the X constructor and an instance of type X will be returned for each row.
If the type of the criteria query is CriteriaQuery<X[]> for some class X, an instance of type X[] will be returned for each row. The elements of the array will correspond to the arguments of the multiselect method, in the specified order.
Example
Entity
@Entity
public class Employee {
@Id
@GeneratedValue
private long id;
private String name;
private double salary;
private String dept;
.............
}
Non-entity user defined class
public class EmployeeInfo {
private String name;
private double salary;
public EmployeeInfo(String name, double salary) {
this.name = name;
this.salary = salary;
}
.............
}
Using construct() method
public class ExampleMain {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
persistEmployees();
findAllEmployeeEntities();
findEmployeeInfo();
findEmployeeInfo2();
} finally {
entityManagerFactory.close();
}
}
public static void persistEmployees() {
Employee employee1 = Employee.create("Diana", 2000, "IT");
Employee employee2 = Employee.create("Rose", 4500, "Admin");
Employee employee3 = Employee.create("Denise", 2000, "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();
em.close();
}
private static void findAllEmployeeEntities() {
System.out.println("-- finding Employee entities - entity selection --");
EntityManager em = entityManagerFactory.createEntityManager();
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Employee> query = cb.createQuery(Employee.class);
Root<Employee> employee = query.from(Employee.class);
query.select(employee);
TypedQuery<Employee> typedQuery = em.createQuery(query);
List<Employee> resultList = typedQuery.getResultList();
resultList.forEach(System.out::println);
em.close();
}
private static void findEmployeeInfo() {
System.out.println("-- EmployeeInfo - using construct() --");
EntityManager em = entityManagerFactory.createEntityManager();
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<EmployeeInfo> query = cb.createQuery(EmployeeInfo.class);
Root<Employee> employee = query.from(Employee.class);
query.select(cb.construct(EmployeeInfo.class, employee.get(Employee_.name),
employee.get(Employee_.salary)));
TypedQuery<EmployeeInfo> typedQuery = em.createQuery(query);
List<EmployeeInfo> resultList = typedQuery.getResultList();
resultList.forEach(System.out::println);
em.close();
}
private static void findEmployeeInfo2() {
System.out.println("-- EmployeeInfo - using multiselect() --");
EntityManager em = entityManagerFactory.createEntityManager();
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<EmployeeInfo> query = cb.createQuery(EmployeeInfo.class);
Root<Employee> employee = query.from(Employee.class);
query.multiselect(employee.get(Employee_.name),
employee.get(Employee_.salary));
TypedQuery<EmployeeInfo> typedQuery = em.createQuery(query);
List<EmployeeInfo> resultList = typedQuery.getResultList();
resultList.forEach(System.out::println);
em.close();
}
}-- finding Employee entities - entity selection --
Employee{id=1, name='Diana', salary=2000.0, dept='IT'}
Employee{id=2, name='Rose', salary=4500.0, dept='Admin'}
Employee{id=3, name='Denise', salary=2000.0, dept='Admin'}
Employee{id=4, name='Mike', salary=4000.0, dept='IT'}
Employee{id=5, name='Linda', salary=4500.0, dept='Sales'}
-- EmployeeInfo - using construct() --
EmployeeInfo{name='Diana', salary=2000.0}
EmployeeInfo{name='Rose', salary=4500.0}
EmployeeInfo{name='Denise', salary=2000.0}
EmployeeInfo{name='Mike', salary=4000.0}
EmployeeInfo{name='Linda', salary=4500.0}
-- EmployeeInfo - using multiselect() --
EmployeeInfo{name='Diana', salary=2000.0}
EmployeeInfo{name='Rose', salary=4500.0}
EmployeeInfo{name='Denise', salary=2000.0}
EmployeeInfo{name='Mike', salary=4000.0}
EmployeeInfo{name='Linda', salary=4500.0}
Example ProjectDependencies and Technologies Used: - h2 1.4.197: H2 Database Engine.
- hibernate-core 5.3.2.Final: Hibernate's core ORM functionality.
Implements javax.persistence:javax.persistence-api version 2.2 - hibernate-jpamodelgen 5.3.2.Final: Annotation Processor to generate JPA 2 static metamodel classes.
- JDK 1.8
- Maven 3.5.4
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