In Criteria API, a CriteriaQuery , CriteriaUpdate , or CriteriaDelete object may be modified, either before or after Query or TypedQuery objects have been created and executed from it.
Quick Example
.........
CriteriaQuery<Object[]> criteriaQuery = criteriaBuilder.createQuery(Object[].class);
Root<Employee> root = criteriaQuery.from(Employee.class);
//Employees name and salary
criteriaQuery.multiselect(root.get(Employee_.NAME), root.get(Employee_.SALARY));
List<Object[]> resultList = entityManager.createQuery(criteriaQuery).getResultList();
resultList.forEach(arr -> System.out.println(Arrays.toString(arr)));
//Employees name and dept
criteriaQuery.multiselect(root.get(Employee_.NAME), root.get(Employee_.DEPT));
List<Object[]> resultList2 = entityManager.createQuery(criteriaQuery).getResultList();
resultList2.forEach(arr -> System.out.println(Arrays.toString(arr)));
.....
Complete Example
Entity
@Entity
public class Employee {
@Id
@GeneratedValue
private long id;
private String name;
private double salary;
private String dept;
.............
}
Reusing Query Object
public class ExampleMain {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
persistEmployees();
findEmployees();
findEmployees2();
} finally {
entityManagerFactory.close();
}
}
private static void findEmployees() {
EntityManager entityManager = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = criteriaBuilder.createQuery(Employee.class);
Root<Employee> root = criteriaQuery.from(Employee.class);
criteriaQuery.select(root);
System.out.println("-- All employees --");
List<Employee> resultList = entityManager.createQuery(criteriaQuery).getResultList();
resultList.forEach(System.out::println);
System.out.println("-- All employees from IT dept --");
criteriaQuery.where(criteriaBuilder.equal(root.get(Employee_.DEPT), "IT"));
List<Employee> resultList2 = entityManager.createQuery(criteriaQuery).getResultList();
resultList2.forEach(System.out::println);
entityManager.close();
}
private static void findEmployees2() {
EntityManager entityManager = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Object[]> criteriaQuery = criteriaBuilder.createQuery(Object[].class);
Root<Employee> root = criteriaQuery.from(Employee.class);
System.out.println("-- Employees name and salary --");
criteriaQuery.multiselect(root.get(Employee_.NAME), root.get(Employee_.SALARY));
List<Object[]> resultList = entityManager.createQuery(criteriaQuery).getResultList();
resultList.forEach(arr -> System.out.println(Arrays.toString(arr)));
System.out.println("-- Employees name and dept --");
criteriaQuery.multiselect(root.get(Employee_.NAME), root.get(Employee_.DEPT));
List<Object[]> resultList2 = entityManager.createQuery(criteriaQuery).getResultList();
resultList2.forEach(arr -> System.out.println(Arrays.toString(arr)));
entityManager.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();
em.close();
}
} -- All employees -- Employee{id=1, name='Diana', salary=2000.0, dept='IT'} Employee{id=2, name='Rose', salary=3500.0, dept='Admin'} Employee{id=3, name='Denise', salary=2500.0, dept='Admin'} Employee{id=4, name='Mike', salary=4000.0, dept='IT'} Employee{id=5, name='Linda', salary=4500.0, dept='Sales'} -- All employees from IT dept -- Employee{id=1, name='Diana', salary=2000.0, dept='IT'} Employee{id=4, name='Mike', salary=4000.0, dept='IT'} -- Employees name and salary -- [Diana, 2000.0] [Rose, 3500.0] [Denise, 2500.0] [Mike, 4000.0] [Linda, 4500.0] -- Employees name and dept -- [Diana, IT] [Rose, Admin] [Denise, Admin] [Mike, IT] [Linda, Sales]
Example ProjectDependencies and Technologies Used: - h2 1.4.199: H2 Database Engine.
- hibernate-core 5.4.2.Final: Hibernate's core ORM functionality.
Implements javax.persistence:javax.persistence-api version 2.2 - hibernate-jpamodelgen 5.4.2.Final: Annotation Processor to generate JPA 2 static metamodel classes.
- JDK 1.8
- Maven 3.5.4
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