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JPQL IS EMPTY Expression

[Updated: May 16, 2018, Created: May 16, 2018]

This example shows how to use IS EMPTY comparison expression which tests whether a collection-valued relationship has been set.

Examples

Entities

@Entity
public class Employee {
  @Id
  @GeneratedValue
  private long id;
  private String name;
  @ManyToMany(cascade = CascadeType.ALL)
  private List<Task> tasks;
    .............
}
@Entity
public class Task {
  @Id
  @GeneratedValue
  private long id;
  private String description;
  private String supervisor;
    .............
}

Using IS EMPTY

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

  public static void main(String[] args) {
      try {
          persistEmployees();
          findEmployeeWithNoTask();
          findEmployeeWithTasks();
          findEmployeeWithNoTaskSupervisor();
      } finally {
          entityManagerFactory.close();
      }
  }

  public static void persistEmployees() {
      Task task1 = new Task("Coding", "Denise");
      Task task2 = new Task("Refactoring", "Rose");
      Task task3 = new Task("Designing", "Denise");
      Task task4 = new Task("Documentation", null);

      Employee employee1 = Employee.create("Diana", task1, task3);
      Employee employee2 = Employee.create("Mike");
      Employee employee3 = Employee.create("Tim", task2, task4);
      Employee employee4 = Employee.create("Jack");

      EntityManager em = entityManagerFactory.createEntityManager();
      em.getTransaction().begin();
      em.persist(employee1);
      em.persist(employee2);
      em.persist(employee3);
      em.persist(employee4);
      em.getTransaction().commit();
      em.close();
      System.out.println("-- Employee persisted --");
      System.out.println(employee1);
      System.out.println(employee2);
      System.out.println(employee3);
      System.out.println(employee4);
  }

  private static void findEmployeeWithNoTask() {
      System.out.println("-- Employees with no tasks --");
      EntityManager em = entityManagerFactory.createEntityManager();
      Query query = em.createQuery("SELECT e FROM Employee e where e.tasks is EMPTY");
      List<Employee> resultList = query.getResultList();
      resultList.forEach(System.out::println);
      em.close();
  }

  private static void findEmployeeWithTasks() {
      System.out.println("-- Employees with tasks --");
      EntityManager em = entityManagerFactory.createEntityManager();
      Query query = em.createQuery("SELECT e FROM Employee e where e.tasks is NOT EMPTY");
      List<Employee> resultList = query.getResultList();
      resultList.forEach(System.out::println);
      em.close();
  }

  private static void findEmployeeWithNoTaskSupervisor() {
      System.out.println("-- Employees with no task supervisor --");
      EntityManager em = entityManagerFactory.createEntityManager();
      //IS EMPTY is used for collections only. To find employee with task having no supervisor use a join
      Query query = em.createQuery("SELECT DISTINCT e FROM Employee e INNER JOIN e.tasks t "
              + "where t.supervisor is NULL");
      List<Employee> resultList = query.getResultList();
      resultList.forEach(System.out::println);
      em.close();
  }
}
-- Employee persisted --
Employee{id=1, name='Diana', tasks=[Task{id=2, description='Coding', supervisor='Denise'}, Task{id=3, description='Designing', supervisor='Denise'}]}
Employee{id=4, name='Mike', tasks=[]}
Employee{id=5, name='Tim', tasks=[Task{id=6, description='Refactoring', supervisor='Rose'}, Task{id=7, description='Documentation', supervisor='null'}]}
Employee{id=8, name='Jack', tasks=[]}
-- Employees with no tasks --
Employee{id=4, name='Mike', tasks=[]}
Employee{id=8, name='Jack', tasks=[]}
-- Employees with tasks --
Employee{id=1, name='Diana', tasks=[Task{id=2, description='Coding', supervisor='Denise'}, Task{id=3, description='Designing', supervisor='Denise'}]}
Employee{id=5, name='Tim', tasks=[Task{id=6, description='Refactoring', supervisor='Rose'}, Task{id=7, description='Documentation', supervisor='null'}]}
-- Employees with no task supervisor --
Employee{id=5, name='Tim', tasks=[Task{id=6, description='Refactoring', supervisor='Rose'}, Task{id=7, description='Documentation', supervisor='null'}]}

Example Project

Dependencies and Technologies Used:

  • h2 1.4.197: H2 Database Engine.
  • hibernate-core 5.2.13.Final: The core O/RM functionality as provided by Hibernate.
    Implements javax.persistence:javax.persistence-api version 2.1
  • JDK 1.8
  • Maven 3.3.9

JPQL IS EMPTY Expression Select All Download
  • jpql-is-empty-example
    • src
      • main
        • java
          • com
            • logicbig
              • example
                • ExampleMain.java
          • resources
            • META-INF

    See Also