Following example shows how to use CriteriaBuilder.isEmpty() and CriteriaBuilder.isNotEmpty() methods.
IsEmpty() method creates a predicate that tests whether a collection is empty.
<C extends Collection<?>> Predicate isEmpty(Expression<C> collection);
<C extends Collection<?>> Predicate isNotEmpty(Expression<C> collection);
Quick Example:
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = criteriaBuilder.createQuery(Employee.class);
Root<Employee> employee = criteriaQuery.from(Employee.class);
criteriaQuery.select(employee)
.where(criteriaBuilder.isEmpty(employee.get(Employee_.tasks)));
TypedQuery<Employee> typedQuery = entityManager.createQuery(criteriaQuery);
List<Employee> list = typedQuery.getResultList();
Complete Example
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;
.............
}
Applying isEmpty() and isNotEmpty() predicates
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();
}
}
private static void findEmployeeWithNoTask() {
System.out.println("-- Employees with no tasks --");
EntityManager em = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = criteriaBuilder.createQuery(Employee.class);
Root<Employee> employee = criteriaQuery.from(Employee.class);
criteriaQuery.select(employee)
.where(criteriaBuilder.isEmpty(employee.get(Employee_.tasks)));
TypedQuery<Employee> typedQuery = em.createQuery(criteriaQuery);
typedQuery.getResultList().forEach(System.out::println);
em.close();
}
private static void findEmployeeWithTasks() {
System.out.println("-- Employees with tasks --");
EntityManager em = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = criteriaBuilder.createQuery(Employee.class);
Root<Employee> employee = criteriaQuery.from(Employee.class);
criteriaQuery.select(employee)
.where(criteriaBuilder.isNotEmpty(employee.get(Employee_.tasks)));
TypedQuery<Employee> typedQuery = em.createQuery(criteriaQuery);
typedQuery.getResultList().forEach(System.out::println);
em.close();
}
private static void findEmployeeWithNoTaskSupervisor() {
System.out.println("-- Employees with no task supervisor --");
EntityManager em = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
CriteriaQuery<Employee> criteriaQuery = criteriaBuilder.createQuery(Employee.class);
Root<Employee> employee = criteriaQuery.from(Employee.class);
ListJoin<Employee, Task> tasks = employee.join(Employee_.tasks);
criteriaQuery.select(employee)
.distinct(true)
.where(criteriaBuilder.isNull(tasks.get(Task_.supervisor)));
TypedQuery<Employee> typedQuery = em.createQuery(criteriaQuery);
typedQuery.getResultList().forEach(System.out::println);
em.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);
}
} -- 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 ProjectDependencies and Technologies Used: - h2 1.4.197: H2 Database Engine.
- hibernate-core 5.3.6.Final: Hibernate's core ORM functionality.
Implements javax.persistence:javax.persistence-api version 2.2 - hibernate-jpamodelgen 5.3.6.Final: Annotation Processor to generate JPA 2 static metamodel classes.
- JDK 1.8
- Maven 3.5.4
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