Size of a collection
In Criteria API, the size of a collection can be found by using following methods of CriteriaBuilder:
package javax.persistence.criteria;
........
public interface CriteriaBuilder {
........
<C extends java.util.Collection<?>> Expression<Integer> size(Expression<C> collection);
<C extends Collection<?>> Expression<Integer> size(C collection);
........
}
Index of a collection
Following method of ListJoin create an expression that corresponds to the index of the object in the referenced association or collection.
package javax.persistence.criteria;
........
public interface ListJoin<Z, E> extends PluralJoin<Z, List<E>, E> {
.........
Expression<Integer> index();
}
Example
Entity
@Entity
public class Employee {
@Id
@GeneratedValue
private long id;
private String name;
private double salary;
private String dept;
@ElementCollection
@OrderColumn
private List<String> phoneNumbers;
.............
}
Using size() and index() methods
public class ExampleMain {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
persistEmployees();
findNumberOfPhoneNumbers();
findEmployeeWithMoreThanOnePhoneNumber();
findEmployeeWithMoreThanOnePhoneNumber2();
findPhoneByIndex();
} finally {
entityManagerFactory.close();
}
}
private static void findNumberOfPhoneNumbers() {
System.out.println("-- Find number of phone numbers --");
EntityManager entityManager = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Object[]> query = criteriaBuilder.createQuery(Object[].class);
Root<Employee> employeeRoot = query.from(Employee.class);
query.multiselect(employeeRoot.get(Employee_.id), employeeRoot.get(Employee_.name),
criteriaBuilder.size(employeeRoot.get(Employee_.phoneNumbers.getName())))
.groupBy(employeeRoot.get(Employee_.id), employeeRoot.get(Employee_.name));
//The equivalent JPQL:
//SELECT e.id, e.name, SIZE(e.phoneNumbers) from Employee e GROUP BY e.id, e.name
List<Object[]> resultList = entityManager.createQuery(query).getResultList();
resultList.forEach(o -> System.out.println(Arrays.toString(o)));
entityManager.close();
}
private static void findEmployeeWithMoreThanOnePhoneNumber() {
System.out.println("-- Find employees who have more than 1 phone number by using size() --");
EntityManager entityManager = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Employee> query = criteriaBuilder.createQuery(Employee.class);
Root<Employee> employeeRoot = query.from(Employee.class);
query.select(employeeRoot)
.where(criteriaBuilder.greaterThan(criteriaBuilder.size(employeeRoot.get(Employee_.phoneNumbers)), 1));
//The equivalent JPQL:
//SELECT e from Employee e WHERE SIZE(e.phoneNumbers) > 1
entityManager.createQuery(query)
.getResultList()
.forEach(System.out::println);
}
private static void findEmployeeWithMoreThanOnePhoneNumber2() {
System.out.println("-- Find employees who have more than 1 phone number by using index() --");
EntityManager entityManager = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Employee> query = criteriaBuilder.createQuery(Employee.class);
Root<Employee> employeeRoot = query.from(Employee.class);
ListJoin<Object, Object> phoneNumbersJoin = employeeRoot.joinList(Employee_.phoneNumbers.getName());
query.select(employeeRoot)
.distinct(true)
.where(criteriaBuilder.greaterThan(phoneNumbersJoin.index(), 0));
//The equivalent JPQL:
//SELECT DISTINCT e from Employee e JOIN e.phoneNumbers p WHERE INDEX(p) > 0
entityManager.createQuery(query)
.getResultList()
.forEach(System.out::println);
}
private static void findPhoneByIndex() {
System.out.println("-- Find phones by index in phoneNumbers list --");
EntityManager entityManager = entityManagerFactory.createEntityManager();
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Object[]> query = criteriaBuilder.createQuery(Object[].class);
Root<Employee> employeeRoot = query.from(Employee.class);
ListJoin<Employee, String> phoneNumbersJoin = employeeRoot.joinList(Employee_.phoneNumbers.getName());
query.multiselect(employeeRoot.get(Employee_.name), phoneNumbersJoin.index(), phoneNumbersJoin);
//The equivalent JPQL:
//Select e.name, INDEX(p), p from Employee e JOIN e.phoneNumbers p
List<Object[]> resultList = entityManager.createQuery(query).getResultList();
resultList.forEach(o -> System.out.println(Arrays.toString(o)));
entityManager.close();
}
public static void persistEmployees() {
Employee employee1 = Employee.create("Diana", 2000, "IT", "111-111-111", "666-666-666", "777-777-777");
Employee employee2 = Employee.create("Rose", 3500, "Admin", "222-222,222", "888-888-888");
Employee employee3 = Employee.create("Denise", 2500, "Admin", "333-333-333");
Employee employee4 = Employee.create("Mike", 4000, "IT", "444-444-444");
Employee employee5 = Employee.create("Linda", 4500, "Sales", "555-555-555");
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("-- Employees persisted --");
Query query = em.createQuery(
"SELECT e FROM Employee e");
List<Employee> resultList = query.getResultList();
resultList.forEach(System.out::println);
em.close();
}
}-- Employees persisted --
Employee{id=1, name='Diana', salary=2000.0, dept='IT', phoneNumbers=[111-111-111, 666-666-666, 777-777-777]}
Employee{id=2, name='Rose', salary=3500.0, dept='Admin', phoneNumbers=[222-222,222, 888-888-888]}
Employee{id=3, name='Denise', salary=2500.0, dept='Admin', phoneNumbers=[333-333-333]}
Employee{id=4, name='Mike', salary=4000.0, dept='IT', phoneNumbers=[444-444-444]}
Employee{id=5, name='Linda', salary=4500.0, dept='Sales', phoneNumbers=[555-555-555]}
-- Find number of phone numbers --
[1, Diana, 3]
[2, Rose, 2]
[3, Denise, 1]
[4, Mike, 1]
[5, Linda, 1]
-- Find employees who have more than 1 phone number by using size() --
Employee{id=1, name='Diana', salary=2000.0, dept='IT', phoneNumbers={IndirectList: not instantiated}}
Employee{id=2, name='Rose', salary=3500.0, dept='Admin', phoneNumbers={IndirectList: not instantiated}}
Employee{id=3, name='Denise', salary=2500.0, dept='Admin', phoneNumbers={IndirectList: not instantiated}}
Employee{id=4, name='Mike', salary=4000.0, dept='IT', phoneNumbers={IndirectList: not instantiated}}
Employee{id=5, name='Linda', salary=4500.0, dept='Sales', phoneNumbers={IndirectList: not instantiated}}
-- Find employees who have more than 1 phone number by using index() --
Employee{id=1, name='Diana', salary=2000.0, dept='IT', phoneNumbers={IndirectList: not instantiated}}
Employee{id=2, name='Rose', salary=3500.0, dept='Admin', phoneNumbers={IndirectList: not instantiated}}
-- Find phones by index in phoneNumbers list --
[Rose, 0, 222-222,222]
[Rose, 1, 888-888-888]
[Linda, 0, 555-555-555]
[Mike, 0, 444-444-444]
[Denise, 0, 333-333-333]
[Diana, 0, 111-111-111]
[Diana, 1, 666-666-666]
[Diana, 2, 777-777-777]
Example ProjectDependencies and Technologies Used: - eclipselink 2.6.5: EclipseLink build based upon Git transaction b3d05bd.
Related JPA version: org.eclipse.persistence:javax.persistence version 2.1.1 - org.eclipse.persistence.jpa.modelgen.processor 2.6.5: EclipseLink build based upon Git transaction b3d05bd.
- h2 1.4.198: H2 Database Engine.
- JDK 1.8
- Maven 3.5.4
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