JPQL CASE expression is similar to Java 'switch' statement which selects one of the multiple choices based on a provided runtime value. Following is the general syntax of JPQL CASE expression:
CASE property
WHEN property-value-1 THEN scalar-expression-1
WHEN property-value-2 THEN scalar-expression-2
.....
ELSE scalar-expression-n
The 'property' (same or different) can also be used individually within 'WHEN' expression:
CASE
WHEN property=property-value-1 THEN scalar-expression-1
WHEN property=property-value-2 THEN scalar-expression-2
.....
ELSE scalar-expression-n
Example
Entities
@Entity
public class Employee {
@Id
@GeneratedValue
private long id;
private String name;
private double salary;
private String dept;
.............
}
Using CASE expressions
public class ExampleMain {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
persistEmployees();
findAllEmployees();
} finally {
entityManagerFactory.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();
}
private static void findAllEmployees() {
EntityManager em = entityManagerFactory.createEntityManager();
System.out.println("-- All employees --");
Query query = em.createQuery(
"SELECT e.name, e.salary, "
+ "CASE e.dept "
+ "WHEN 'IT' THEN 'Information Technology' "
+ "WHEN 'Admin' THEN 'Administration' "
+ " ELSE e.dept "
+ "END "
+ "FROM Employee e");
List<Object[]> resultList = query.getResultList();
resultList.forEach(o -> System.out.println(Arrays.toString(o)));
em.close();
}
} -- All employees -- [Diana, 2000.0, Information Technology] [Rose, 3500.0, Administration] [Denise, 2500.0, Administration] [Mike, 4000.0, Information Technology] [Linda, 4500.0, Sales]
CASE Expression with polymorphic types
'CASE' can also be used in polymorphic type selection. Check out an example here.
Example ProjectDependencies and Technologies Used: - h2 1.4.197: H2 Database Engine.
- hibernate-core 5.3.1.Final: Hibernate's core ORM functionality.
Implements javax.persistence:javax.persistence-api version 2.2 - JDK 1.8
- Maven 3.5.4
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