Named queries are reusable static queries that we create and associate with an entity. At runtime, we can use the EntityManager to acquire, configure, and execute a named query.
Named queries can be created using annotation javax.persistence.NamedQuery which specifies the name of the query and query (in JPQL) itself.
During runtime we can use EntityManager#createNamedQuery() method to access them.
Example
Entities
@Entity
@NamedQuery(name = Employee.SALARY_RANGE_QUERY,
query = "SELECT e FROM Employee e WHERE e.salary BETWEEN :min AND :max order by e.salary")
@NamedQuery(name = Employee.SALARY_LESS_THAN_AVERAGE_QUERY,
query = "SELECT e FROM Employee e where e.salary < (SELECT AVG(e2.salary) FROM Employee e2)")
public class Employee {
public static final String SALARY_RANGE_QUERY = "salaryRangeQuery";
public static final String SALARY_LESS_THAN_AVERAGE_QUERY = "salaryLessThanAverageQuery";
@Id
@GeneratedValue
private long id;
private String name;
private Timestamp joinDate;
private long salary;
.............
}
As @NameQuery is a repeatable annotation, we can use multiple of them on entity classes.
Executing named queries
public class ExampleMain {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
persistEmployees();
findEmployeeBySalaryRange();
findEmployeeWithLessThanAverageSalary();
} finally {
entityManagerFactory.close();
}
}
private static void findEmployeeBySalaryRange() {
System.out.println("-- Employee by salary range --");
EntityManager em = entityManagerFactory.createEntityManager();
Query query = em.createNamedQuery(Employee.SALARY_RANGE_QUERY);
query.setParameter("min", 2000L);
query.setParameter("max", 4000L);
List<Employee> resultList = query.getResultList();
resultList.forEach(System.out::println);
em.close();
}
private static void findEmployeeWithLessThanAverageSalary() {
System.out.println("-- Employee with salary less than average --");
EntityManager em = entityManagerFactory.createEntityManager();
Query query = em.createNamedQuery(Employee.SALARY_LESS_THAN_AVERAGE_QUERY);
List<Employee> resultList = query.getResultList();
resultList.forEach(System.out::println);
em.close();
}
public static void persistEmployees() {
Employee employee1 = Employee.create("Diana", 3000, LocalDate.of(1999, 11, 15));
Employee employee2 = Employee.create("Rose", 4000, LocalDate.of(2011, 5, 1));
Employee employee3 = Employee.create("Denise", 1500, LocalDate.of(2006, 1, 10));
Employee employee4 = Employee.create("Mike", 2000, LocalDate.of(2015, 8, 20));
EntityManager em = entityManagerFactory.createEntityManager();
em.getTransaction().begin();
em.persist(employee1);
em.persist(employee2);
em.persist(employee3);
em.persist(employee4);
em.getTransaction().commit();
em.close();
}
private static Timestamp localToTimeStamp(LocalDate date) {
return Timestamp.from(date.atStartOfDay().toInstant(ZoneOffset.UTC));
}
} -- Employee by salary range -- Employee{id=4, name='Mike', joinDate=2015-08-19 19:00:00.0, salary=2000} Employee{id=1, name='Diana', joinDate=1999-11-14 18:00:00.0, salary=3000} Employee{id=2, name='Rose', joinDate=2011-04-30 19:00:00.0, salary=4000} -- Employee with salary less than average -- Employee{id=3, name='Denise', joinDate=2006-01-09 18:00:00.0, salary=1500} Employee{id=4, name='Mike', joinDate=2015-08-19 19:00:00.0, salary=2000}
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 3.3.9
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