ObjectDB supports user defined methods in queries.
The following example demonstrates using this ability to retrieve cities in a specific radius from Paris:
import java.util.List;
import javax.persistence.*;
public class T1794 {
public static void main(String[] args) {
EntityManagerFactory emf =
Persistence.createEntityManagerFactory(
"objectdb:$objectdb/db/points2.tmp;drop");
EntityManager em = emf.createEntityManager();
em.getTransaction().begin();
em.persist(new Location("London", 51.507351, -0.127758));
em.persist(new Location("Paris", 48.856614, 2.352222));
em.persist(new Location("Berlin", 52.520007, 13.404954));
em.persist(new Location("New York", 40.712784, -74.005941));
em.persist(new Location("Tokio", 35.689487, 139.691706));
em.persist(new Location("Sydney", -33.867487, 151.206990));
em.getTransaction().commit();
findNearby(em, "Paris", 500);
findNearby(em, "Paris", 1000);
findNearby(em, "Paris", 6000);
findNearby(em, "Paris", 10000);
em.close();
emf.close();
}
private static void findNearby(
EntityManager em, String locationName, int radius) {
Location location = em.find(Location.class, locationName);
TypedQuery<Location> query = em.createQuery(
"SELECT l FROM Location l " +
"WHERE l.distance((double):latitude, (double):longitude) < :radius",
Location.class);
List<Location> resultList = query
.setParameter("latitude", location.getLatitude())
.setParameter("longitude", location.getLongitude())
.setParameter("radius", radius)
.getResultList();
System.out.println(radius + "km From " + location + ": "+ resultList);
}
@Entity
public static class Location {
@Id private String name;
private double latitude;
private double longitude;
public String getName() { return name; }
public double getLatitude() { return latitude; }
public double getLongitude() { return longitude; }
public Location(String name, double latitude, double longitude) {
this.name = name;
this.latitude = latitude;
this.longitude = longitude;
}
public double distance(double toLatitude, double toLongitude) {
double cx = Math.toRadians(latitude);
double cy = Math.toRadians(longitude);
double px = Math.toRadians(toLatitude);
double py = Math.toRadians(toLongitude);
double gamma = Math.acos(Math.sin(cx) * Math.sin(px) +
Math.cos(cx) * Math.cos(px) * Math.cos(py - cy));
return gamma * 6370.0;
}
@Override
public String toString() {
return name;
}
}
} Note: In client server mode you must make your entity class (with the method that is used in the query) available to the server by running the ObjectDB Server with a classpath that includes your entity classes.
