Java(TM) Boutique - Mapping Java Objects to a Database with Castor-JDO

Reviews :

Mapping Java Objects to a Database with Castor-JDO:

Here's a program that creates three actors and add them to the movies:

package hansen.playground;
import org.exolab.castor.jdo.*;
import java.util.*;

public class CreateActors {
  public static void main(String[] args) {
    try {
      // Define the JDO object
      JDO jdo = new JDO("mydb"); 
      jdo.setConfiguration("database.xml"); 

      // Open a connection to the database
      Database db = jdo.getDatabase();
      
      // Begin a transaction
      db.begin(); 
      
      OQLQuery query; 
      QueryResults results; 
      query = db.getOQLQuery(
        "SELECT a FROM hansen.playground.Movie a WHERE a.id=11");
      results = query.execute();
      Movie Matrix = (Movie)results.next();

      query = db.getOQLQuery(
        "SELECT a FROM hansen.playground.Movie a WHERE a.id=12");
      results = query.execute();
      Movie Rings = (Movie)results.next();

      query = db.getOQLQuery(
        "SELECT a FROM hansen.playground.Movie a WHERE a.id=13");
      results = query.execute();
      Movie Chain = (Movie)results.next();

      Actor a1 = new Actor(21, "Keanu Reeves");
      a1.addMovie(Matrix);
      a1.addMovie(Chain);
      db.create(a1);
      Matrix.addActor(a1);

      Actor a2 = new Actor(22, "Laurence Fishburne");
      a2.addMovie(Matrix);
      db.create(a2);
      Matrix.addActor(a2);

      Actor a3 = new Actor(23, "Ian Holm");
      a3.addMovie(Rings);
      db.create(a3);
      Rings.addActor(a3);

      // Commit the transaction
      db.commit(); 
      db.close(); 

    } catch (PersistenceException e) {
      e.printStackTrace(); 
    }  
  }
}

- Listing 7: Testprogram for the Actor class -

Note, that I've used an alternate way of loading the objects, using OQL, the Object Query Language. OQL looks a lot like SQL, but uses Java class names in stead of table names.

The actor table now contains

id	name
21	Keanu Reeves
22	Laurence Fishburne
23	Ian Holm

The actor_movie table contains:

id_actor	id_movie
21	11
21	13
22	11
23	12

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