DataNucleus Forum - View Thread - Can't retrieve the 1-to-1 object (null)

bebone
Newbie

France
Joined: Feb 4, 2010
Post Count: 3
Status: Offline


Can't retrieve the 1-to-1 object (null)

Hi,

I try to use Datanucleus to store object with 1-to-1 relation (later i will use 1-to-many relation)
I use the "datanucleus-samples-jdo-tutorial-2.0" project and use the class from the given tutorial http://www.datanucleus.org/products/accessplatform_1_1/jdo/orm/one_to_one.html

As you can see, an account has a 1-to-1 relation to an user.
I create the following classes:


package org.datanucleus.samples.jdo.tutorial;

import javax.jdo.annotations.PersistenceCapable;

@PersistenceCapable
public class Account {

	private Long id;
	private String firstName;
	private String secondName;
	private User user;

	public Account() {
	}

	public Long getId() {
		return id;
	}
	public void setId(Long id) {
		this.id = id;
	}
	public String getFirstName() {
		return firstName;
	}
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
	public String getSecondName() {
		return secondName;
	}
	public void setSecondName(String secondName) {
		this.secondName = secondName;
	}
	public User getUser() {
		return user;
	}
	public void setUser(User user) {
		this.user = user;
	}

}


package org.datanucleus.samples.jdo.tutorial;

import javax.jdo.annotations.PersistenceCapable;

@PersistenceCapable
public class User {

	private Long id;
	private String login;

	public User() {
	}
	
	public Long getId() {
		return id;
	}
	public void setId(Long id) {
		this.id = id;
	}
	public String getLogin() {
		return login;
	}
	public void setLogin(String login) {
		this.login = login;
	}

}

I edit package-hsql.orm with the following code(similar to tutorial website)


<?xml version="1.0"?> 
<!DOCTYPE orm SYSTEM "file:/javax/jdo/orm.dtd"> 
<orm> 
  <package name="org.datanucleus.samples.jdo.tutorial"> 

    <class name="User" identity-type="datastore" table="JDO_USER"> 
      <field name="id" primary-key="true"> 
        <column name="USER_ID" />
      </field> 
      <field name="login"> 
        <column name="LOGIN" length="20" jdbc-type="VARCHAR" /> 
      </field> 
     </class>
     
     <class name="Account" identity-type="datastore" table="JDO_ACCOUNT"> 
        <field name="id" primary-key="true"> 
          <column name="ACCOUNT_ID" /> 
        </field> 
        <field name="firstName"> 
          <column name="FIRSTNAME" length="50" jdbc-type="VARCHAR" /> 
        </field> 
        <field name="secondName"> 
          <column name="SECONDNAME" length="50" jdbc-type="VARCHAR" /> 
        </field> 
        <field name="user" persistence-modifier="persistent"> 
          <column name="USER_ID" /> 
        </field> 
    </class>
 
  </package> 
</orm>

And change the code of the Main.java to do my stuff


...

public class Main {
	public static void main(String args[]) {
		// Create a PersistenceManagerFactory for this datastore
		PersistenceManagerFactory pmf = JDOHelper
				.getPersistenceManagerFactory("datanucleus.properties");

		System.out.println("DataNucleus AccessPlatform with JDO");
		System.out.println("===================================");

		User user = new User();
		user.setId(new Long(1));
		user.setLogin("beb");
		Account account = new Account();
		account.setId(new Long(1));
		account.setFirstName("John");
		account.setSecondName("Doe");
		account.setUser(user);
		
		persistEntity(pmf, account);
		getAllEntity(pmf, Account.class);

                ...

		System.out.println("End of Tutorial");
	}

	private static void persistEntity(PersistenceManagerFactory pmf, Object object) {
		// Persistence of a Product and a Book.
		PersistenceManager pm = pmf.getPersistenceManager();
		Transaction tx = pm.currentTransaction();
		try {
			tx.begin();
			System.out.println("Persisting products");
			pm.makePersistent(object);
			tx.commit();
			System.out.println("Entity have been persisted");
		} finally {
			if (tx.isActive()) {
				tx.rollback();
			}
			pm.close();
		}
		System.out.println("");
	}

	private static void getAllEntity(PersistenceManagerFactory pmf, Class<?> clazz) {
		PersistenceManager pm;
		Transaction tx;
		// Basic Extent of all Products
		pm = pmf.getPersistenceManager();
		tx = pm.currentTransaction();
		try {
			tx.begin();
			System.out.println("Retrieving Extent for '" + clazz.getSimpleName() + "'");
			Extent<?> e = pm.getExtent(clazz, true);
			Iterator<?> iter = e.iterator();
			while (iter.hasNext()) {
				Object obj = iter.next();
				System.out.println(">  " + obj);
			}
			tx.commit();
		} catch (Exception e) {
			System.out.println("Exception thrown during retrieval of Extent : "
					+ e.getMessage());
		} finally {
			if (tx.isActive()) {
				tx.rollback();
			}
			pm.close();
		}
		System.out.println("");
	}

	...

	
}

When i retrieve the object in the getAllEntity() method,
All the attribute of the persisted 'Account' object are well retrieved except the encapsulated 'User' object .
I got a Null pointer...

NB: I use maven plugin defined in the tutorial project to enhance classes and launch the project

Thanks in advance
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[Edit 2 times, last edit by bebone at Feb 4, 2010 12:50:42 PM]

[Feb 4, 2010 12:04:22 PM]

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