How to retrieve detached @ManyToOne entities with Fetch Join relationship

[Jack Bush]

Hi All,

I am having difficulty retrieving all the Zipcode, Zipname records which have successfully been deployed on Glassfish v2r2, JDK1.6.0_06, MySQL 5.0, Netbeans 6.1 on Windows XP platform. Below are the relevant EJBs snippets:

package domain;
@Entity
@Table(name="ZIPCODE")
public class Zipcode implements Serializable {

@Id
@Column(name="ID")
private int id;
public int getId() {
return id;
}
.....
@OneToMany(cascade={CascadeType.ALL}, mappedBy="zipcode", fetch=FetchType.EAGER, targetEntity=Zipname.class)
private Collection<Zipname> zipnames = new ArrayList<Zipname>();
public Collection<Zipname> getNames() {
return zipnames;
}
.....

package domain;
@Entity
@Table(name="ZIPNAME")
public class Zipname implements Serializable {
@Id
@Column(name="ID")
private int id;
public void setId(int id) {
this.id = id;
}
.....

@ManyToOne(fetch=FetchType.EAGER)
@JoinColumn(name="ZIPCODE_ID")
private Zipcode zipcode;
public Zipcode getZipcode() {
return zipcode;
}
......

package ejb;
@Stateless
public class ZipcodeBean implements ZipcodeRemote {

@PersistenceContext(unitName="GeographicalDB") private EntityManager manager;

public void createZipcode(Zipcode zipcode) {
manager.persist(zipcode);
}

public Zipcode findZipcode(int pKey) {
Zipcode zipcode = manager.find(Zipcode.class, pKey);
zipcode.getNames().size();
return zipcode;
}


public List fetchZipcodesWithRelationships() {
List list = manager.createQuery("SELECT zc FROM Zipcode zc LEFT JOIN FETCH zc.zipnames").getResultList();
for (Object obj : list) {
Zipcode zipcode = (Zipcode)obj;
zipcode.getNames().size();
}
return list;
}

@Stateless
public class ZipnameBean implements ZipnameRemote {

@PersistenceContext(unitName="GeographicalDB") private EntityManager manager;

public void createZipname(Zipname zipname) {
manager.persist(zipname);
}

public Zipname findZipname(int pKey) {
Zipname zipname = manager.find(Zipname.class, pKey);
zipname.getZipcode().getNames().size();
return zipname;
}


public List fetchZipnamesWithRelationships() {
List list = manager.createQuery("FROM Zipname zipname").getResultList();
for (Object obj : list) {
Zipname zipname = (Zipname)obj;
zipname.getZipcode().getNames().size();
}
return list;
}

public class ZipcodeApplicationClient {
@EJB
private static ZipcodeRemote zipcodebean;
private static ZipnameRemote zipnamebean;


public static void main(String[] args) {
try {
Zipcode zipcode_1 = new Zipcode();
zipcode_1.setcode(9001);
Zipname zipname_1 = new Zipname();
zipname_1.setName("Harbour Cove");
zipcode_1.getNames().add(zipname_1);
.......
zipname_1.setZipcode(zipcode_1);
// zipnamebean.createZipname(zipname_1);
zipcodebean.createZipcode(zipcode_1);
-----------------------------------------------------------------
//fetch detached entity without relationship
Zipcode zipcode_2 = zipcodebean.findZipcode(0);
System.out.println("zipcode_2.getId(): " + zipcode_2.getId());
System.out.println("zipcode_2.getCode(): " + zipcode_2.getCode());
Iterator iterator = zipcode_2.getNames().iterator();
while (iterator.hasNext())
{
System.out.println(iterator.next().toString());
}
-----------------------------------------------------------------
// output of fetching detached entity without relationship
zipcode_2.getId(): 0
zipcode_2.getCode(): 2010
domain.ZipName@107e9a8 ([email]domain.ZipName@107e9a8[/email])
-----------------------------------------------------------------
//fetch detached entity with relationship
List list = zipcodebean.fetchZipcodesWithRelationships();
-----------------------------------------------------------------
// output of fetching detached entity with relationship
-----------------------------------------------------------------------------------------------------------------------------------
//fetch detached entity with relationship
List list = zipcodebean.fetchZipcodesWithRelationships();//line 76
for (Object obj : list) {
Zipcode zipcode_2 = (Zipcode)obj;
System.out.println("zipcode_2.getId(): " + zipcode_2.getId());
System.out.println("zipcode_2..getCode(): " + zipcode_2.getCode());
System.out.println("\tNumber of names: " + zipcode_2.getNames().size());
Iterator iterator = zipcode_2.getNames().iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next().toString());
}
}
------------------------------------------------------------------
// output of fetching detached entity with relationship
------------------------------------------------------------------
zipcode_2.getId(): 0
zipcode_2.getCode(): 9001
Number of names: 1
domain.Zipname@8bf3ec ([email]domain.Zipname@8bf3ec[/email])
-------------------------------------------------------

( i ) As a result, please advice on how to utilise both fetchZipcodesWithRelationships() & fetchZipnamesWithRelationships() in ZipcodeApplicationClient() to retrieve collections of Zipcodes & Zipnames correctly?
(ii) I like to utilise the zipnamebean.createZipnamez(zipname_1) to properly create this entity.
(iii) I don't understand why the FETCH JOIN Query is necessary when both entity were setup with FetchType.EAGER?

I have tried various approaches and googled without success.

This question has been posted on http://forums.sun.com/thread..jspa?threadID=5330670&tstart=0 and http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=78&t=004489&p=1 earlier in the hope of a quicker response.
Your guidances would be very much appreciated.
Many thanks,
Jack



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