Or am i doing something wrong?
I brought this up in an earlier post to which no-one has responded so i took
some time to create a test project. If anyone wants me to zip it up and send,
let me know.
The problem: lazy initialisation of the many part of a OneToMany always returns
an extra record in the array in the form of a null object at the beginning of
the PersistentList.
Variable output
| this= PersistenceManagerBean (id=415)
| id= Integer (id=427)
| a= ClassA (id=435)
| classBs= PersistentList (id=467)
| cachedSize= -1
| directlyAccessible= false
| dirty= false
| initialized= true
| initializing= false
| key= Integer (id=474)
| list= ArrayList<E> (id=481)
| elementData= Object[10] (id=499)
| [0]= null
| [1]= ClassB (id=501)
| [2]= ClassB (id=502)
| [3]= null
| [4]= null
| [5]= null
| [6]= null
| [7]= null
| [8]= null
| [9]= null
| modCount= 3
| size= 3
| operationQueue= null
| owner= ClassA (id=435)
| role= "test.persistence.ClassA.classBs"
| session= SessionImpl (id=488)
| storedSnapshot= ArrayList<E> (id=497)
| id= Integer (id=474)
| name= "main "
| classb= null
|
Persistence Manager
package test.persistence.manager;
|
| //import java.util.List;
|
|
| import javax.ejb.Stateless;
| import javax.persistence.PersistenceContext;
|
| import org.jboss.annotation.ejb.RemoteBinding;
| import test.persistence.ClassA;
| import test.persistence.ClassB;
|
|
|
| @RemoteBinding(jndiBinding="PersistenceManagerTest")
| public @Stateless
| class PersistenceManagerBean implements PersistenceManager {
|
| @PersistenceContext(unitName = "ejb3testproject")
| javax.persistence.EntityManager em;
|
|
|
| public ClassA getClassaById(Integer id) {
|
| ClassA a = new ClassA();
| try {
|
| a = (ClassA) em.createQuery(
| "SELECT DISTINCT OBJECT(a)" + "FROM
ClassA a "
| + "WHERE a.id = :id")
| .setParameter("id", id)
| .getSingleResult();
|
| }
| catch(Exception e)
| {
| System.out.println(e.getLocalizedMessage());
| }
| for(ClassB classb:a.getClassBs())
| {
| System.out.println(classb.getName());
| }
|
| return a;
| }
|
|
| }
|
ClassA Entity
package test.persistence;
| import java.io.Serializable;
| import java.util.List;
|
| import javax.persistence.*;
|
| import org.hibernate.annotations.IndexColumn;
|
| @Entity
| @Table(name="classA")
| public class ClassA implements Serializable{
|
|
| java.lang.String name;
|
| Integer id;
|
| List<ClassB> classBs;
|
|
| @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
| @Column(name="classa_id")
| public java.lang.Integer getId() {
| return id;
| }
|
| public void setId(java.lang.Integer id) {
| this.id = id;
| }
|
| @Column(name="name")
| public java.lang.String getName() {
| return name;
| }
|
| public void setName(java.lang.String name) {
| this.name = name;
| }
|
| @OneToMany(mappedBy="classA")
| @IndexColumn(name="classb_id")
| public List<ClassB> getClassBs() {
| return classBs;
| }
|
| public void setClassBs(List<ClassB> classBs) {
| this.classBs = classBs;
| }
|
| }
|
ClassB Entity
package test.persistence;
| import java.io.Serializable;
| import java.util.List;
|
| import javax.persistence.*;
|
| @Entity
| @Table(name="classB")
| public class ClassB implements Serializable{
|
|
| java.lang.String name;
|
| Integer id;
|
| ClassA classA;
|
|
| @ManyToOne(fetch=FetchType.EAGER)
| @JoinColumn(name="classa_id")
| public ClassA getClassA() {
| return classA;
| }
|
| public void setClassA(ClassA classA) {
| this.classA = classA;
| }
|
| @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
| @Column(name="classb_id")
| public java.lang.Integer getId() {
| return id;
| }
|
| public void setId(java.lang.Integer id) {
| this.id = id;
| }
|
| @Column(name="name")
| public java.lang.String getName() {
| return name;
| }
|
| public void setName(java.lang.String name) {
| this.name = name;
| }
|
| }
|
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