Why entityManager.contains returns different results? - jpa

Question

This is in JPA2 (EclipseLink) and JSF2.
I have an entity class Student:
#Entity
public class Student implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String firstname;
private String lastname;
private int age;
public Student(String firstname, String lastname, int age) {
this.firstname = firstname;
this.lastname = lastname;
this.age = age;
}
public Student() {
}
// accessors and mutators here
}
Session bean StudentFacade that inherits AbstractFacade:
public abstract class AbstractFacade<T> {
private Class<T> entityClass;
public AbstractFacade(Class<T> entityClass) {
this.entityClass = entityClass;
}
protected abstract EntityManager getEntityManager();
public void create(T entity) {
getEntityManager().persist(entity);
}
public T edit(T entity) {
return getEntityManager().merge(entity);
}
public void remove(T entity) {
getEntityManager().remove(getEntityManager().merge(entity));
}
public T find(Object id) {
return getEntityManager().find(entityClass, id);
}
// other methods: findAll, findRange, count
}
#Stateless
public class StudentFacade extends AbstractFacade<Student> {
#PersistenceContext(unitName = "jpa2testsPU")
private EntityManager em;
#Override
protected EntityManager getEntityManager() {
return em;
}
public StudentFacade() {
super(Student.class);
}
public boolean contains(Student s) {
return getEntityManager().contains(s);
}
public void testContains() {
Student s = find(1L);
boolean isContains = getEntityManager().contains(s);
}
}
This is my JSF Managed Bean:
#ManagedBean
#RequestScoped
public class IndexController {
#EJB
private StudentFacade studentFacade;
/**
* Creates a new instance of IndexController
*/
public IndexController() {
}
public String test() {
Student s = new Student("John", "Doe", 20);
studentFacade.create(s);
Student s1 = studentFacade.find(1L); // This works because table only has 1 record
boolean isContains = studentFacade.contains(s);
return null;
}
}
When I run test() from managed bean, isContains is false. But when testContains() in StudentFacade is called, isContains is true. Why is this?

Answer 1

StudentFacade is a Stateless Session Bean (SSB). The contents of its instance variables are not guaranteed to be preserved across method calls (reference). It's like having a different instance of EntityManager created for each method invocation.
When you run your test from the managed bean, you invoke two different methods on the SSB, therefore a different EntityManager instance is created for each call, and the second one does not contain the Student instance because it has not been loaded yet.
But when you run your test inside a method of the SSB itself, the same EntityManager is used for the scope of the entire method, therefore the call to contains() returns true.