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hibernate and mappedBy: Is it possible to automatically set foreign key without setting bidirectional relationship among objects?

Welcome,
I have 2 classes: Conversation and Question. One Conversation have many questions.
Conversation.java:
package com.jcg.jpa.mappedBy;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
#Entity
#Table(name = "CONVERSATION_TABLE")
public class Conversation implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#Column(name = "CONV_ID")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int conversationId;
#Column(name = "CONV_NAME")
private String name;
#OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy="conversation")
private Collection<Question> questions = new ArrayList<Question>();
public Conversation() { }
public int getConversationId() {
return conversationId;
}
public void setConversationId(int conversationId) {
this.conversationId = conversationId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Collection<Question> getQuestions() {
return questions;
}
public void setQuestions(Collection<Question> questions) {
this.questions = questions;
}
#Override
public String toString() {
return "Employee [conversationId=" + conversationId + ", name=" + name + "]";
}
}
Question.java:
package com.jcg.jpa.mappedBy;
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
#Entity
#Table(name = "QUESTION_TABLE")
public class Question implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#Column(name = "id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
#ManyToOne
#JoinColumn(name = "CONVERSATION_CONV_ID", nullable = false)
private Conversation conversation;
#Column(name = "QUESTION_TEXT")
private String questionText;
#Column(name = "ANSWER_TEXT")
private String answerText;
public Question() { }
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getQuestionText() {
return questionText;
}
public void setQuestionText(String questionText) {
this.questionText = questionText;
}
public String getAnswerText() {
return answerText;
}
public void setAnswerText(String answerText) {
this.answerText = answerText;
}
public Conversation getConversation() {
return conversation;
}
public void setConversation(Conversation conversation) {
this.conversation = conversation;
}
#Override
public String toString() {
return "Question [id=" + id + ", questionText=" + questionText
+ ", answerText=" + answerText +"]";
}
}
persistence.xml:
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1"
xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="JPAMappedbyExample" transaction-type="RESOURCE_LOCAL">
<class>com.jcg.jpa.mappedBy.Conversation</class>
<class>com.jcg.jpa.mappedBy.Question</class>
<!-- Configuring The Database Connection Details -->
<properties>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/jpatest" />
<property name="javax.persistence.jdbc.user" value="root" />
<property name="javax.persistence.jdbc.password" value="qwerty" />
</properties>
</persistence-unit>
And now in Main.java I'm trying to create Conversation with two questions:
package com.jcg.jpa.mappedBy;
import java.util.ArrayList;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public class Main {
private static final EntityManagerFactory emFactoryObj;
private static final String PERSISTENCE_UNIT_NAME = "JPAMappedbyExample";
static {
emFactoryObj = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
}
// This Method Is Used To Retrieve The 'EntityManager' Object
public static EntityManager getEntityManager() {
return emFactoryObj.createEntityManager();
}
private static void insertRecords() {
EntityManager entityMgrObj = getEntityManager();
if (null != entityMgrObj) {
entityMgrObj.getTransaction().begin();
Conversation conv = new Conversation();
conv.setName("Discussion about something");
Question question1 = new Question();
question1.setQuestionText("2 plus 2");
question1.setAnswerText("four");
question1.setConversation(conv);
Question question2 = new Question();
question2.setQuestionText("what is Your name");
question2.setAnswerText("Adam");
question2.setConversation(conv);
List<Question> questions = new ArrayList<Question>();
questions.add(question1);
questions.add(question2);
conv.setQuestions(questions);
entityMgrObj.persist(conv);
entityMgrObj.getTransaction().commit();
entityMgrObj.clear();
System.out.println("Record Successfully Inserted In The Database");
}
}
public static void main(String[] args) {
insertRecords();
}
}
In insertRecords() I'm creating conv and two questions.
each of questions has set conversation:
question1.setConversation(conv);
question2.setConversation(conv);
Next, a question list which contains these 2 questions is created
and set to conv questions list:
conv.setQuestions(questions);
An it is working ok, because data is inserted into both tables,
and foreign key CONVERSATION_CONV_ID is filled:
However when I remove setting conversation in questions, lines:
question1.setConversation(conv);
question2.setConversation(conv);
foreign key is set to NULL. Why? We already added two questions to conversation questions list:
#OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy="conversation")
private Collection<Question> questions = new ArrayList<Question>();
, so hibernate should know what is conversation foreign key for these two questions (because they are located on specified conversation questions list). So is it possible to avoid setting Conversation for each of the questions and only add questions to Conversation's question list ? How should I configure entities to do that? Or maybe it's impossible and we always need to set it both directions?

so hibernate should know what is conversation foreign key for these two questions (because they are located on specified conversation questions list).
No Hibernate shouldn't know what is the Conversation of these two Questions if you don't specify it using setConversation(), because it's dealing with objects here, and these two questions doesn't have any indication on which Conversation they are part of.
Explanation:
Because when you only add these two questions to the Conversation object, this information won't be visible in the Questions objects.
Another thing here, the mappedBy attribute is indicating wich object is the owner of the mapping, so how can the mapping be made if there's no given object in the mappedBy side?
That's why you should specify the Conversation in Question object, so the mapping can be correctly evaluated by Hibernate.
Note:
It's recommended to use a Set for OneToMany mapping rather than any other Collection, because this collection shouldn't have any duplicates, so you better change it to:
#OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy="conversation")
private Set<Question> questions = new HashSet<Question>();

save working but persist not working in hibernate 4.1.1

I am trying to save data usign hsqldb and I am using hibernate 4.1.4.Final. My problem is I want to save data using persist but when I tried to do it's showing following error:
org.hibernate.PersistentObjectException: detached entity passed to persist: main.java.entity.Advocate
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:141)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:835)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:828)
at org.hibernate.engine.spi.CascadingAction$7.cascade(CascadingAction.java:315)
at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:380)
at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:165)
at org.hibernate.event.internal.AbstractSaveEventListener.cascadeBeforeSave(AbstractSaveEventListener.java:423)
at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:264)
at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:193)
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:126)
at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:208)
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:151)
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:78)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:844)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:819)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:823)
at main.java.service.LegalService.registerCase(LegalService.java:46)
at main.java.tester.Tester.registerCase(Tester.java:52)
at main.java.tester.Tester.main(Tester.java:28)
But when I use save method it worked.So I want to know how persist and save makes difference? and my entity classes are serialized.How to solve this persist error.
Here is my class
package main.java.service;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import main.java.businessTier.CaseTO;
import main.java.entity.Advocate;
import main.java.entity.Case;
public class LegalService {
Configuration configuration = new Configuration().configure();
ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(
configuration.getProperties()). buildServiceRegistry();
SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
public int registerCase(CaseTO caseTO) {
try
{
Session session;
session=sessionFactory.openSession();
session.beginTransaction();
Case c = new Case();
Advocate a = new Advocate();
a.setAdvocateId(caseTO.getAdvocateId());
c.setAdvocate(a);
c.setClientAge(caseTO.getClientAge());
c.setClientName(caseTO.getClientName());
c.setDate(caseTO.getDate());
c.setDescription(caseTO.getDescription());
session.persist(c);
session.getTransaction().commit();
return c.getCaseNo();
}
catch(Exception e){
e.printStackTrace();
return 0;
}
}
}
Here are my entity class
Advocate.java
package main.java.entity;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
import org.hibernate.annotations.DynamicInsert;
import org.hibernate.annotations.DynamicUpdate;
#Entity
#Table(name="Db_Advocate")
#DynamicInsert(value=true)
#DynamicUpdate(value=true)
public class Advocate {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
#Column(name="advocateId")
private Integer advocateId;
#Column(name="name")
private String name;
#Column(name="age")
private Integer age;
#Column(name="category")
private String category;
#Column(name="court")
private String court;
#Column(name="city")
private String city;
public Integer getAdvocateId() {
return advocateId;
}
public void setAdvocateId(Integer advocateId) {
this.advocateId = advocateId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getCategory() {
return category;
}
public void setCategory(String category) {
this.category = category;
}
public String getCourt() {
return court;
}
public void setCourt(String court) {
this.court = court;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
}
Case.java
package main.java.entity;
import java.util.Date;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import org.hibernate.annotations.DynamicInsert;
import org.hibernate.annotations.DynamicUpdate;
#Entity
#Table(name="DB_CASE")
#DynamicInsert(value=true)
#DynamicUpdate(value=true)
public class Case {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private Integer caseNo;
#JoinColumn(name="advocateId")
#ManyToOne(cascade=CascadeType.ALL)
private Advocate advocate;
private String clientName;
private Integer clientAge;
private String description;
private Date date;
public Integer getCaseNo() {
return caseNo;
}
#Column(name="caseNo")
public void setCaseNo(Integer caseNo) {
this.caseNo = caseNo;
}
public Advocate getAdvocate() {
return advocate;
}
public void setAdvocate(Advocate advocateId) {
this.advocate = advocateId;
}
public String getClientName() {
return clientName;
}
public void setClientName(String clientName) {
this.clientName = clientName;
}
public Integer getClientAge() {
return clientAge;
}
public void setClientAge(Integer clientAge) {
this.clientAge = clientAge;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public Date getDate() {
return date;
}
#Column(name="data",nullable=true)
public void setDate(Date date) {
this.date = date;
}
}

First you need to understand behaviour of persist().
Below are the links that will help you understand the behaviour
Whats the difference between persist() and save() in Hibernate?
http://javarevisited.blogspot.in/2012/09/difference-hibernate-save-vs-persist-and-saveOrUpdate.html
Now in order to solve this problem in your code .. use merge() instead of persist().
Why persist() gave the exception
persist() does not work for detached objects .You need to know how hibernate determines whether an object is detached or not.
UPDATE
Why the identifier generation strategy auto solved your problem
As i mentioned above that you need to understand the rules by which hibernate identifies whether an object is detached or transient. Below are the rule
If the the entity has a null value for identifier or the version attribute is null it is considered as transient other wise detached.
If you use auto-generated identifiers, and the identifier is not null, then Hibernate considers it as a detached entity.
If you are using assigned identifier strategy then hibernate will issue a fetch to determine whether the identifier exists in db based on that your entity will be either transient or detached.
Now that being said .. we analyse your code.
In your code you have Advocate entity whose identifier strategy is IDENTITY.In the below code
Case c = new Case();
Advocate a = new Advocate();
a.setAdvocateId(caseTO.getAdvocateId());
You are setting the identifier property of Advocate instance manually.At the time of flush when transaction commits ,hibernate will see that the identifier generation strategy is IDENTITY and the identifier value is set in the advocate instance hence it will conclude that the entity instance is detached (this is from the rule 1 described above).And hence the persist() method gave exception for the advocate instance as it is deemed to be detached from hibernate.
From rule 2 we can say that your code will not work just by changing the generation strategy to auto.You might have done some other changes.
I have tried your code on my system it is giving the same exception even if i change the generation strategy to auto which is in consistent with the rules
You might be doing something different in your code .. please check and update.
Please also post the identifier that you are setting in the advocate and the actual identifier generated for that advocate in database with auto generation strategy, that might be helpful

Please Add below code at id
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
Then persist will work

retrieve data of collection type from database using getters and setters

i am having three classes one is USER, second Vehicle and third is notfound_test.
In USER class i declared vehicle as Collection as follow.
Collection vehicle=new ArrayList();
And also having getters and setters of it.
So, my question is how i can retrieve data from database i am using hibernate?
I tried following code.
i am unable from getting data in JOPTIONPANE OF VEHICLE IN THIRD CLASS.i wanted the associated data
package org.notfound.annotation;
import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
#Entity
public class User {
#Id #GeneratedValue
private int id;
private String name;
#OneToMany
Collection<Vehicle> vehicle=new ArrayList<Vehicle>();
public Collection<Vehicle> getVehicle() {
return vehicle;
}
public void setVehicle(Collection<Vehicle> vehicle) {
this.vehicle = vehicle;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
package org.notfound.annotation;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
#Entity
public class Vehicle {
#Id #GeneratedValue
private int vehicle_id;
private String vehicle_name;
#ManyToOne
private User user=new User();
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public int getVehicle_id() {
return vehicle_id;
}
public void setVehicle_id(int vehicle_id) {
this.vehicle_id = vehicle_id;
}
public String getVehicle_name() {
return vehicle_name;
}
public void setVehicle_name(String vehicle_name) {
this.vehicle_name = vehicle_name;
}
}
package org.notfound.annotation;
import javax.swing.JOptionPane;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class Notfound_test {
public static void main(String[] args) {
User user=new User();
Vehicle vehicle=new Vehicle();
Vehicle vehicle2=new Vehicle();
user.setName("NIRAV J. KAMANI");
vehicle.setVehicle_name("CHEVROLET CRUIZE");
vehicle2.setVehicle_name("MARUTI ERTIGA");
vehicle.setUser(user);
vehicle2.setUser(user);
user.getVehicle().add(vehicle);
user.getVehicle().add(vehicle2);
SessionFactory sessionfactory=new Configuration().configure().buildSessionFactory();
Session session=sessionfactory.openSession();
/*session.beginTransaction();
session.save(user);
session.save(vehicle);
session.save(vehicle2);
session.getTransaction().commit();
session.close();*/
session.beginTransaction();
user=(User) session.get(User.class, 1);
vehicle=(Vehicle) session.get(Vehicle.class, 1);
vehicle2=(Vehicle) session.get(Vehicle.class, 2);
JOptionPane.showMessageDialog(null, user.getId()+" "+user.getName()+" "+user.getVehicle().toString(), "INFORMATION", JOptionPane.INFORMATION_MESSAGE);
session.close();
}
}

As always, you forgot the mappedBy annotation on the OneToMany. It's a bidirectional OneToMany association, and the one side must thus be the inverse side of the many side, as explained in the documentation:
#OneToMany(mappedBy = "user")
private Collection<Vehicle> vehicles = new ArrayList<Vehicle>();
I also renamed the fields to vehicles, since it's a collection, and thus contains several ones.
EDIT:
Your comment shows that the 2 vehicles are printed:
[org.notfound.annotation.Vehicle#37ed25, org.notfound.annotation.Vehicle#aec63]
^-- first vehicle ^-- second vehicle
^-- brackets, indicating that it's a collection ------------------------------^
If you want them to be printed is a different way than the dafult way, you need to override the toString() method in vehicle, as for any Java object.

How to avoid LazyInitializationException in Hibernate?

I am using Hibernate as the ORM for a database that has a number of foreign key relationships. The problem is that sometimes I want to fetch these related datasets and sometimes I do not, so on these collections I have set "fetch" to "lazy". Unfortunately, every time I try to serialize these objects Hibernate will throw a LazyInitializationException, because the session is closed. Using an OpenSessionInView filter simply causes Hibernate to populate these collections anyway, thus defeating the whole purpose of having a lazy collection in the first place.
Is there a simple way to serialize or otherwise extract the data populated in the POJO without triggering the LIE, and without having to populate all of the lazy collections?
EDIT: Here is some example code I am trying to get working, dealing with two tables, "Departments" and "Employees," which is the child in a one-to-many relationship with Departments. I want to be able to view the Departments listed in the database, without having to load all of the Employees that belong to said Departments:
Departments:
package com.test.model;
// Generated Apr 7, 2012 7:10:28 PM by Hibernate Tools 3.4.0.CR1
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
/**
* Departments generated by hbm2java
*/
#Entity
#Table(name="Departments"
,catalog="test"
)
public class Departments implements java.io.Serializable {
private Integer id;
private String name;
private Set<Employees> employeeses = new HashSet(0);
public Departments() {
}
public Departments(String name) {
this.name = name;
}
public Departments(String name, Set employeeses) {
this.name = name;
this.employeeses = employeeses;
}
#Id #GeneratedValue(strategy=IDENTITY)
#Column(name="Id", unique=true, nullable=false)
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
#Column(name="Name", nullable=false)
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
#OneToMany(fetch=FetchType.LAZY, mappedBy="departments")
public Set<Employees> getEmployeeses() {
return this.employeeses;
}
public void setEmployeeses(Set employeeses) {
this.employeeses = employeeses;
}
}
Employees:
package com.test.model;
// Generated Apr 7, 2012 7:10:28 PM by Hibernate Tools 3.4.0.CR1
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
/**
* Employees generated by hbm2java
*/
#Entity
#Table(name="Employees"
,catalog="test"
)
public class Employees implements java.io.Serializable {
private Integer id;
private Departments departments;
private String firstName;
private String lastName;
public Employees() {
}
public Employees(Departments departments, String firstName, String lastName) {
this.departments = departments;
this.firstName = firstName;
this.lastName = lastName;
}
#Id #GeneratedValue(strategy=IDENTITY)
#Column(name="Id", unique=true, nullable=false)
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name="DepartmentsId", nullable=false)
public Departments getDepartments() {
return this.departments;
}
public void setDepartments(Departments departments) {
this.departments = departments;
}
#Column(name="FirstName", nullable=false)
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
#Column(name="LastName", nullable=false)
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
My action class (which gets serialized by the Struts2 XSLT result):
package com.test.view;
import java.util.List;
import java.util.Iterator;
import com.opensymphony.xwork2.ActionSupport;
import com.test.controller.DepartmentsManager;
import com.test.model.Departments;
import com.test.util.HibernateUtil;
public class DepartmentsAction extends ActionSupport {
private DepartmentsManager departmentsManager;
private List<Departments> departmentsList;
public DepartmentsAction() {
this.departmentsManager = new DepartmentsManager();
}
public String list() {
this.departmentsList = departmentsManager.list();
System.out.println("Execute called");
HibernateUtil.createDTO(departmentsList);
return SUCCESS;
}
public List<Departments> getDepartmentsList() {
return departmentsList;
}
public void setDepartmentsList(List<Departments> departmentsList) {
this.departmentsList = departmentsList;
}
}
My Manager class (which the Action class calls to populate the list of Departments):
package com.test.controller;
import java.util.List;
import java.util.Iterator;
import org.hibernate.Criteria;
import org.hibernate.Hibernate;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import com.test.model.Departments;
import com.test.util.HibernateUtil;
public class DepartmentsManager {
public List<Departments> list() {
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
List<Departments> set = null;
try {
Query q = session.createQuery("FROM Departments");
/*Query q = session.createQuery("FROM Departments d JOIN FETCH d.employeeses e");*/
q.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
set = (List<Departments>) q.list();
} catch (HibernateException e) {
e.printStackTrace();
session.getTransaction().rollback();
}
session.getTransaction().commit();
return set;
}
}

Lazy collections work only within the scope of the transaction (where the owning entity was retrieved from a DB). In other words, you should not pass a Hibernate entity with non-loaded lazy sub-entities or collections outside the transaction scope.
You need either to build another entity or use lazy="false" if you want to pass an entity to JSP, or serialization code or anything else.

Two simple ways to manage lazy loading within view :
Using a Transaction view (consisting in wrapping view calls into JTA transaction (application-managed for instance)
Using an extented persistence context in your bean and flushing it explicitely when you've done with it, that means as soon as you were able to load your lazy objects.
For more information, check this post and the answer that belongs to it:
JPA lazy loading Collections in JSF view - better way than using Filters?

How to avoid endless loop in Hibernate when fetching bidirectional collections?

I am trying to populate some entity objects in a very simple Hibernate example. My database consists of two tables, "Departments" (Id, Name) and "Employees" (Id, DepartmentsId, FirstName, LastName). My SQL query is simply a left join of Employees to Departments.
I have set up the annotations as specified in the Hibernate documentation, but whenever I try to serialize the entities Hibernate goes into an endless loop and eventually throws a StackOverFlowError exception. Someone answering another question of mine was able to determine that the stack overflow is happening because the "Department" object contains a set of "Employee" objects, which each contain a "Department" object, which contains a set of Employee objects, etc. etc.
This type of bidirectional relationship is supposed to be legal as per the documentation linked above (the "mappedBy" parameter in Department is supposed to clue Hibernate in; I have also tried using the "joinColumn" annotation that is commented out in the code below), and other things I have read indicate the Hibernate is supposed to be smart enough not to go into an endless loop in this situation, but it is not working for my example. Everything works fine if I change the bidirectional relationship to a unidirectional relationship by removing the Department object from the Employee class, but obviously this causes the loss of a lot of functionality.
I have also tried foregoing the annotations for the older xml mapping files and setting the "inverse" parameter for the child table, but it still produces the same problem. How can I get this bidirectional relationship working the way it is supposed to work?
Department:
package com.test.model;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.JoinTable;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.JoinColumn;
import org.hibernate.Hibernate;
import org.hibernate.proxy.HibernateProxy;
#Entity
#Table(name="Departments"
,catalog="test"
)
public class Department implements java.io.Serializable {
private Integer id;
private String name;
public Set<Employee> employees = new HashSet<Employee>(0);
public Department() {
}
public Department(String name) {
this.name = name;
}
public Department(String name, Set employees) {
this.name = name;
this.employees = employees;
}
#Id #GeneratedValue(strategy=IDENTITY)
#Column(name="Id", unique=true, nullable=false)
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
#Column(name="Name", nullable=false)
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
#OneToMany(fetch=FetchType.LAZY, mappedBy="department")
/*#OneToMany
#JoinColumn(name="DepartmentsId")*/
public Set<Employee> getEmployees() {
return this.employees;
}
public void setEmployees(Set employees) {
this.employees = employees;
}
}
Employee:
package com.test.model;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.JoinTable;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
#Entity
#Table(name="Employees"
,catalog="test"
)
public class Employee implements java.io.Serializable {
private Integer id;
private Department department;
private String firstName;
private String lastName;
public Employee() {
}
public Employee(Department department, String firstName, String lastName) {
this.department = department;
this.firstName = firstName;
this.lastName = lastName;
}
#Id #GeneratedValue(strategy=IDENTITY)
#Column(name="Id", unique=true, nullable=false)
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
#ManyToOne
#JoinColumn(name="DepartmentsId", nullable=false, insertable=false, updatable=false)
public Department getDepartment() {
return this.department;
}
public void setDepartment(Department department) {
this.department = department;
}
#Column(name="FirstName", nullable=false)
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
#Column(name="LastName", nullable=false)
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
Department Manager (Contains the HQL query):
package com.test.controller;
import java.util.Collections;
import java.util.List;
import java.util.Iterator;
import org.hibernate.Criteria;
import org.hibernate.Hibernate;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import com.test.model.Department;
import com.test.util.HibernateUtil;
public class DepartmentManager extends HibernateUtil {
public List<Department> list() {
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
List<Department> set = null;
try {
Query q = session.createQuery("FROM Department d JOIN FETCH d.employees e");
q.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
set = (List<Department>) q.list();
} catch (HibernateException e) {
e.printStackTrace();
session.getTransaction().rollback();
}
session.getTransaction().commit();
return set;
}
}

In general, you should not serialize your entities. Circular dependencies and proxies make that hard. Instead, you should manually transfer the data you need to send to a DTO (a new data-only class), and serialize it instead. It won't have the lazy collections, proxies, and whatnot.

For complement the top response i did a generic convert who do the job for me, transfering the entity values to DTO object, you just have to make your dto fields with the same name from the mapped entity.
Here is the source code.
/**
* Atribui os valores de campos correspondentes de um objeto para um outro objeto de destino. Os
* campos do objeto de destino que ja estiverem preenchidos nao serao substituidos
*
* #param objetoOrigem
* #param objetoDestino
* #return
* #throws NegocioException
*/
public static <T1, T2> T2 convertEntity(T1 objetoOrigem, T2 objetoDestino) throws NegocioException {
if (objetoOrigem != null && objetoDestino != null) {
Class<? extends Object> classe = objetoOrigem.getClass();
Class<? extends Object> classeDestino = objetoDestino.getClass();
Field[] listaCampos = classe.getDeclaredFields();
for (int i = 0; i < listaCampos.length; i++) {
Field campo = listaCampos[i];
try {
Field campoDestino = classeDestino.getDeclaredField(campo.getName());
campo.setAccessible(true);
campoDestino.setAccessible(true);
atribuiValorAoDestino(objetoOrigem, objetoDestino, campo, campoDestino);
} catch (NoSuchFieldException e) {
LOGGER.log(Logger.Level.TRACE, (Object) e);
continue;
} catch (IllegalArgumentException | IllegalAccessException e) {
LOGGER.error(e.getMessage(), e);
throw new NegocioException(e.getMessage(), EnumTypeException.ERROR);
}
}
}
return objetoDestino;
}