Vardhan: Hibernate Interview Questions

1.What is ORM ?

ORM stands for object/relational mapping. ORM is the automated persistence of objects in a Java application to the tables in a relational database.

2.What does ORM consists of ?

An ORM solution consists of the followig four pieces:

API for performing basic CRUD operations
API to express queries refering to classes
Facilities to specify metadata
Optimization facilities : dirty checking,lazy associations fetching

3.What are the ORM levels ?

The ORM levels are:

Pure relational (stored procedure.)
Light objects mapping (JDBC)
Medium object mapping
Full object Mapping (composition,inheritance, polymorphism, persistence by reachability)

4.What is Hibernate?

Hibernate is a pure Java object-relational mapping (ORM) and persistence framework that allows you to map plain old Java objects to relational database tables using (XML) configuration files.Its purpose is to relieve the developer from a significant amount of relational data persistence-related programming tasks.

5.Why do you need ORM tools like hibernate?

The main advantage of ORM like hibernate is that it shields developers from messy SQL. Apart from this, ORM provides following benefits:

Improved productivity

High-level object-oriented API
Less Java code to write
No SQL to write

Improved performance

Sophisticated caching
Lazy loading
Eager loading

Improved maintainability

A lot less code to write

Improved portability

ORM framework generates database-specific SQL for you

6.What Does Hibernate Simplify?

Hibernate simplifies:

Saving and retrieving your domain objects
Making database column and table name changes
Centralizing pre save and post retrieve logic
Complex joins for retrieving related items
Schema creation from object model

7.What is the need for Hibernate xml mapping file?

Hibernate mapping file tells Hibernate which tables and columns to use to load and store objects. Typical mapping file look as follows:

8.What are the most common methods of Hibernate configuration?

The most common methods of Hibernate configuration are:

Programmatic configuration
XML configuration (hibernate.cfg.xml)

9.What are the important tags of hibernate.cfg.xml?

Following are the important tags of hibernate.cfg.xml:

10.What are the Core interfaces are of Hibernate framework?

The five core interfaces are used in just about every Hibernate application. Using these interfaces, you can store and retrieve persistent objects and control transactions.

Session interface
SessionFactory interface
Configuration interface
Transaction interface
Query and Criteria interfaces

11.What role does the Session interface play in Hibernate?

The Session interface is the primary interface used by Hibernate applications. It is a single-threaded, short-lived object representing a conversation between the application and the persistent store. It allows you to create query objects to retrieve persistent objects.

Session session = sessionFactory.openSession();

Session interface role:

Wraps a JDBC connection
Factory for Transaction
Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier

12.What role does the SessionFactory interface play in Hibernate?

The application obtains Session instances from a SessionFactory. There is typically a single SessionFactory for the whole applicationå¹¼reated during application initialization. The SessionFactory caches generate SQL statements and other mapping metadata that Hibernate uses at runtime. It also holds cached data that has been read in one unit of work and may be reused in a future unit of work

SessionFactory sessionFactory = configuration.buildSessionFactory();

13.What is the general flow of Hibernate communication with RDBMS?

The general flow of Hibernate communication with RDBMS is :

Load the Hibernate configuration file and create configuration object. It will automatically load all hbm mapping files
Create session factory from configuration object
Get one session from this session factory
Create HQL Query
Execute query to get list containing Java objects

14.What is Hibernate Query Language (HQL)?

Hibernate offers a query language that embodies a very powerful and flexible mechanism to query, store, update, and retrieve objects from a database. This language, the Hibernate query Language (HQL), is an object-oriented extension to SQL.

15.How do you map Java Objects with Database tables?

First we need to write Java domain objects (beans with setter and getter).
Write hbm.xml, where we map java class to table and database columns to Java class variables.

Example :

name="com.test.User" table="user">
   column="USER_NAME" length="255"
      name="userName" not-null="true" type="java.lang.String"/>
   column="USER_PASSWORD" length="255"
     name="userPassword" not-null="true" type="java.lang.String"/>

16.What’s the difference between load() and get()?

load() vs. get() :-

load()	get()
Only use the load() method if you are sure that the object exists.	If you are not sure that the object exists, then use one of the get()methods.
load() method will throw an exception if the unique id is not found in the database.	get() method will return null if the unique id is not found in the database.
load() just returns a proxy by default and database won’t be hit until the proxy is first invoked.	get() will hit the database immediately.

17.What is the difference between and merge and update ?

Use update() if you are sure that the session does not contain an already persistent instance with the same identifier, and merge() if you want to merge your modifications at any time without consideration of the state of the session.

18.How do you define sequence generated primary key in hibernate?

Using tag.
Example:-

column="USER_ID" name="id" type="java.lang.Long">
class="sequence">
name="table">SEQUENCE_NAME

19.Define cascade and inverse option in one-many mapping?

cascade - enable operations to cascade to child entities.
cascade="all|none|save-update|delete|all-delete-orphan"

inverse - mark this collection as the "inverse" end of a bidirectional association.
inverse="true|false"
Essentially "inverse" indicates which end of a relationship should be ignored, so when persisting a parent who has a collection of children, should you ask the parent for its list of children, or ask the children who the parents are?

20.What do you mean by Named – SQL query?

Named SQL queries are defined in the mapping xml document and called wherever required.
Example:

name = "empdetails">
   alias="emp" class="com.test.Employee"/>
    SELECT emp.EMP_ID AS {emp.empid},
                 emp.EMP_ADDRESS AS {emp.address},
                 emp.EMP_NAME AS {emp.name}
      FROM Employee EMP WHERE emp.NAME LIKE :name

Invoke Named Query :

List people = session.getNamedQuery("empdetails")
                                    .setString("TomBrady", name)
                                    .setMaxResults(50)
                                    .list();

21.How do you invoke Stored Procedures?

name="selectAllEmployees_SP" callable="true">
alias="emp" class="employee">

name="empid" column="EMP_ID"/>

name="name" column="EMP_NAME"/>

name="address" column="EMP_ADDRESS"/>
{ ? = call selectAllEmployees() }

22.Explain Criteria API

Criteria is a simplified API for retrieving entities by composing Criterion objects. This is a very convenient approach for functionality like "search" screens where there is a variable number of conditions to be placed upon the result set.
Example :

List employees = session.createCriteria(Employee.class)
                                      .add(Restrictions.like("name", "a%") )
                                        .add(Restrictions.like("address", "Boston"))
                                              .addOrder(Order.asc("name") )
                                              .list();

23.Define HibernateTemplate?

org.springframework.orm.hibernate.HibernateTemplate is a helper class which provides different methods for querying/retrieving data from the database. It also converts checked HibernateExceptions into unchecked DataAccessExceptions.

24.What are the benefits does HibernateTemplate provide?

The benefits of HibernateTemplate are :

· HibernateTemplate, a Spring Template class simplifies interactions with Hibernate Session.

Common functions are simplified to single method calls.
Sessions are automatically closed.
Exceptions are automatically caught and converted to runtime exceptions.

25.How do you switch between relational databases without code changes?

Using Hibernate SQL Dialects , we can switch databases. Hibernate will generate appropriate hql queries based on the dialect defined.

26.If you want to see the Hibernate generated SQL statements on console, what should we do?

In Hibernate configuration file set as follows:
name="show_sql">true

27.What are derived properties?

The properties that are not mapped to a column, but calculated at runtime by evaluation of an expression are called derived properties. The expression can be defined using the formula attribute of the element.

28.What is component mapping in Hibernate?

A component is an object saved as a value, not as a reference
A component can be saved directly without needing to declare interfaces or identifier properties
Required to define an empty constructor
Shared references not supported

Example:

29.What is the difference between sorted and ordered collection in hibernate?

sorted collection vs. order collection :-

sorted collection	order collection
A sorted collection is sorting a collection by utilizing the sorting features provided by the Java collections framework. The sorting occurs in the memory of JVM which running Hibernate, after the data being read from database using java comparator.	Order collection is sorting a collection by specifying the order-by clause for sorting this collection when retrieval.
If your collection is not large, it will be more efficient way to sort it.	If your collection is very large, it will be more efficient way to sort it .

31.What is the advantage of Hibernate over jdbc?

Hibernate Vs. JDBC :-

JDBC	Hibernate
With JDBC, developer has to write code to map an object model's data representation to a relational data model and its corresponding database schema.	Hibernate is flexible and powerful ORM solution to map Java classes to database tables. Hibernate itself takes care of this mapping using XML files so developer does not need to write code for this.
With JDBC, the automatic mapping of Java objects with database tables and vice versa conversion is to be taken care of by the developer manually with lines of code.	Hibernate provides transparent persistence and developer does not need to write code explicitly to map database tables tuples to application objects during interaction with RDBMS.
JDBC supports only native Structured Query Language (SQL). Developer has to find out the efficient way to access database, i.e. to select effective query from a number of queries to perform same task.	Hibernate provides a powerful query language Hibernate Query Language (independent from type of database) that is expressed in a familiar SQL like syntax and includes full support for polymorphic queries. Hibernate also supports native SQL statements. It also selects an effective way to perform a database manipulation task for an application.
Application using JDBC to handle persistent data (database tables) having database specific code in large amount. The code written to map table data to application objects and vice versa is actually to map table fields to object properties. As table changed or database changed then it’s essential to change object structure as well as to change code written to map table-to-object/object-to-table.	Hibernate provides this mapping itself. The actual mapping between tables and application objects is done in XML files. If there is change in Database or in any table then the only need to change XML file properties.
With JDBC, it is developer’s responsibility to handle JDBC result set and convert it to Java objects through code to use this persistent data in application. So with JDBC, mapping between Java objects and database tables is done manually.	Hibernate reduces lines of code by maintaining object-table mapping itself and returns result to application in form of Java objects. It relieves programmer from manual handling of persistent data, hence reducing the development time and maintenance cost.
With JDBC, caching is maintained by hand-coding.	Hibernate, with Transparent Persistence, cache is set to application work space. Relational tuples are moved to this cache as a result of query. It improves performance if client application reads same data many times for same write. Automatic Transparent Persistence allows the developer to concentrate more on business logic rather than this application code.
In JDBC there is no check that always every user has updated data. This check has to be added by the developer.	Hibernate enables developer to define version type field to application, due to this defined field Hibernate updates version field of database table every time relational tuple is updated in form of Java class object to that table. So if two users retrieve same tuple and then modify it and one user save this modified tuple to database, version is automatically updated for this tuple by Hibernate. When other user tries to save updated tuple to database then it does not allow saving it because this user does not have updated data.

32.What are the Collection types in Hibernate ?

Bag
Set
List
Array
Map

33.What are the ways to express joins in HQL?

HQL provides four ways of expressing (inner and outer) joins:-

An implicit association join
An ordinary join in the FROM clause
A fetch join in the FROM clause.
A theta-style join in the WHERE clause.

34.Define cascade and inverse option in one-many mapping?

cascade - enable operations to cascade to child entities.
cascade="all|none|save-update|delete|all-delete-orphan"

inverse - mark this collection as the "inverse" end of a bidirectional association.
inverse="true|false"
Essentially "inverse" indicates which end of a relationship should be ignored, so when persisting a parent who has a collection of children, should you ask the parent for its list of children, or ask the children who the parents are?

35.What is Hibernate proxy?

The proxy attribute enables lazy initialization of persistent instances of the class. Hibernate will initially return CGLIB proxies which implement the named interface. The actual persistent object will be loaded when a method of the proxy is invoked.

36.How can Hibernate be configured to access an instance variable directly and not through a setter method ?

By mapping the property with access="field" in Hibernate metadata. This forces hibernate to bypass the setter method and access the instance variable directly while initializing a newly loaded object.

37.How can a whole class be mapped as immutable?

Mark the class as mutable="false" (Default is true),. This specifies that instances of the class are (not) mutable. Immutable classes, may not be updated or deleted by the application.

38.What is the use of dynamic-insert and dynamic-update attributes in a class mapping?

dynamic-update (defaults to false): Specifies that UPDATE SQL should be generated at runtime and contain only those columns whose values have changed
dynamic-insert (defaults to false): Specifies that INSERT SQL should be generated at runtime and contain only the columns whose values are not null.

39.What do you mean by fetching strategy ?

A fetching strategy is the strategy Hibernate will use for retrieving associated objects if the application needs to navigate the association. Fetch strategies may be declared in the O/R mapping metadata, or over-ridden by a particular HQL or Criteria query.

40.What is automatic dirty checking?

Automatic dirty checking is a feature that saves us the effort of explicitly asking Hibernate to update the database when we modify the state of an object inside a transaction.

41.What is transactional write-behind?

Hibernate uses a sophisticated algorithm to determine an efficient ordering that avoids database foreign key constraint violations but is still sufficiently predictable to the user. This feature is called transactional write-behind.

42.What are Callback interfaces?

Callback interfaces allow the application to receive a notification when something interesting happens to an object—for example, when an object is loaded, saved, or deleted. Hibernate applications don't need to implement these callbacks, but they're useful for implementing certain kinds of generic functionality.

43.What are the types of Hibernate instance states ?

Three types of instance states:

Transient -The instance is not associated with any persistence context
Persistent -The instance is associated with a persistence context
Detached -The instance was associated with a persistence context which has been closed – currently not associated

45.What are the types of inheritance models in Hibernate?

There are three types of inheritance models in Hibernate:

Table per class hierarchy
Table per subclass
Table per concrete class

46. Difference between session.save() , session.saveOrUpdate() and session.persist()?

session.save() : Save does an insert and will fail if the primary key is already persistent.

session.saveOrUpdate() : saveOrUpdate does a select first to determine if it needs to do an insert or an update. Insert data if primary key not exist otherwise update data.

session.persist() : Does the same like session.save(). But session.save() return Serializable object but session.persist() return void. session.save() returns the generated identifier (Serializable object) and session.persist() doesn't.

For Example :

if you do :-

System.out.println(session.save(question));

This will print the generated primary key.

if you do :-

System.out.println(session.persist(question));

Compile time error because session.persist() return void.

47. What is lazy fetching in Hibernate? With Example .

Lazy fetching decides whether to load child objects while loading the Parent Object.

You need to do this setting respective hibernate mapping file of the parent class.

Lazy = true (means not to load child)

By default the lazy loading of the child objects is true.

This make sure that the child objects are not loaded unless they are explicitly invoked in the application by calling getChild() method on parent.In this case hibernate issues a fresh database call to load the child when getChild() is actully called on the Parent object.But in some cases you do need to load the child objects when parent is loaded.

Just make the Lazy=false and hibernate will load the child when parent is loaded from the database.

Example :

If you have a TABLE EMPLOYEE mapped to Employee object and contains set of Address objects.

Parent Class : Employee class

Child class : Address Class

public class Employee {

private Set address = new HashSet(); // contains set of child Address objects

public Set getAddress () {

return address;

}

public void setAddresss(Set address) {

this. address = address;

}

In the Employee.hbm.xml file

<one-to-many class="beans Address"/>

</set>

In the above configuration.

If lazy="false" : - when you load the Employee object that time child object Adress is also loaded and set to setAddresss() method.

If you call employee.getAdress() then loaded data returns. No fresh database call.

If lazy="true" :- This the default configuration. If you dont mention then hibernate consider lazy=true.

when you load the Employee object that time child object Adress is not loaded. You need extra call to data base to get address objects.

If you call employee.getAdress() then that time database query fires and return results. Fresh database call.

48. Difference between session.saveOrUpdate() and session.merge();

saveOrUpdate() does the following:

Ø if the object is already persistent in this session, do nothing

Ø if another object associated with the session has the same identifier, throw an exception

Ø if the object has no identifier property, save() it

Ø if the object's identifier has the value assigned to a newly instantiated object, save() it

Ø if the object is versioned (by a <version> or <timestamp>), and the version property value is the same value assigned to a newly instantiated object, save() it

Ø otherwise update() the object

merge() is very different:

Ø if there is a persistent instance with the same identifier currently associated with the session, copy the state of the given object onto the persistent instance

Ø if there is no persistent instance currently associated with the session, try to load it from the database, or create a new persistent instance

Ø the persistent instance is returned

Ø the given instance does not become associated with the session, it remains detached

49.How to prevent concurrent update in Hibernate?

Version checking used in hibernate when more than one thread trying to access same data.

For example :

User A edit the row of the TABLE for update (In the User Interface changing data - This is user thinking time) and in the same time User B edit the same record for update and click the update.

Then User A click the Update and update done. Change made by user B is gone.

In hibernate you can prevent slate object updation using version checking.

Check the version of the row when you are updating the row.

Get the version of the row when you are fetching the row of the TABLE for update.

On the time of updation just fetch the version number and match with your version number (on the time of fetching).

This way you can prevent slate object updation.

Steps 1:

Declare a variable "versionId" in your Class with setter and getter.

public class Campign {

private Long versionId;

private Long campignId;

private String name;

public Long getVersionId() {

return versionId;

}

public void setVersionId(Long versionId) {

this.versionId = versionId;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public Long getCampignId() {

return campignId;

}

private void setCampignId(Long campignId) {

this.campignId = campignId;

}

Step 2:-

In the .hbm.xml file

<param name="sequence">CAMPIGN_ID_SEQ</param>

</generator>

</id>

</class>

Step 3:-

Create a coulmn name "version" in the CAMPIGN table.

Step 4:-

In the code

// foo is an instance loaded by a previous Session

session = sf.openSession();

int oldVersion = foo.getVersion();

session.load( foo, foo.getKey() );

if ( oldVersion!=foo.getVersion ) throw new StaleObjectStateException();

foo.setProperty("bar");

session.flush();

session.connection().commit();

session.close();

You can handle StaleObjectStateException() and do what ever you want.

You can display error message. Hibernate autumatically create/update the version number when you update/insert any row in the table.

50. How to set 2nd level cache in hibernate with EHCache?

When you are creating SessionFactory just add the below steps

String ecache = appHome+File.separatorChar+"ehcache.xml";

try {

CacheManager.create(ecache);

} catch (CacheException e) {

// logger.logError(e);

}*/

Then

sessionFactory = configuration.buildSessionFactory();

ECache.xml is like

<ehcache>

<defaultCache maxElementsInMemory="10000" eternal="false"

timeToIdleSeconds="120" timeToLiveSeconds="120" overflowToDisk="true"

diskPersistent="false" diskExpiryThreadIntervalSeconds="120" />

<cache name="bean.ApplicationBean" maxElementsInMemory="300"

eternal="false" overflowToDisk="false" />

</ehcache>

ApplicationBean will be avilable in 2nd level cache

51. Difference between list() and iterate() i9n Hibernate?

If instances are already be in the session or second-level cache iterate() will give better performance.

If they are not already cached, iterate() will be slower than list() and might require many database hits for a simple query.

52. Difference between getCurrentSession() and openSession() in Hibernate ?

getCurrentSession() :

The "current session" refers to a Hibernate Session bound by Hibernate behind the scenes, to the transaction scope.

A Session is opened when getCurrentSession() is called for the first time and closed when the transaction ends.

It is also flushed automatically before the transaction commits. You can call getCurrentSession() as often and anywhere you want as long as the transaction runs.

To enable this strategy in your Hibernate configuration:

set hibernate.transaction.manager_lookup_class to a lookup strategy for your JEE container

set hibernate.transaction.factory_class to org.hibernate.transaction.JTATransactionFactory

Only the Session that you obtained with sf.getCurrentSession() is flushed and closed automatically.

Example :

try {

UserTransaction tx = (UserTransaction)new InitialContext() .lookup("java:comp/UserTransaction");

tx.begin();

// Do some work

sf.getCurrentSession().createQuery(...);

sf.getCurrentSession().persist(...);

tx.commit();

}

catch (RuntimeException e) {

tx.rollback();

throw e; // or display error message

}

openSession() :

If you decide to use manage the Session yourself the go for sf.openSession() , you have to flush() and close() it.

It does not flush and close() automatically.

Example :

UserTransaction tx = (UserTransaction)new InitialContext() .lookup("java:comp/UserTransaction");

Session session = factory.openSession();

try {

tx.begin();

// Do some work

session.createQuery(...);

session.persist(...);

session.flush(); // Extra work you need to do

tx.commit();

}

catch (RuntimeException e) {

tx.rollback();

throw e; // or display error message

}

finally {

session.close(); // Extra work you need to do

}

53. One To Many Bi-directional Relation in Hibernate?

Bi-DireCtional One to Many Relation- EXAMPLE

PROCESS_TYPE_LOV (PROCESS_TYPE_ID number, PROCESS_TYPE_NAME varchar) - TABLE

PROCESS (PROCESS_ID number,PROCESS_NAME varchar,PROCESS_TYPE_ID number)- TABLE

public class ProcessTypeBean {

private Long processTypeId;

private String processTypeName;

private List processes = null;

/**

* @return Returns the processes.

public List getProcesses() {

return processes;

}

/**

* @param processes The processes to set.

public void setProcesses(List processes) {

this.processes = processes;

}

/**

* @return Returns the processTypeId.

public Long getProcessTypeId() {

return processTypeId;

}

/**

* @param processTypeId The processTypeId to set.

public void setProcessTypeId(Long processTypeId) {

this.processTypeId = processTypeId;

}

/**

* @return Returns the processTypeName.

public String getProcessTypeName() {

return processTypeName;

}

/**

* @param processTypeName The processTypeName to set.

public void setProcessTypeName(String processTypeName) {

this.processTypeName = processTypeName;

}

public class ProcessBean {

private Long processId;

private String processName = "";

private ProcessTypeBean processType;

public Long getProcessId() {

return processId;

}

/**

* @param processId The processId to set.

public void setProcessId(Long processId) {

this.processId = processId;

}

/**

* @return Returns the processName.

public String getProcessName() {

return processName;

}

/**

* @param processName The processName to set.

public void setProcessName(String processName) {

this.processName = processName;

}

/**

* @return Returns the processType.

public ProcessTypeBean getProcessType() {

return processType;

}

/**

* @param processType The processType to set.

public void setProcessType(ProcessTypeBean processType) {

this.processType = processType;

}

<many-to-one name="processType" column="PROCESS_TYPE_ID" lazy="false" />

</class>

<one-to-many

class="com.bean.ProcessBean" />

</bag>

</class>

54. One To Many Mapping Using List ?

WRITER (ID INT,NAME VARCHAR) - TABLE

STORY (ID INT,INFO VARCHAR,PARENT_ID INT) - TABLE

One writer can have multiple stories..

-------------------------------------------------------------

Mapping File...

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping

PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

</id>

<one-to-many class="Story"/>

</list>

</class>

</id>

</class>

</hibernate-mapping>

-------------------------------------------------------

public class Writer {

private int id;

private String name;

private List stories;

public void setId(int i) {

id = i;

}

public int getId() {

return id;

}

public void setName(String n) {

name = n;

}

public String getName() {

return name;

}

public void setStories(List l) {

stories = l;

}

public List getStories() {

return stories;

}

---------------------------------------------------

public class Story {

private int id;

private String info;

public Story(){

}

public Story(String info) {

this.info = info;

}

public void setId(int i) {

id = i;

}

public int getId() {

return id;

}

public void setInfo(String n) {

info = n;

}

public String getInfo() {

return info;

}

----------------------------------------------------

Save Example ..

Writer wr = new Writer();

wr.setName("Das");

ArrayList list = new ArrayList();

list.add(new Story("Story Name 1"));

list.add(new Story("Story Name 2"));

wr.setStories(list);

Transaction transaction = null;

try {

transaction = session.beginTransaction();

session.save(sp);

transaction.commit();

} catch (Exception e) {

if (transaction != null) {

transaction.rollback();

throw e;

}

} finally {

session.close();

}

55.Many To Many Relation In Hibernate ?

Best Example. For Many to Many in Hibernate ..

EVENTS ( uid int, name VARCHAR) Table

SPEAKERS ( uid int, firstName VARCHAR) Table

EVENT_SPEAKERS (elt int, event_id int, speaker_id int) Table

-----------------------------------------------------------

import java.util.Set;

import java.util.HashSet;

public class Speaker{

private Long id;

private String firstName;

private Set events;

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 Set getEvents() {

return this.events;

}

public void setEvents(Set events) {

this.events = events;

}

private void addEvent(Event event) {

if (events == null) {

events = new HashSet();

}

events.add(event);

}

--------------------------------------------------------

import java.util.Date;

import java.util.Set;

public class Event{

private Long id;

private String name;

private Set speakers;

public void setId(Long id) {

this.id = id;

}

public Long getId() {

return id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public void setSpeakers(Set speakers) {

this.speakers = speakers;

}

public Set getSpeakers() {

return speakers;

}

--------------------------------------------------------------

Event.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 2.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

</id>

<many-to-many class="Speaker"/>

</set>

</class>

</hibernate-mapping>

------------------------------------------------------------------

Speaker.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 2.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

</id>

<many-to-many class="Event"/>

</set>

</class>

</hibernate-mapping>

----------------------------------------------------------------------

Save and Fetch Example

Event event = new Event();

event.setName("Inverse test");

event.setSpeakers(new HashSet());

event.getSpeakers().add(new Speaker("Ram", event));

event.getSpeakers().add(new SpeakerManyToMany("Syam", event));

event.getSpeakers().add(new SpeakerManyToMany("Jadu", event));

session.save(event); /// Save All the Data

event = (Event) session.load(Event.class, event.getId());

Set speakers = event.getSpeakers();

for (Iterator i = speakers.iterator(); i.hasNext();) {

Speaker speaker = (Speaker) i.next();

System.out.println(speaker.getFirstName());

System.out.println(speaker.getId());

}

Vardhan

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Sunday, May 20, 2012

Hibernate Interview Questions

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