Hibernate Training Day 1

8/2/2019 Hibernate Training Day 1

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CONFIDENTIAL

Hibernate Object Relation MapperNovember 24, 2008


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Purpose

To learn about hibernate persistence framework and its architecture

To learn how hibernate is configured and what are the componentsrequired in an application using hibernate

To learn what are the types of objects and how to work with them

To understand various associations & how to map them.

To master HQL and other fetching strategies

To learn inheritance and component mapping

To understand how to modify data

An overview of cache management, transaction management andother advanced features


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Introduction to different ways of persisting data

Without Databases

Object Serialization

Uses the file system for storing the serialized object forms. Not a object relation mapping technique. Only accessible through java language. Bad choice for storing enterprise data.

With Databases (RDBMS )

JDBC

Simply provide API accessing database, No object relation mapping technique

Database dependent code Entity Beans (BMP and CMP)

EJB require a one-to-one mapping to database tables Requires application server supporting EJB Container

JDO

Commercial from individual vendors. Mappings not standard

O/R Mapping tool like Hibernate

Rich features with total abstraction to databases. Provides resolutions to majority concerns on OR mapping.


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Object Serialization Example

Creating a simple Hashtable and serialize it to a file calledHTExample.ser.

FileOutputStream fileOut = new FileOutputStream("HTExample.ser");

ObjectOutputStream out = new ObjectOutputStream(fileOut);out.writeObject(h); //h is an hashMap object with values.

Reading the Serialized object data stored in the file to theactual object:

FileInputStream fileIn = new FileInputStream("HTExample.ser");ObjectInputStream in = new ObjectInputStream(fileIn);

h = (Hashtable)in.readObject();


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JDBC Example

JDBC API used for writing database applications in Javaby making database connections.

Loading a database driver :

Class.forName(com.mysql.jdbc.Driver);

Creating a mysql jdbc ConnectionConnection conn = DriverManager.getConnection(

jdbc:mysql://localhost:3306/hibernate, root, root);

Creating a jdbc Statement object

* Statement * Prepared Statement * Callable Statement

Executing a SQL statement with the Statement object, andreturning a jdbc resultSet.


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ORM


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Object relation mapping fundamentals

Objects to integrate into Relational model

Object modeling describes system through objects, Association, behavior, state, inheritance

Relational modeling describes system through information. Relation, Attribute, Domain

Object-relational mapping is the process of transforming between object and relational modelingapproaches


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Object relation mapping - Advantages

Natural programming model

Reduced Line Of Code Code can be run / Tested out side the container

Classes may be reused in non persistence context

Minimum database access with smart fetching strategies

Opportunities for aggressive caching

Structural mapping more robust when Object/Relational data model changes.


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Introduction to Hibernate


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Why Hibernate ?

Open sourcePersistence for java beans or POJO

Relieves from manual ResultSet Handling

Easy Switching to other SQL database

Powerful queries

Extensive RDBMS support

Tools support

Integrates elegently


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RDBMS Support

Hibernate is tested with wide range of databases.

DB2 7.1, 7.2; MySQL 3.23;

PostgreSQL 7.1.2, 7.2, 7.3;

Oracle 8i, 9i;

Sybase 12.5 (JConnect 5.5);

Interbase 6.0.1 (Open Source)

With Firebird InterClient 2.01;

HypersonicSQL 1.61, 1.7.0;

Microsoft SQL Server 2000;

Mckoi SQL 0.93

Progress 9

Pointbase Embedded 4.3

SAP DB 7.3


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Tools Support

Modeling tools / Code generator

Middlegen

AndroMDA

XDoclet

IDE Plug-in support:

RSA, JBOSS, Eclipse WTP


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Hibernate application components

Hibernate Libraries

Hibernate configuration file

Hibernate mapping files (HBM files)

POJO classes

Main class


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Hibernate Environment

antlr.jar

cglib.jarasm.jarasm-attrs.jarscommons-collections.jar

commons-logging.jarhibernate3.jarjta.jardom4j.jar

log4j.jar


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Hibernate configuration property file

Used for configuring hibernate Contains

- Database Configuration- Datasource Configuration- Transaction Configuration- Caching Configuration

- ConnectionPool Configuration- Other Settings.


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Hibernate Configuration

com.mysql.jdbc.Driverjdbc:mysql://localhost:3306/hibernaterootrootorg.hibernate.dialect.MySQLDialecttrueupdate


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The hibernate-mapping configuration file

Object to relation mappings are often defined in a xml file Mapping file can be hand written or edited. Java Centric persistence classes. No. of tools available to generate the configuration.

-AndroMDA-XDoclets

-Middlegen Standard DTD for correct implementation


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Hibernate XML Configuration - Employee.hbm.xml


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Persisting the Employee

SessionFactory sf = Configuration.configure().buildSessionFactory();Session session = sf.OpenSession();Transaction tx = session.beginTransaction();

Employee emp = new Employee()emp.setEmail(sadinenijayadev @yahoo.co.in);

emp.setName(Jayadev S);emp.setSalary(13331);session.save(emp);

Tx.commit();session.close();


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Loading the Employee

Try{SessionFactory sf = Configuration.configure().buildSessionFactory();Session session = sf.OpenSession();Transaction tx = session.beginTransaction();

Employee emp = session.get(Employee.Class, new Long(1));

System.out.println(Employee salary : + emp.getSalary());

Tx.commit();

}Catch(HibernateException e){e.printStackTrace();

}


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Hibernate Architecture


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Hibernate Architecture

Responsibilities of architecture

-Manage connection with the database

-Converts HQL (Hibernate Query Language)statements to database specific statement.

-Manage result set on its own.

-Performs mapping of these database specific

data to Java objects which are directly used byJava application.


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Hibernate Architecture Core Interfaces

Hibernate Core interfaces

SessionFactory Interface

Hibernate Session provider

Single instance per application/data source.

Caches generated SQL statements and other mapping metadata.

Session interface

Hibernate session can be termed as a collection of loaded objects relating toa single unit of work.

This Is the primary interface used by the Hibernate application.

Hibernate Session are not thread safe hence by design be used one sessionper thread.

Configuration Interface

The Configuration object is used to configure and bootstrap Hibernate.

Application uses Configuration instance to specify the location of mappingfiles.


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Hibernate Architecture - Core Interfaces

Transaction Interface

The Transaction interface is an optional API. User might choose to use JDBC Tx, JTA

Abstracts the application code by the underlying transaction implementations. Helps to keep hibernate application portable between different kind of execution environments.

Query and Criteria Interfaces.

Manages and controls query execution

Queries can be written in HQL or in native SQL.

Criteria interfaces allows you to create execute object oriented criteria queries.

Callbackinterfaces

Allow the application to receive notification when a transaction happens to an object. Eg. when the object is loaded,deleted, saved.

Hibernate interfaces are not needed to be implemented but are useful sometimes.

Types

Extension Interfaces

Interfaces that allow extension of Hibernates powerful mapping functionality, such as UserType,CompositeUserType, and IdentifierGenerator.


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Hibernate Architecture - Elements

General steps:

/* Load the Hibernate configuration file and create configuration object. It willautomatically load all hbm mapping files. */

Configuration cfg = new Configuration();

cfg.configure(CONFIG_FILE_LOCATION);

/* Create session factory from configuration object */

SessionFactory sessionFactory = cfg.buildSessionFactory();

/* Get one session from this session factory. */

Session session = sessionFactory.openSession();

/* Create HQL query. */Query query = session.createQuery("from EmployeeBean);

/* Execute query to get list containing Java objects. */

List finalList = query.list();


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Hibernate Persistent ClassesNovember 24, 2008


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Persistent classes

Persistent classes are classes in an application that

implement the entities of the business problemExamples:

Employee

Customer Order

Item

Hibernate persistent classes implement POJOfundamentals

POJO Rules


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POJO Rules

Implement a no-argument constructor

Required for runtime proxy generation using

Constructor.newInstance()

Constructor must have atleast package visibility

Provide an identifier property (optional)

Some functionalities (transitive persistence) require identifier

Consistently-named

Nullable (Non-primitive) type

Prefer non-final classes (optional)

Mandatory for proxying

Performance tuning

Declare accessors and mutators for persistent fields (optional)

Can persist a property with default, protected or private get/set pair

POJO l


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POJO example

public class Parent implements Serializable { //Implements serializable

private long id; //Identifier property

private Set child;

public Parent() {} //No arg constructor

public String getId() { //Accessor methods

return id;

}

public void setId(long id) {

this.id = id;}

public Set getChild() {

return child;

}

public void setChild(Set child) {

this.child =child;

. //Some Logic}

public MonetaryDetails calcInvestment (Child child) {

... //Business method

}

}

POJO R l


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POJO Rules

Implement equals & hashCode() methods

Hibernate guarantees equivalence of objects only insession scope

Necessary for scenarios where instances are stored in a

Set or are reattached to the session Necessary for the problem with differences between

object identity in the virtual machine (VM) and objectidentity in the database.

POJO Rules Example


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POJO Rules Example

public class User {

...

public boolean equals(Object obj) {

if (obj == null) return false;

if (obj == this) return true;

if (obj.getClass() != getClass()) return false;

Child child = (Child) obj;

if (this.getFirstName().equals(child.getFirstName())

&& this.getLastName().equals(child.getLastName())) {

return true;

}

return false;

}

public int hashCode() {int tmp = 0;

tmp = (firstName +lastName).hashCode();

return tmp;

}

}

i t th d


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persistence methods

The following are the methods used to write the object tothe database:

save()

persist()

update()

saveOrUpdate()

merge()

Example


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Example

Example using Persistence methods.

PersistenceManage manage= new PersistenceManage();

Session session = HibernateUtil.currentSession();Transaction t = session.beginTransaction();

Singer singer = new Singer ();

manage.saveSinger(singer, session);

manage.persistSinger(singer, session);

manage.saveUpdateSinger(singer, session);manage.mergeSinger(singer, session);

if (session != null && session.isOpen()) {

if(t.isActive()) {

t.commit();

HibernateUtil.closeSession();

}

}


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Working with objects

Wh t i T i t Obj t?


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What is a Transient Object?

I want to insert a new User into the database!!!

Create a new User object

Employee newEmp = new Employee();

newEmp.setUserName(JOHN);

newEmp.setEmailId([email protected]);

All work described was performed by Capgemini or a Capgemini affiliate

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Wh t i i t t Obj t?


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What is persistent Object?

Obtain session object and save newEmp

SessionFactory sf = Configuration.configure().buildSessionFactory();

Session session = sf.OpenSession();

Transaction tx = session.beginTransaction();

session.save(newEmp);

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

tx.commit();

session.close();


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What is a detached object?


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What is a detached object?

After the session is closed, I want the id.

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


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Persistence Lifecycle


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Persistence Lifecycle


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Transient objects


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Transient objects

Not associated with database, table or row

If not referenced, they are inaccessible and valid forgarbage collection

They are non-transactional

To convert transient object to persistent object

Call to save() or saveOrUpdate()

creation of a reference from an already persistent

instance.


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Persistent Objects


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Persistent Objects

Any instance with a database identity

Associated with a Session and are transactional

State is synchronized with the database at variousinstances and changes are propagated

Automatic Dirty Checking

Call to delete() makes a persistent object transient.


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Detached Objects


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Detached Objects

Instances lose their association with persistence managerwhen session is closed

They contain persistent data (which might be stale later)

State is no longer guaranteed to be synchronized with db

state Can be re-associated with a session again using

session.lock()

Explicit detachment operation is also provided by

hibernate, Session.evict()


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Update persistent state of detached object


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Update persistent state of detached object

Employee emp1 = new Employee();

Transaction tx1 = sess.beginTransaction();

emp1.setName(name);emp1.setSalary(sal);

emp1.setEmail(email);

sess.save(emp1);

tx1.commit();

sess.close();

//Without forcing an update

Session sessionTwo = HibernateUtil.currentSession();

Transaction tx2 = sessionTwo.beginTransaction();

sessionTwo.lock(emp1, LockMode.NONE);

emp1.setName(Good Man");

emp1.setEmail ([email protected]");

tx2.commit();

sessionTwo.close();


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Retrieving a persistent object


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Session.load()

//Get the object with a given identifier

long id = 1

Employee emp = (Employee) session.load(Employee.class, new Long(id));

//Load state of employee in a new object of your own

Employee newEmp = new Employee ();

Session.load(newEmp, new Long(id));

Used when a row with given identifier definitely exist in database


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Session.get()

//Get the object with a given identifier

long id = 1

Employee user = (Employee) session.get(Employee.class, new Long(id));

Used when we are not sure that a row with given identifier exist in the database

Returns null if row doesnt exist


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Re loading persistent object


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Re-loading persistent object

session.refresh();

sess.save(emp);

sess.flush(); //force the SQL INSERT

sess.refresh(emp);

Generally used when database triggers are used to initialize some of the properties ofan object

Loads the object, synchronizes with the DB.


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Making objects Transient


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//Making Persistent Object Transient

Session session = sessions.openSession();

Transaction tx = session.beginTransaction();int userID = 1234;

Employee emp = (Employee) session.get(Employee.class, new Long(userID)); // emp is

//in persistent state

session.delete(emp); //emp moved to transient state

tx.commit();

session.close();

//Making Detached Object Transients

session.save(emp);

session.close();

Emp = new Employee(); //or we need to make the detached to the Persistent then delete

Session session2 = sessions.openSession();

session2.delete(emp);


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Flushing Session


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Flushing Session

session.flush()

Session will execute the SQL statements needed to synchronize the JDBC

connections state with the state of objects held in memory.

Executed at following points:

before some query executions

from org.hibernate.Transaction getting committed.

from Session.flush() calling explicitly

SQL fired in following order

all entity insertions, in the same order the corresponding objects were saved using Session.save()

all entity updates

all collection element deletions, updates and insertions

all entity deletions, in the same order the corresponding objects were deleted using Session.delete()


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Hibernate Training Day 1

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