Hibernet Object Relation

Hibernate – Object Relation Mapper -Gopal Patel

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Agenda           

Introduction to different ways of persisting data Object relation mapping fundamentals Hibernate Architecture Hibernate Environment Hibernate Round Trip development Features of hibernate RDBMS Support Tools support References to get started Project Architecture & Hibernate layer in Application Examples in depth CONFIDENTIAL

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Introduction to different ways of persisting data Without Databases

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Object Serialization   

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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  

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Entity Beans (BMP and CMP)  

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

JDO  

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Simply provide API accessing database, No object relation mapping technique Database dependent code

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 relation mapping fundamentals  

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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 modeling approaches

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Object Relation Mapping Advantages        

No more SQL/JDBC CRUD hand coded operations. Natural programming model (OODBMS) Reduced Line Of Code Code can be run / Tested out side the container (Will see) 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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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 by Java application.

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Hibernate Architecture Elements

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Hibernate Architecture – Core Interfaces 

Hibernate Core interfaces 

Session interface   

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SessionFactory Interface   

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Hibernate session can be termed as a collection of loaded objects relating to a 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 session per thread.

Hibernate Session provider Single instance per application/data source. Caches generated SQL statements and other mapping metadata.

Configuration Interface  

The Configuration object is used to configure and bootstrap Hibernate. Application uses Configuration instance to specify the location of mapping files.

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Hibernate Architecture - Core Interfaces 

Transaction Interface   

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Query and Criteria Interfaces.   

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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.

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.

Callback interfaces  

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.

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Types

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Extension Interfaces 

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

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Hibernate Architecture Elements  

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General steps: /* Load the Hibernate configuration file and create configuration object. It will automatically load all hbm mapping files. */ Configuration cfg = new Configuration(); cfg.configure(CONFIG_FILE_LOCATION);

/* Create session factory from configuration object */ SessionFactory sessionFactory = cfg.buildSessionFactory();

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

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Session session = sessionFactory.openSession();

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

/* Execute query to get list containing Java objects. */ List<EmployeeBean> finalList = query.list(); CONFIDENTIAL

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Hibernate Environment Lib - antlr.jar - cglib-full.jar - asm.jar - asm-attrs.jar - commons-collection.jar - commons-logging.jar - ehcache.jar - hibernate3.jar - jta.jar - dom4j.jar - log4j.jar

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Hibernate Environment Hibernate configuration property file 

Used for configuring hibernate configuration

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Contains - Database Configuration - Datasource Configuration - Transaction Configuration - Caching Configuration - ConnectionPool Configuration - Other Settings.

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Hibernate Environment The hibernate-mapping configuration file 

Object to relation mappings are often defined in a xml file

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Easy mapping file can be hand written or edited.

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Java Centric persistence classes.

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No of tools available to generate the configuration. -AndroMDA -XDoclets -Middlegen

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Standard DTD for correct implementation

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Hibernate Round Trip development Hibernate Configuration

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Hibernate Round Trip development Employee Java Object

“Employee” DB Table

Column

|

Type

| Modifiers

----------+-----------------------+--------EMPID (PK) |

int

| not null

name

|

varchar(50)

| not null

salary

|

double

|

email

|

varchar(50)

|

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Hibernate Round Trip development 

Hibernate XML Configuration Employee.hbm.xml

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Hibernate Round Trip development    

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

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Employee emp = new Employee() emp.setEmail(“[email protected]”); emp.setName(“Gopal Patel”); emp.setSalary(“121”); session.save(emp); Tx.commit(); session.close();

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Hibernate Round Trip development 

Loading the Employee

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Try{

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

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Employee emp = session.get(Employee.Class, new Long(1)); System.out.println(“Employee salary : ” + emp.getSalary()); Tx.commit(); }Catch(HibernateException e){ e.printStackTrace(); } CONFIDENTIAL

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Features of Hibernate            

Persistence for POJOs (JavaBeans) Flexible and intuitive mapping Support for fine-grained object models Powerful, high performance queries Dual-Layer Caching Architecture (HDLCA) Toolset for roundtrip development Support for detached objects (no DTOs) Automatic Dirty Checking Transitive Persistence Lazy Fetching Outer Join Fetching Runtime SQL Generation

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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 CONFIDENTIAL

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Tools Support 

XDoclet 

Modeling tools / Code generator   

Middlegen AndroMDA IDE Plug-in support:  Eclipse, IDEA

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Hibernate References   

Http://hibernate.org Hibernate in Action (Manning, 2004) Tool support   

http://xdoclet.sf.net http://boss.bekk.no/boss/middlegen http://www.andromda.org/

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Important points to remember 

Project uses RDBMS ? Need to have well-designed strategy to persistent objects.  

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The application performance considering data retrieval Simplicity in terms of coding

It maps the database tables same as their relations between each other – which we call domain models / POJO configuration file (hibernate.cfg.xml) mapping file and POJO Transaction, Connection Pooling, CRUD etc…

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Thank You 

Mail: [email protected]

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