Hibernate
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Hibernate is an open source ORM tool that provides transparent persistence for Java objects (POJOs). It maps Java objects to relational database tables without requiring the developer to write SQL code. Hibernate uses an object-oriented domain model and handles the conversion between the domain model and the relational data. It supports common object-oriented features like inheritance, polymorphism, and associations. Hibernate provides data query, caching, transactions, and connection pooling to simplify data access for Java applications.
Hibernate
- 1. CONTENTS 1. Overview 2. Advantages over JDBC 3. Hibernate Architecture 4. Downloading and Installing Hibernate
- 2. Overview • A popular open source Object Relational Mapping(ORM) tool which provides transparent persistence for POJOS. • ORM is used to map objects to relational databases(Oracle,Mysql). • Allows to map java objects to relational databases and also provides data query • Generates the SQL calls and makes application portable to all SQL databases, with database portability • Allows to develop persistent classes with all java terms – like association, inheritance, polymorphism etc • Can be used as in standalone Java applications or as in Java EE applications using servlets or EJB session beans.
- 3. Advantages of Hibernate • Retains natural object model (transparent) • Minimizes Code • Does not require a container • Model is not tied to persistence implementation. • Metadata controlled persistence • Transparent - working with the model, not the data access technology • Pooling, Caching, Transactions can be handled outside of our code • Object/relational mappings are defined in an XML document. The mapping document is designed to be readable and hand-editable. • Mapping language is Java-centric, meaning that mappings are constructed around persistent class declarations, not table declarations. • Choose to define XML mappings by hand, or by using tools like XDoclet, Middlegen and AndroMDA.
- 6. • The “Lite" architecture has the application provide its own JDBC connections and manage its own transactions • Has – SessionFactory – Session – Persistent Objects – Transient Objects • The "full cream" architecture abstracts the application away from the underlying JDBC and Java Transaction API (JTA) and lets Hibernate take care of the details
- 8. Configuration Configuration class's operation has two key components: • The database connection – handled through one or more configuration files supported by Hibernate – hibernate.properties and hibernate.cfg.xml • The classmapping setup – makes the connection between the Java classes and database tables.
- 9. hibernate.cfg.xml <?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" "http://hibernate.sourceforge.net/hibernate-configuration- 2.0.dtd"> <hibernate-configuration> <session-factory> <property name="connection.driver"> com.mysql.jdbc.Driver </property> <property name="connection.url“> jdbc:mysql://localhost/products </property> <property name="dialect"> net.sf.hibernate.dialect.MySQLDialect </property> </session-factory> </hibernate-configuration>
- 10. hibernate.properties hibernate.dialect net.sf.hibernate.dialect.MySQLDialect hibernate.connection.driver_class com.mysql.jdbc.Driver hibernate.connection.url jdbc:mysql://localhost/products hibernate.connection.username root hibernate.connection.password root hibernate.show_sql true hibernate.cglib.use_reflection_optimizer false
- 11. Hibernate 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> <class name="Notes“ table="notes"> <id name="id" unsaved-value="0"> <generator class="native"/></id> <property name="info" type="string"/> <property name="count" type="integer" not-null="true"/> <property name="zipcode" type="string"/> <property name="fullname" type="string"/> </class></hibernate-mapping>
- 12. Hibernate Architecture • Basic interfaces used while working with Hibernate are: - SessionFactory - Session - Transaction
- 13. SessionFactory • A singleton class called SessionFactory is instantiated. • A threadsafe, immutable cache of compiled mappings for a single database. • The SessionFactory object is heavyweight; better to create only one SessionFactory per application. • A factory for creating session objects • Can hold an optional(second-level) cache of data that is reusable between transactions at a process
- 14. Session • A single-threaded, short-lived object representing a conversation between the application and the persistent store. • is lightweight and instantiated each time an interaction is needed with the database. • As the Session object is created, the objects are persisted or loaded from the database • Then the session object is flushed and closed. • It wraps a JDBC connection and is a factory for Transaction. • Opened by SessionFactory.openSession() • Closed by session.close()
- 15. ThreadLocal Session Pattern • Use ThreadLocal variable to maintain session data ThreadLocal • Specialized Java class which is associated to a user thread of execution and serves as a data container throughout the lifespan of the thread (or child threads) • Global variable which is local for every thread • To create a thread ThreadLocal sess = new ThreadLocal(); Session session = sess.get(); // to get the current session
- 16. Transaction • A single-threaded, short-lived object used by the application to specify atomic units of work. • It abstracts the application from the underlying JDBC, JTA or CORBA transaction. • A Session might span several Transactions in some cases. is connected with a concrete session Transaction tx = session.beginTransaction( );
- 17. Persistent objects and collections(Entities) • Short-lived, single threaded objects containing persistent state and business function. • Can be ordinary JavaBeans/POJOs. • associated with exactly one Session. Transient and detached objects and collections • Instances of persistent classes that are not currently associated with a Session. • Might have been instantiated by the application and not yet persisted • Might have been instantiated by a closed Session.
- 18. Hibernate Callbacks • public Boolean onSave(Session s); - called before the object is saved to the • database • public Boolean onUpdate(Session s); - called before the object is updated • public boolean onDelete(Session s); - called before the object is deleted • public Boolean onLoad(Session s); - called after the object is loaded from • the database
- 19. Downloading and Installing Downloading • Download Hibernate from the site (ie) from JBoss tools as Zip • Extract the files to your preferred location • Has 2 folders – plugins and features Adding to Eclipse • Add the files within hibernate /features folder to eclipse/features folder • Add the files within hibernate /plugins folder to eclipse/plugins folder Alternate Way • Open eclipse Help Update site add hibernate from site
Editor's Notes
- #4: Dirty checking Hibernate allows dirty checking feature.All persistent objects are monitored by hibernate.it detects which objects have been modified and then calls update statements on all updated objects.the process of updating the changed object is called automatic dirty checking. Dirty checking allows the user or developer to avoid the time consuming databases write actions. This feature makes necessary updations and changes to the fields which require a change, remaining fields are left unchanged or untouched.