Hibernate

Hibernate

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  Introduction to Hibernate SujitKumar Zenolocity LLC Copyright 2012-2024 @
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  What is Hibernate? •Hiberate => pure java ORM tool, ORM => Object Relational Mapping tool. Examples of ORM: Hibernate, Kodo, etc. • Persist java objects to tables in a relational database. • Java API for performing basic CRUD operations (CRUD is create, read, update and delete) • Java API to express queries referring to java objects • Java API to specify metadata • Optimization facilities : lazy loading, dirty checking
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  Why we needHibernate? • Improved productivity – High-level object-oriented java API – Less Java code to write – No SQL to write • Improved performance – Sophisticated caching – Lazy loading – Eager loading • Improved maintainability – Less code to write • Improved portability – ORM framework generates database-specific SQL for you. Will work with different databases like Oracle, MySQL, Sybase, etc.
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  How of Hibernate? •Map POJOs (plain old Java objects) to relational database tables using (XML) configuration files called Hibernate Mapping Files (*.hbm)
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  Hibernate Mapping Files •Maps java classes to database tables. • Maps java class attributes to the columns of a table in an RDBMS. • Map relationships (1 to 1, 1 to many or many to many) between java classes and tables.
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  Hibernate Configuration Two Options: •Declarative via XML configuration in a file called hibernate.cfg.xml • Programmatic
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  hibernate.cfg.xml file Configure thesession factory with following: • JDBC Connection configuration • SQL variant to generate (Oracle / MySQL /…) • Connection pool configuration • List of mapping files which maps each java class to a table in the database. • Optional - create database schema from the mapping files
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  Core Interfaces • • • • • SessionFactory interface Sessioninterface Configuration interface Transaction interface Query and Criteria interfaces
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  SessionFactory interface • Theapplication obtains Session instances from a SessionFactory. • Generally, there is a single SessionFactory for the whole application and it is created during application initialization. • The SessionFactory caches generated SQL statements and other mapping metadata that Hibernate uses at runtime. • Holds cached data that has been read in one transaction and may be reused in a future transaction. SessionFactory sessionFactory = configuration.buildSessionFactory();
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  Session Interface • Maininterface used by Hibernate applications. • Single-threaded, short-lived object representing a conversation between the application and the persistent store. • Can be used to create query objects to retrieve persistent objects. Session session = sessionFactory.openSession(); • Wraps a JDBC connection • Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier
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  Usage • Load theHibernate configuration file and create configuration object. It will automatically load all hibernate mapping files (*.hbm) • Create session factory from configuration object • Get a session from this session factory • Create HQL Query • Execute queries which map rows in a database table to java objects
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  HQL • Object orientedextension to SQL • Like SQL, it can create, save, update and delete data in a persistent store.