HibernateForDummies

Simple Hibernate project

Hibernate :

• ORM framework which means .. Object (Java application) -> Relational (Database) Mapping.
• Traditional JDBC applications doesnt support object mapping and hence we store as text but hibernate eliminates it by introducing orm
• In JDBC user needs to handle exceptions as they are all checked but hibernate has unchecked excpetions
• In JDBC we write sql commands everywhere so if the table structure changes, we need to modify at every place
• Hibernate provides HQL which is databse independent
• If we save derived class obj in hibernate then base class object also gets saved.
• Primary keys can be generated automatically by hibernate
• Hibernate provides caching to improve performance by reducing no.of calls between app and db
• Pagination based querying is quite simple in hibernate

== Steps involved in interacting with db using hibernate ==

1. Load configuration. { either configuration file or props file }
2. Obtain SessionFactory instance { configuration.buildSessionFactory() }
3. Open Session using sessionFactory instance.

Configuration :

• 2 ways to configure : properties file and XML. XML is preferred.
• Configuration file consists of connection properties, mapping config, db behavorial properties etc.

Mapping and configuration are the heart for any hibernate application.

• Mapping is generally taken through Annotations / XML. There can be multiple mapping files { no. of POJO's=no. of mapping files}
• Using annotations is more simpler. Mapping config contains the mapping between java object and database columns which tells hibernate which kind of value to be stored in the db.
• Mapping config is then attached in configuration file. Configuration file is generally XML, older versions properties file is also used for this purpose but xml is preferred.

-- This example is about company consisting of employees and departments. We are using xml file for hibernate configuration and annotations for orm