What is Hibernate?
• Hibernate is an object-relational mapping tool (ORM) that allows for persisting Java objects in a relational database
• Driven by XML configuration files to configure data connectivity and map classes to database tables
• Not a Java/SQL code generation tool
• Developer writes code to call API
• API executes necessary SQL at runtime
Why Use Hibernate?
• Eliminate need for repetitive SQL
• Work with classes and objects instead of queries and result sets
• More OO, less procedural
• Mapping approach can resist changes in object/data model more easily
• Strong support for caching
• Handles all create-read-update-delete (CRUD) operations using simple API; no SQL
• Generates DDL scripts to create DB schema (tables, constraints, sequences)
• Flexibility to hand-tune SQL and call stored procedures to optimize performance
• Supports over 20 RDBMS; change the database by tweaking configuration files
Plain Old Java Object (POJO)
Default constructor
• Identifier property
• Get/set pairs
• Collection
property is an interface type
Creating Objects
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
AuctionItem item = new AuctionItem();
item.setDescription(”Batman Begins”);
item.setType(”DVD”);
session.save(item);
tx.commit();
session.close();
Updating Objects
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
AuctionItem item =(AuctionItem) session.get(ActionItem.class, itemId);
item.setDescription(newDescription);
tx.commit();
session.close();
Deleting Objects
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
AuctionItem item =(AuctionItem) session.get(ActionItem.class, itemId);
session.delete(item);
tx.commit();
session.close();
Selecting Objects
• Hibernate Query Language (HQL), similar to SQL
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
List allAuctions = session.createQuery(”select item from AuctionItem item
join item.bids bid where item.description like ‘Batman%’
and bid.amount < 15 “).list();
tx.commit();
session.close();
Key Hibernate Classes
• Configuration – uses mapping and database connection metadata to create SessionFactory
• SessionFactory –thread-safe cache of compiled mappings for database; created
once at application startup (expensive)
•– Session – represents a “conversation” between application and database; holds 1st
level cache of objects
• Transaction – an atomic unit of work SessionFactory
• Once the Configuration is prepared, obtaining the SessionFactory is
easy:
Configuration cfg = new Configuration();
// … do some configuration …
cfg.configure();
SessionFactory sf = cfg.buildSessionFactory();
Hibernate Querying Options
• HQL
– Syntax similar to SQL
– Unlike SQL, HQL is still database-agnostic
• Criteria
– Java-based API for building queries
– Good for queries that are built up using lots of conditional logic; avoids messy string manipulation
• SQL / PLSQL
– Often needed to optimize for performance or
leverage vendor-specific features
• Hibernate is an object-relational mapping tool (ORM) that allows for persisting Java objects in a relational database
• Driven by XML configuration files to configure data connectivity and map classes to database tables
• Not a Java/SQL code generation tool
• Developer writes code to call API
• API executes necessary SQL at runtime
Why Use Hibernate?
• Eliminate need for repetitive SQL
• Work with classes and objects instead of queries and result sets
• More OO, less procedural
• Mapping approach can resist changes in object/data model more easily
• Strong support for caching
• Handles all create-read-update-delete (CRUD) operations using simple API; no SQL
• Generates DDL scripts to create DB schema (tables, constraints, sequences)
• Flexibility to hand-tune SQL and call stored procedures to optimize performance
• Supports over 20 RDBMS; change the database by tweaking configuration files
Plain Old Java Object (POJO)
Default constructor
• Identifier property
• Get/set pairs
• Collection
property is an interface type
Creating Objects
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
AuctionItem item = new AuctionItem();
item.setDescription(”Batman Begins”);
item.setType(”DVD”);
session.save(item);
tx.commit();
session.close();
Updating Objects
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
AuctionItem item =(AuctionItem) session.get(ActionItem.class, itemId);
item.setDescription(newDescription);
tx.commit();
session.close();
Deleting Objects
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
AuctionItem item =(AuctionItem) session.get(ActionItem.class, itemId);
session.delete(item);
tx.commit();
session.close();
Selecting Objects
• Hibernate Query Language (HQL), similar to SQL
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
List allAuctions = session.createQuery(”select item from AuctionItem item
join item.bids bid where item.description like ‘Batman%’
and bid.amount < 15 “).list();
tx.commit();
session.close();
Key Hibernate Classes
• Configuration – uses mapping and database connection metadata to create SessionFactory
• SessionFactory –thread-safe cache of compiled mappings for database; created
once at application startup (expensive)
•– Session – represents a “conversation” between application and database; holds 1st
level cache of objects
• Transaction – an atomic unit of work SessionFactory
• Once the Configuration is prepared, obtaining the SessionFactory is
easy:
Configuration cfg = new Configuration();
// … do some configuration …
cfg.configure();
SessionFactory sf = cfg.buildSessionFactory();
Hibernate Querying Options
• HQL
– Syntax similar to SQL
– Unlike SQL, HQL is still database-agnostic
• Criteria
– Java-based API for building queries
– Good for queries that are built up using lots of conditional logic; avoids messy string manipulation
• SQL / PLSQL
– Often needed to optimize for performance or
leverage vendor-specific features
