Hibernate is an object-relational mapping tool for Java. It uses configuration and mapping files to establish connections to a database and map Java classes and their properties to database tables and columns. The main Hibernate objects are the Configuration, which reads configuration files; the SessionFactory, which is a factory for Session objects; and the Session, which provides the interface to work with the database and manage transactions using Transaction objects. Hibernate uses object-relational mapping to convert between object-oriented and relational structures.

1. Hibernate

2. Content covered
• Introduction to Hibernate
• Hibernate Architecture
• O/R Mapping in Hibernate

3. Hibernate Architecture

4. Configuration
(org.hibernate.cfg.Configuration)
• The Configuration object, as seen in the
example code, is the first Hibernate object you
use. It represents a configuration or properties
file for Hibernate. The Configuration object is
usually created once during application
initialization.
• The Configuration object reads and establishes
the properties Hibernate uses to get connected
to a database and configure itself for work. A
Configuration object is used to create a
SessionFactory and then typically is discarded.

5. Example
<?xml version="1.0" encoding="UTF-8"?>
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class"> org.hsqldb.jdbcDriver
</property>
<property name="hibernate.connection.url">jdbc:hsqldb:hsql://localhost
</property>
<property name="hibernate.connection.username">sa</property>
<property name="connection.password"></property>
<property name="connection.pool_size">1</property>
<property name="hibernate.dialect"> org.hibernate.dialect.HSQLDialect
</property>
<mapping resource="com/vaannila/student/Student.hbm.xml"/>
<mapping resource="com/vaannila/student/Address.hbm.xml"/>
</session-factory>
</hibernate-configuration>

6. SessionFactory
(org.hibernate.SessionFactory)
• Created from a Configuration object, and
as its name implies it is a factory for
Session objects.
• An expensive object to create. It, like the
Configuration object, is usually created
during application start up. However,
unlike the Configuration object, It should
be created once and kept for later use.

7. SessionFactory
• SessionFactory object,
– used by all the threads of an application. It is
a thread safe object.
– One SessionFactory object is created per
database.
– Multiple SessionFactory objects (each
requiring a separate Configuration) are
created when connecting to multiple
databases.

8. Hibernate Flow of Work

9. Session
(org.hibernate.Session)
• Provide the main interface to accomplish work with the
database. Persistent objects are saved
and retrieved through a Session object.
• Lightweight & inexpensive to create, does the work of
getting a physical connection to the database.
• Not thread safe. Therefore, session objects should not
be kept open for a long time.
• Applications create and destroy these as needed.
• When modifications are made to the database, Session
objects create a Transaction object.

10. Transaction
(org.hibernate.Transaction)
• Represents a unit of work with the database
(and potentially other systems). Transactions in
Hibernate are handled by an underlying
transaction manager and transaction (from
JDBC, JTA or CORBA).
• Abstracts the developer from having to deal with
the underlying transaction manager/transaction.
• Transaction objects should be kept open for as
short of time as
possible.

11. Example
Sessionsession=
SessionFactory.newSession();
Transaction tx = session.beginTransaction( );
tx.commit(); tx.rollback();
session.close()

12. Query & Criteria
• Both objects are used to retrieve (and
recreate) persistent objects.
• Query objects use SQL or Hibernate
Query Language (HQL) string to retrieve
data from the database & create objects.
• Criteria enables developer to create and
execute the object-oriented criteria
queries.

13. Hibernate O/R Mapping
• ORM is a technique to map object-
oriented data with the relational data.
• Used to convert datatype supported in
object-oriented programming language to
a datatype to a data type supported by a
database. (if mapping is not provided,
exception is thrown while transferring an
object oriented data to the database)

14. Hibernate O/R Mapping
• Mapping in the format that relate
– Classes with tables.
– Properties with columns
– SQL types with Java types.
• O/R Mapping can be written for any
database that can be oracle, DB2, MySql,
Sybase.

15. Hibernate O/R Mapping
• xml file
XML mapping documents allows you to:
– Bridge the gap between object-oriented
systems and relational databases
– Define the object-relational mapping
– Help to generate and export database table

16. Associations strategies
• Mainly 3 Association strategies available
in O/R mapping:
• 1. One-2-one
• 2. One-2-many
• 3. Many-2-one
• 4. Many-2-many

17. Hibernate Mapping files
<?xml version="1.0"?>
<hibernate-mapping>
<class name="com.vaannila.student.Student" table="STUDENT">
<id name="studentId" type="long" column="STUDENT_ID">
<generator class="native“/></id>
<property name="studentName" type="string" not-null="true"
length="100" column="STUDENT_NAME" />
<many-to-one name="studentAddress"
class="com.vaannila.student.Address"
column="STUDENT_ADDRESS" not-null="true" cascade="all"
unique="true" />
</class>
</hibernate-mapping>