Hibernate Basics

Hibernate Basics:

Today I am going to discuss on basic hibernate example:

Basic files required to work with hibernate:

1. POJO class.

2. Hibernate mapping file

3. Hibernate configuration file

4. Client application

1. POJO class:

If a class is not extending any pre-defined class or not implementing any pre-defined interface given by API, such type of  classes are called POJO class.

Example:

Class Student

{
private String  StudentName;

Private int StudentNumber;

----

//setters and getters for above variables

}

2. Hibernate mapping file:

Hibernate mapping file is an XML file, which contains association between POJO class name  to database table name and POJO class member variables to database table column names. Mapping file name we  to give as <anyname>.hbm.xml, here hbm is to identify the file is hibernate mapping file. We can give any name .xml file, but it is not recommended to use <anyname>.hbm.xml.

Example

1. Student.xml

2. Student.hbm.xml

1^st & 2^nd  correct but 2^nd  one is recommended

Student.hbm.xml

<! DTD is must and should>

<hibernate-mapping>

<calss name=”Student” table=”STUDENT”>

<id name=”studentId” column =”sid”>

<generator class=”assigned”/>

</id>

<property name=”studentName” column name=”SNAME”>

<property name=”studentNumber” column name=”SNO”>

</class>

</hibernate-mapping>

3. Configuration file

Hibernate need some additional properties along with mapping file, in order to transfer the objects between java application and database.

In configuration file we will add the following information.

1. connection properties-hibernate will establish connection with database

2. hibernate properties-adding additional information about database

3. mapping resources-include hibernate mapping file in hibernate configuration file.

When hibernate configuration file is loaded automatically hibernate mapping file will also load.Hibernate configuration file is  identified with <any-name>.cfg.xml file. Here cfg specifies it is hibernate configuration file.

<any-name>.cfg.xml

<!DTD must>

<hibernate-configuration>

<session-factory>

<!- -connection properties-->

<property name="connection.driver_class">Driver Class Name </property>

<property name="connection.url">URL </property>

<property name="connection.user">user </property>

<property name="connection.password">password</property>

<!- -hibernate properties-->

<property name="hibernate.show_sql">true/false</property>

<property name="hibernate.dialet">Database dialet class</property>

<property name=" hibernate.hbm2ddl.auto">create/update or what ever</property>

<!- -mapping resources-->

<mapping resource="hbm file1 .xml" / >

<mapping resource=" hbm file2.xml" / >

</session-factory>

</hibernate-configuration>

For each database we have to create separate configuration file, i.e if we have 3 databases we need to create 3 hibernate configuration files.

4. Client application

Step1: Import the hibernate API in to client application.

Import org.hibernate.*;

Import org.hibernate.cfg.*;

Step2:

Create an object for Configuration class, by creating an object for  Configuration class we are boot strapping hibernate environment into  a java application.

Configuration cfg=new Configuration();

Step 3:

Call configure() method of configuration class, for loading hibernate configuration class.

If the hibernate configuration  file name  is hibernate.cfg.xml then the file name is optional. When configure() method is called  then hibernate internally uses DOM and SAX parsers to read both configuration and mapping file and stores that data in the form of instance variables of the configuration class.

Step 4:

Create high level object of  hibernate called SessionFactory. To get SessionFactory object  we need to call buildSessionFactory() method of configuration class.

SessionFactory factory=cfg. buildSessionFactory();

Step 5:

1. Create or get Session object.

2. SessionFactory produces Sessions and Session is the runtime interface between a java application and hibernate frame work.

3. all methods to perform operations on data base are provided by Session object.

Session session=factory.OpenSession();

Step 6:

Begin or open a logic for transaction, while performing  select ,update,delete operations  from a java application  to a DB, in hibernate we need transaction.if we are loading or reading data from the database we don’t require transaction. To get transaction in hibernate  we need to call beginTransaction()  given by Session interface.

Transaction tx=Session.beginTransaction();

Step 7:

Perform the operations on the database  while using the methods  of Session interface.

Session.save(obj);

Session.update(obj);

Session.delete(obj);

Step 8:

Commit the transaction

Tx.commit();

Step 9:

Close the session and session factory objects.

Session.close();

Factory.close();