Mapping & Configuration file in hibernate

Mapping Xml file:-
An Object/relational mappings are usually defined in an XML document. This mapping file instructs Hibernate — how to map the defined class or classes to the database tables?

Syntax Of Mapping xml:-

<hibernate-mapping>

<class name="POJO class name" table="table name in database">

<id name="variable name" column="column name in database" type="java/hibernate type" />

<property name="variable1 name" column="column name in database" type="java/hibernate type" />

<property name="variable2 name" column="column name in database" type="java/hibernate type" />

</class>

</hibernate-mapping>

Configuration:-

Configuration is the file loaded into an hibernate application when working with hibernate, this configuration file contains 3 types of information..

• Connection Properties 
• Hibernate Properties 
• Mapping file name(s)

We must create one configuration file for each database we are going to use, suppose if we want to connect with 2 databases, like Oracle, MySql, then we must create 2 configuration files.

  No. of databases we are using  = That many number of configuration files  

Syntax Of Configuration xml:

<hibernate-configuration>

<session-factory>

<!-- Related to the connection START -->

<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>

<!-- Related to the connection END -->

<!-- Related to hibernate properties START -->

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

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

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

<!-- Related to hibernate properties END-->

<!-- Related to mapping START-->

<mapping resource="hbm file 1 name .xml" / >

<mapping resource="hbm file 2 name .xml" / >

<!-- Related to the mapping END -->

</session-factory>

</hibernate-configuration>

Let see one example to get more clarity about mapping and configuration file in hibernate..

•  write pojo class whose objects will persist in the table..

public class Employee {

   private int id;

   private String firstName;

   private String lastName;  

   private int salary; 

   public Employee() {}

  

   public Employee(String fname, String lname, int salary) {

      this.firstName = fname;

      this.lastName = lname;

      this.salary = salary;

   }

  

   public int getId() {

      return id;

   }

  

   public void setId( int id ) {

      this.id = id;

   }

  

   public String getFirstName() {

      return firstName;

   }

  

   public void setFirstName( String first_name ) {

      this.firstName = first_name;

   }

  

   public String getLastName() {

      return lastName;

   }

  

   public void setLastName( String last_name ) {

      this.lastName = last_name;

   }

  

   public int getSalary() {

      return salary;

   }

  

   public void setSalary( int salary ) {

      this.salary = salary;

   }

}

• create a table in pojo class data will be persist.

create table EMPLOYEE (

   id INT NOT NULL auto_increment,

   first_name VARCHAR(20) default NULL,

   last_name  VARCHAR(20) default NULL,

   salary     INT  default NULL,

   PRIMARY KEY (id)

);

• Write a maping file of your pojo class.

<?xml version = "1.0" encoding = "utf-8"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

   <class name = "Employee" table = "EMPLOYEE">

     

      <meta attribute = "class-description">

         This class contains the employee detail.

      </meta>

     

      <id name = "id" type = "int" column = "id">

         <generator class="native"/>

      </id>

     

      <property name = "firstName" column = "first_name" type = "string"/>

      <property name = "lastName" column = "last_name" type = "string"/>

      <property name = "salary" column = "salary" type = "int"/>

     

   </class>

</hibernate-mapping>

• Write a configuration file for the pojo class

<?xml version = "1.0" encoding = "utf-8"?>

<!DOCTYPE hibernate-configuration SYSTEM

"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

   <session-factory>

  

      <property name = "hibernate.dialect">

         org.hibernate.dialect.MySQLDialect

      </property>

     

      <property name = "hibernate.connection.driver_class">

         com.mysql.jdbc.Driver

      </property>

     

      <!-- Assume test is the database name -->

     

      <property name = "hibernate.connection.url">

         jdbc:mysql://localhost/test

      </property>

     

      <property name = "hibernate.connection.username">

         root

      </property>

     

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

         root123

      </property>

     

      <!-- List of XML mapping files -->

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

     

   </session-factory>

</hibernate-configuration>