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How will you create a primary key using Hibernate?

Primary key using Hibernate:

In Hibernate <generator> is used to generate id (primary key)

In the Hibernate the optional <generator> child element names a Java class used to generate unique identifiers for instances of the persistent class
increment generates identifiers of type long, short or int that are unique only when no other process is inserting data into the same table. Do not use in a cluster.

We need to Follow the some setps :

Step 1. create a table name EMPLOYEE in your database


// for MySQL
create table EMPLOYEE (
id bigint(20) ,
name varchar
);
// FOR ORACLE
create table EMPLOYEE (
id number;
name varchar
);

Step 2. Create Emp.java bean class.

Hibernate uses the Plain Old Java Objects (POJOs) classes to map to the database table (Emp.java to EMPLOYEE TABLE). We can configure the variables to map to the database column.

public class Emp {
private long id;
private String name;
public long getId() {
return id;
}
private void setId(long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}

Step 3. Emp.hbm.xml - This mapps EMPLOYEE TABLE and Emp.java : increment for the generator class

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Emp" table="EMPLOYEE">
<id name="id" column="id" type="long">
<generator class="increment"/> // This generates the primary key
</id>
<property name="name" column="name"/>
</class>
</hibernate-mapping>

Step 4.
add Emp.hbm.xml into hibernate.cfg.xml

Hibernate provided connection pooling usning c3p0 and transaction management . Hibernate uses the hibernate.cfg.xml to create the connection pool and setup required environment

<?xml version='1.0' encoding='utf-8'?>
<lt;!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/techfaqdb</property>
<property name="connection.username">techfaq</property>
<property name="connection.password">techfaq</property>
<!-- JDBC connection pool (use the built-in) -->
<property name="hibernate.c3p0.min_size">1</property>
<property name="hibernate.c3p0.max_size">4</property>
<property name="hibernate.c3p0.timeout">1800</property>
<property name="hibernate.c3p0.max_statements">50</property>
<!-- MySQL dialect//different for different Database -->
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>
<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<property name="hbm2ddl.auto">update</property>
<mapping resource="Emp.hbm.xml"/>
</session-factory>
</hibernate-configuration>

Step 5. hibernate automatically increment id using generator

Hibernate Session is the main runtime interface for Hibernate which is used for DataBase operataion. Session has the method like save () , update () , creteQuery() for Data Base operation. You can get session using SessionFactory.openSession() method. SessionFactory allows application to create the Hibernate Sesssion by reading the configuration from hibernate.cfg.xml file. Then the save () method on session object is used to save the contact information to the database.

public class TestExample {
public static void main(String[] args) {
Session session = null;
try{ // This step will read hibernate.cfg.xml
SessionFactory sessionFactory = new
Configuration().configure().buildSessionFactory();
session =sessionFactory.openSession();
System.out.println("Inserting Records");
Emp emp1 = new Emp();
emp1.setName("Nick");
session.save(emp1); // We are Not adding id , hibernate automatically increment the value
Emp emp2 = new Emp();
emp2.setName("Das");
session.save(emp2); // We are Not adding id , hibernate automatically increment the value
session.flush(); // insert data into databse
System.out.println("Save Done- finish database insert");
// Now fetch the Employee data
List empList = session.createQuery("from Emp").list();
//empList contains the list of Employee
for(int i=0;i Emp emp = (Emp)empList.get(i);
System.out.println(emp.getId());
System.out.println(emp.getName());
}
// Out put is : 1 Nick 2 Das
}catch(Exception e){
}finally{
session.close();
}
}
}

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