Hibernate Left Join, Hibernate Left Join Example

Left join means, the objects from both sides of the join are selected and more objects  from left side are selected, even though no equal objects are there at right side, no confusion you will be able to understand if you go through this example i guess 🙂

Let us see an example on hibernate left join, am taking one-to-many to explain this concept files required….

• Vendor.java
• Customer.java
• Vendor.hbm.xml
• Customer.hbm.xml
• hibernate.cfg.xml
• urLogic.java

Vendor.java

package str;

import java.util.Set;

public class Vendor {

	private int vendorId;
	private String vendorName;
	private Set children;

	public int getVendorId() {
		return vendorId;
	}
	public void setVendorId(int vendorId) {
		this.vendorId = vendorId;
	}
	public String getVendorName() {
		return vendorName;
	}
	public void setVendorName(String vendorName) {
		this.vendorName = vendorName;
	}
	public Set getChildren() {
		return children;
	}
	public void setChildren(Set children) {
		this.children = children;
	}

}

Customer.java

package str;
public class Customer {

	private int customerId;
	private String customerName;
	private int forevenId;

	public int getCustomerId() {
		return customerId;
	}
	public void setCustomerId(int customerId) {
		this.customerId = customerId;
	}
	public String getCustomerName() {
		return customerName;
	}
	public void setCustomerName(String customerName) {
		this.customerName = customerName;
	}

	public int getForevenId() {
		return forevenId;
	}
	public void setForevenId(int forevenId) {
		this.forevenId = forevenId;
	}

}

Vendor.xml

<?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="str.Vendor" table="vendor">

<id name="vendorId" column="vendid"  />
<property name="vendorName" column="vendname" length="10"/>

<set name="children" cascade="all" lazy="false">

<key column="forevenid" />
<one-to-many class="str.Customer"/>

</set>

</class>
</hibernate-mapping>

———

Customer.java

<?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="str.Customer" table="customer">

<id name="customerId" column="custid"  />
<property name="customerName" column="custname" length="10"/>

<property name="forevenId" column="forevenid"  insert="false" />

</class>
</hibernate-mapping>

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
<session-factory>
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver
</property>
<property name="connection.url">jdbc:oracle:thin:@www.java4s.com:1521:XE</property>
<property name="connection.username">system</property>
<property name="connection.password">admin</property>

<property name="dialect">org.hibernate.dialect.OracleDialect</property>
<property name="show_sql">true</property>
<property name="hbm2ddl.auto">update</property>

<mapping resource="Customer.hbm.xml"></mapping>
<mapping resource="Vendor.hbm.xml"></mapping>
</session-factory>
</hibernate-configuration>

urLoic.java

package str;

import java.util.Iterator;
import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class urLogic {

	public static void main(String args[])
	{

		Configuration cfg = new Configuration();
		cfg.configure("hibernate.cfg.xml"); 

		SessionFactory factory = cfg.buildSessionFactory();
		Session session = factory.openSession();		

		Query qry= session.createQuery("select v.vendorName, c.customerName from Vendor v Left Join v.children c");

		List l = qry.list();
		Iterator it=l.iterator();

		while(it.hasNext())
		{
			Object rows[] = (Object[])it.next();
			System.out.println(rows[0]+ " -- " +rows[1]);
		}

	}
}

Explanation:

• Actually in urLogic.java see line number 27, i have written select v.vendorName, c.customerName from Vendor v Left Join v.children c
• See before Left Join key word, i selected from Vendor v, after Left Join keywork v.children c
• Means, actually we know in one to many if we select the data from parent then, we will get the data automatically from the children table, i mean records mapping with the parent table, hope you remembered 🙂
• Let in parent we have 5 records, and in children we have 3 records.  And 2 records are having relation with children table records

Before execute this program…..

Out put once we executed……

And thats it mates.., try with Right Join and remaining joins just same concept.

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::. About the Author .::
		Sivateja Kandula - Java/J2EE Full Stack Developer Founder of Java4s - Get It Yourself, A popular Java/J2EE Programming Blog, Love Java and UI frameworks. You can sign-up for the Email Newsletter for your daily dose of Java tutorials.