Join in Hibernate Example, Hibernate Relationship using One to Many and Many to one

 Join in Hibernate:-

Join is used to merge the columns, in the case of Hibernate we will create a relationship or mapping concept to perform the join operation:-

Type of relationship or association

One to Many -->  One dept has multiple employees

Many to One ---> Multiple employees belonging from Single dept

Many to Many ---> Multiple Employee belonging from Multiple Dept.

One to One  ------->  One Dept to one Employee

Example of Join Syntax:-

Implement Many to one using Two Different Entity Class Dept and Employee:-

Code of Dept Class:-

package scs;

import java.util.Set;

import javax.persistence.*;

@Entity

@Table(name="tbl_dept")

public class Dept {

@Id

private int deptid;

@Column

private String deptname;

public int getDeptid() {

return deptid;

}

public void setDeptid(int deptid) {

this.deptid = deptid;

}

public String getDeptname() {

return deptname;

}

public void setDeptname(String deptname) {

this.deptname = deptname;

}

}

Code of Employee Class:-

package scs;

import javax.persistence.*;

@Entity

@Table(name="tbl_emp")

public class Employee {

@Id

private int empid;

@Column

private String empname;

@ManyToOne(cascade = CascadeType.ALL)

@JoinColumn(name="deptid",referencedColumnName="deptid")

private Dept dept;

public int getEmpid() {

return empid;

}

public Dept getDept() {

return dept;

}

public void setDept(Dept dept) {

this.dept = dept;

}

public void setEmpid(int empid) {

this.empid = empid;

}

public String getEmpname() {

return empname;

}

public void setEmpname(String empname) {

this.empname = empname;

}

}

hiebernate.cfg.xml

<!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">com.mysql.jdbc.Driver</property>

<property name="connection.url">jdbc:mysql://localhost:3306/java5batch</property>

<property name="connection.username">root</property>

<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">create</property>

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

 <mapping class="scs.Dept"></mapping>

 <mapping class="scs.Employee"></mapping>

</session-factory>

</hibernate-configuration>

Code of ManytoOneExample.java:-

package scs;

import java.util.HashSet;

import java.util.Set;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.AnnotationConfiguration;

import org.hibernate.cfg.Configuration;

public class ManytoOneExample {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml"); 

SessionFactory sf = new AnnotationConfiguration().configure().buildSessionFactory();

Session s = sf.openSession();

Dept d = new Dept();

d.setDeptid(20);

d.setDeptname("CS");

Employee em = new Employee();

em.setEmpid(1001);

em.setEmpname("SSS");

em.setDept(d);

Employee em1 = new Employee();

em1.setEmpid(1002);

em1.setEmpname("DDD");

em1.setDept(d);

    Transaction tx = s.beginTransaction();

    s.save(em);

    s.save(em1);

    tx.commit();

    s.close();

    sf.close();

}

}

Example to one to many :-

1)  Create Dept.java Master class:-

package scs;

import java.util.Set;

import javax.persistence.*;

@Entity

@Table(name="tbl_dept")

public class Dept {

@Id

private int deptid;

@Column

private String deptname;

public Set getEmpref() {

return empref;

}

public void setEmpref(Set empref) {

this.empref = empref;

}

@OneToMany(fetch=FetchType.LAZY, targetEntity=Employee.class, cascade=CascadeType.ALL)

@JoinColumn(name = "deptid", referencedColumnName="deptid")

private Set empref;

public int getDeptid() {

return deptid;

}

public void setDeptid(int deptid) {

this.deptid = deptid;

}

public String getDeptname() {

return deptname;

}

public void setDeptname(String deptname) {

this.deptname = deptname;

}

}

2)  Create Employee.Java Class as an Association Class

package scs;

import javax.persistence.*;

@Entity

@Table(name="tbl_emp")

public class Employee {

@Id

private int empid;

@Column

private String empname;

public int getEmpid() {

return empid;

}

public void setEmpid(int empid) {

this.empid = empid;

}

public String getEmpname() {

return empname;

}

public void setEmpname(String empname) {

this.empname = empname;

}

}

3)  Create hibernate.cfg.xml

<!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">com.mysql.jdbc.Driver</property>

<property name="connection.url">jdbc:mysql://localhost:3306/java5batch</property>

<property name="connection.username">root</property>

<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">create</property>

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

 <mapping class="scs.Dept"></mapping>

 <mapping class="scs.Employee"></mapping>

</session-factory>

</hibernate-configuration>

4)  Create OnetoMany.java class:-

package scs;

import java.util.HashSet;

import java.util.Set;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.AnnotationConfiguration;

import org.hibernate.cfg.Configuration;

public class ManytoOneExample {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml"); 

SessionFactory sf = new AnnotationConfiguration().configure().buildSessionFactory();

Session s = sf.openSession();

Dept d = new Dept();

d.setDeptid(10);

d.setDeptname("IT");

Employee em = new Employee();

em.setEmpid(1001);

em.setEmpname("XYZ");

Employee em1 = new Employee();

em1.setEmpid(1002);

em1.setEmpname("ABC");

Set st = new HashSet<>();

st.add(em);

st.add(em1);

    d.setEmpref(st);

    Transaction tx = s.beginTransaction();

    s.save(d);

    tx.commit();

    s.close();

    sf.close();

}

}

Now I am Explaining The Inner Join Example in Dept to Employee

package scs;

import java.util.Iterator;

import java.util.List;

import org.hibernate.Query;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.AnnotationConfiguration;

import org.hibernate.cfg.Configuration;

public class JoinExample {

public static void main(String[] args) {

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml"); 

SessionFactory sf = new AnnotationConfiguration().configure().buildSessionFactory();

Session s = sf.openSession();

Query q = s.createQuery("select d.deptid,d.deptname,e.empid,e.empname from Dept d inner join d.empref e");

List lst = q.list();

Iterator it = lst.iterator();

while(it.hasNext())

{

    Object arr[] = (Object[])it.next();

    System.out.println(arr[0] + " "+ arr[1] + " "+arr[2] + " "+ arr[3]);

}

s.close();

sf.close();

}

}

Vendor

vid
vname
Set childern  ----> store record of child object

Cutsomer
custid
custname
vid(fk)  ----> it will take record which will be exist under master

Syntax of Left Join

select v.vname,v.vid,c.custid,c.custname from Vendor v left join v.children c.

Vendor information will match from Customer

Syntax of Right Join
select v.vname,v.vid,c.custid,c.custname from Vendor v right join v.children c.

Customer information will match from Vendor

Many to one :-

Pojo clas

Vendor:-
vid
vname

Customer
cid
cname
parentObjects

Right Join:-

select v.vname,v.vid,c.cname from Customer c Right Join c.parentObjects;

vendor table info will be matched from Customer Table

Left Join:-
select v.vname,v.vid,c.cname from Customer c Left Join c.parentObjects;

Customer Table info will be matched from Vendor Table

Inner Join:-
select v.vname,v.vid,c.cname from Customer c Inner Join c.parentObjects;

Customer Table Matched Information will be Show from Vendor name.

..................................................
Assignment:-
Project:-
ProjectId
ProjectName
ProjectDesc
...................................................................................................................................................
ProjectAssignment
Developerid
Developername
Projectid

One to many:-

Inner Join

Right Join

Left Join
many to one
Inner Join
Right Join
Left Join


Complete Sample example:-

package mappingser;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.hibernate.*;
import org.hibernate.cfg.*;
import mapping.*;
/**
 * Servlet implementation class ManyToOneSer
 */
@WebServlet("/ManyToOneSer")
public class ManyToOneSer extends HttpServlet {
private static final long serialVersionUID = 1L;
     
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ManyToOneSer() {
        super();
        // TODO Auto-generated constructor stub
    }


protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter out = response.getWriter();
response.setContentType("text/html");
Configuration cfg = new Configuration();
cfg.configure("hibernate.cfg.xml");

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



Query q = session.createQuery("select v.vendroid,v.verndroname,c.customername from Customer c  Inner Join c.parentObjects v");
List lst = q.list();
Iterator it = lst.iterator();
while(it.hasNext())
{
Object arr[] = (Object[]) it.next();
    out.print(arr[0]+" "+arr[1]+" "+arr[2]+"<br>");
}
session.close();
    out.println("One To Many is Done..!!");
    factory.close();

}


}

Many To One Join Example:-

package uao;

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 JoinMappingFile {

public static void main(String[] args) {
Configuration cfg = new Configuration();
cfg.configure("hibernate.cfg.xml");
        SessionFactory sf = cfg.buildSessionFactory();
        Session s =sf.openSession();
    //    Query q = s.createQuery("select v.vid,v.vname,c.customername from Customer c inner join c.parentObjects v");
    //    Query q = s.createQuery("select v.vid,v.vname,c.customername from Customer c left join c.parentObjects v");
        Query q = s.createQuery("select v.vid,v.vname,c.customername from Customer c right join c.parentObjects v");
        List lst = q.list();
        Iterator it = lst.iterator();
        while(it.hasNext())
        {
        Object arr[]=  (Object[])it.next();
        System.out.println(arr[0]+" "+arr[1]+" "+arr[2]);
        }
        s.close();

}

}