In this example we are describing one-to-many relation. There are two table one is Faculty and other is Subject.

Faculty Table    

Facultyi_Id Faculty_Name
1 Neelesh
2 Remu
3 Kripa

                                   

   Subject Table

Subject_Id Subject_Name
1 c
2 c++
3 Java
4 VB
5 Dotnet

 

Bridge Table i.e  Facult_Subject

Faculty_Id

Subject_Id

1 1
1 2
2 3
2 4
2 5

 


In a College  suppose different subjects can assign to one faculty but that same subject can't assign to different faculty. This is an one-to-many relationship.  In this example we have shown facuty_id no 1 has assigned two subjects i.e  c and c++, faculty_id no 2 - one subject java and so on. The Bridge table contains  Faculty_id and Subject_id. This can be achieve by many-to-many mapping but we have to add one more attribute i,e unique="true"


TO achiving this relation we have to follow these steps

Step1: Create  Faculty and Subject class

Faculty.java


package com.bullraider.onetomany;
import java.util.HashSet;
import java.util.Set;
public class Faculty {
    private long id;
    private String name;
        private Set<Subject> subjects=new HashSet<Subject>(0);
        public Faculty(String name) {
        super();
        this.name = name;
       
    }
    public Set<Subject> getSubjects() {
        return subjects;
    }
    public void setSubjects(Set<Subject> subjects) {
        this.subjects = subjects;
    }
    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

}




Subject.java

package com.bullraider.onetomany;
public class Subject {
    private long id;
    private String name;
    public Subject(String name) {
        super();
        this.name = name;
    }

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



Step2: Create Faculty.hbm.xml and Subject.hb.xml

Faculty.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.bullraider.onetomany.Faculty" table="Faculty">
        <meta attribute="class-description"> This class contains Faculties details. </meta>
        <id name="id" type="long" column="id">
            <generator class="native" />
        </id>
        <property name="name" type="string" not-null="true" />
                        <set name="subjects" table="subject_faculty" cascade="all" >
            <key column="faculty_Id" />
            <many-to-many column="subject_Id" class="com.bullraider.onetomany.Subject" unique="true"/>
        </set>
    </class>
</hibernate-mapping>

Subject.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.bullraider.onetomany.Subject" table="subject">
        <meta attribute="class-description"> This class contains policy details. </meta>
        <id name="id" type="long" column="id">
            <generator class="native" />
        </id>
        <property name="name" type="string" not-null="true" />
        </class>
</hibernate-mapping>

Step3: Create Configuration file

<?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="hibernate.connection.driver_class">oracle.jdbc.OracleDriver</property>
        <property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:ORCL</property>
        <property name="hibernate.connection.username">scott</property>
        <property name="connection.password">tiger</property>
        <property name="connection.pool_size">1</property>
        <property name="hibernate.dialect">org.hibernate.dialect.OracleDialect</property>
        <property name="show_sql">true</property>
       <property name="hbm2ddl.auto">create-drop</property>
              <mapping resource="com/bullraider/manytomany/Subject.hbm.xml"/>
        <mapping resource="com/bullraider/manytomany/Faculty.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

step4: Create HibernateUtil class to get SessionFactory Object

package com.bullraider.manytomany;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
    private static final SessionFactory sessionFactory;
    static {
        try {
            sessionFactory = new Configuration().configure()
                    .buildSessionFactory();
        } catch (Throwable ex) {
            System.err.println("SessionFactory creation failed" + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}


step5: Create One Main Class for adding opertions.

package com.bullraider.onetomany;
import java.util.HashSet;
import java.util.Set;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.bullraider.onetomany.util.HibernateUtil;
public class Main {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = null;
        try {
            transaction = session.beginTransaction();
            Set<Subject> subject= new HashSet<Subject>();
            subject.add(new Subject("Java"));
            subject.add(new Subject("C++"));
            Faculty fc1=new Faculty("Srinivas");
            fc1.setSubjects(subject);
            session.save(fc1);
            transaction.commit();
            System.out.println("Records inserted sucessessfully");
        } catch (HibernateException e) {
            transaction.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }

    }
}

Note:

 

<set name="subjects" table="subject_faculty" cascade="all" >
            <key column="faculty_Id" />
            <many-to-many column="subject_Id" class="com.bullraider.o2m.Subject" unique="true"/>
        </set>

Here we are creating Bridge table "subject_faculty" having attribute "faculty_Id" ,"subject_Id.

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