HIBERNATE 4U: Hibernate Mapping One-to-Many using Annotations

In this example you will learn how to map one-to-many relationship using Hibernate Annotations. Consider the following relationship between Student and Phone entity.

According to the relationship a student can have any number of phone numbers.
To create this relationship you need to have a STUDENT, PHONE and STUDENT_PHONE table. The relational model is shown below.

To create the STUDENT and PHONE table you need to create the following Java Class files.
Student class is used to create the STUDENT and STUDENT_PHONE table.

package com.vaannila.student;
 
import java.util.HashSet;
import java.util.Set;
 
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.OneToMany;
import javax.persistence.Table;
 
@Entity
@Table(name = "STUDENT")
public  class Student {
 
    private long  studentId;
    private String  studentName;
    private Set  studentPhoneNumbers = new HashSet(0);
 
    public Student()  {
    }
 
    public Student(String  studentName, Set studentPhoneNumbers) {
        this.studentName  = studentName;
        this.studentPhoneNumbers =  studentPhoneNumbers;
    }
 
    @Id
    @GeneratedValue
    @Column(name  = "STUDENT_ID")
    public long  getStudentId() {
        return this.studentId;
    }
 
    public void  setStudentId(long  studentId) {
        this.studentId  = studentId;
    }
 
    @Column(name  = "STUDENT_NAME",  nullable = false,  length = 100)
    public String  getStudentName() {
        return this.studentName;
    }
 
    public void  setStudentName(String studentName) {
        this.studentName  = studentName;
    }
 
    @OneToMany(cascade  = CascadeType.ALL)
    @JoinTable(name = "STUDENT_PHONE", joinColumns =  { @JoinColumn(name  = "STUDENT_ID")  }, inverseJoinColumns = { @JoinColumn(name = "PHONE_ID") })
    public Set  getStudentPhoneNumbers() {
        return this.studentPhoneNumbers;
    }
 
    public void  setStudentPhoneNumbers(Set  studentPhoneNumbers) {
        this.studentPhoneNumbers =  studentPhoneNumbers;
    }
 
}

The @OneToMany annotation is used to create the one-to-many relationship between the Student and Phone entities. The @JoinTable annotation is used to create the STUDENT_PHONE link table and @JoinColumn annotation is used to refer the linking columns in both the tables.
Phone class is used to create the PHONE table.

package com.vaannila.student;
 
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
 
@Entity
@Table(name = "PHONE")
public  class Phone {
 
    private long  phoneId;
    private String  phoneType;
    private String phoneNumber;
 
    public Phone()  {
    }
 
    public Phone(String  phoneType, String phoneNumber) {
        this.phoneType  = phoneType;
        this.phoneNumber =  phoneNumber;
    }
     
    @Id
    @GeneratedValue
    @Column(name  = "PHONE_ID")
    public long  getPhoneId() {
        return this.phoneId;
    }
 
    public void  setPhoneId(long  phoneId) {
        this.phoneId  = phoneId;
    }
 
    @Column(name  = "PHONE_TYPE",  nullable = false,  length=10)
    public String  getPhoneType() {
        return this.phoneType;
    }
 
    public void  setPhoneType(String phoneType) {
        this.phoneType  = phoneType;
    }
     
    @Column(name  = "PHONE_NUMBER",  nullable = false,  length=15)
    public String  getPhoneNumber() {
        return this.phoneNumber;
    }
 
    public void  setPhoneNumber(String phoneNumber) {
        this.phoneNumber  = phoneNumber;
    }
 
}

Now create the hibernate configuration file with the Student and Phone class mapping.

"1.0" encoding="UTF-8"?>

        "-//Hibernate/Hibernate  Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

    
        "hibernate.connection.driver_class"> org.hsqldb.jdbcDriver
        "hibernate.connection.url">  jdbc:hsqldb:hsql://localhost
        "hibernate.connection.username">sa
        "connection.password">
        "connection.pool_size">1
        "hibernate.dialect">  org.hibernate.dialect.HSQLDialect
        "show_sql">true
        "hbm2ddl.auto">create-drop
        class="com.vaannila.student.Student" />
        class="com.vaannila.student.Phone" />
    


Create the Main class to run the example.

package com.vaannila.student;
 
import java.util.HashSet;
import java.util.Set;
 
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
 
import com.vaannila.util.HibernateUtil;
 
public class Main {
 
    public static  void main(String[]  args) {
        Session session =  HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = null;
        try {
            transaction =  session.beginTransaction();
             
            Set  phoneNumbers = new HashSet();
            phoneNumbers.add(new Phone("house","32354353"));
            phoneNumbers.add(new Phone("mobile","9889343423"));
             
            Student  student = new Student("Eswar", phoneNumbers);
            session.save(student);
             
            transaction.commit();
        } catch  (HibernateException e) {
            transaction.rollback();
            e.printStackTrace();
        } finally  {
            session.close();
        }
 
    }
 
}