Hibernate Map mapping

Map in collection:

A map represents an object with key value pair.  A map cannot contain duplicate keys and one key can map to at most one value.

Map mapping:

If an entity has a map of values for a property then this property can be mapped by using <map> element. A map is initialized with java.util.HashMap.

Example:

Student.java

import java.util.Map;
/**
 * This class represents a persistent class for Student.
 * @author javawithease
 */
public class Student {
	//data members
	private int studentId;
	private String firstName;
	private String lastName;
	private String className;
	private String rollNo;
	private int age;
	private Map subjects;
 
	//no-argument constructor
	public Student(){
 
	}
 
	//argument constructor
	public Student(String firstName, String lastName, 
			String className, String rollNo, int age){
		this.firstName = firstName;
		this.lastName = lastName;
		this.className = className;
		this.rollNo = rollNo;
		this.age = age;		
	}
 
	//getter and setter methods
	public int getStudentId() {
		return studentId;
	}
	public void setStudentId(int studentId) {
		this.studentId = studentId;
	}
	public String getFirstName() {
		return firstName;
	}
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
	public String getLastName() {
		return lastName;
	}
	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
	public String getClassName() {
		return className;
	}
	public void setClassName(String className) {
		this.className = className;
	}
	public String getRollNo() {
		return rollNo;
	}
	public void setRollNo(String rollNo) {
		this.rollNo = rollNo;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public Map getSubjects() {
		return subjects;
	}
	public void setSubjects(Map subjects) {
		this.subjects = subjects;
	}
}

Subject.java

/**
 * This class represents a persistent class for Subject.
 * @author javawithease
 */
public class Subject {
	//data members
	private int subjectId;
	private String subjectName;
 
	//no argument constructor
	public Subject(){
 
	}
 
	//argument constructor
	public Subject(String subjectName){
		this.subjectName = subjectName;
	}
 
	//getter and setter methods
	public int getSubjectId() {
		return subjectId;
	}
	public void setSubjectId(int subjectId) {
		this.subjectId = subjectId;
	}
	public String getSubjectName() {
		return subjectName;
	}
	public void setSubjectName(String subjectName) {
		this.subjectName = subjectName;
	}	
 
}

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration SYSTEM
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 
<hibernate-configuration>
 
    <session-factory>
        <property name="dialect">
           org.hibernate.dialect.OracleDialect
        </property>
        <property name="connection.url">
           jdbc:oracle:thin:@localhost:1521:XE
        </property>
        <property name="connection.username">
           system
        </property>
        <property name="connection.password">
           oracle
        </property>
        <property name="connection.driver_class">
           oracle.jdbc.driver.OracleDriver
        </property>
        <property name="hbm2ddl.auto">
           update
        </property>
        <property name="show_sql">
           true
        </property>
 
        <mapping resource="student.hbm.xml"/>
        <mapping resource="subject.hbm.xml"/>
 
    </session-factory>
 
</hibernate-configuration>

student.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping SYSTEM
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 
<hibernate-mapping>
 
 <class name="com.javawithease.business.Student" table="Student">
  <id name="studentId" type="int" column="Student_Id">
	<generator class="native"></generator>
  </id>
 
  <property name="firstName" column="First_Name" type="string"/>
  <property name="lastName" column="Last_Name" type="string"/>
  <property name="className" column="Class" type="string"/>
  <property name="rollNo" column="RollNo" type="string"/>
  <property name="age" column="Age" type="int"/>
 
  <map name="subjects" cascade="all">
    <key column="Student_Id"/>
    <index column="Student_Class"  type=”string”/>
    <one-to-many class="com.javawithease.business.Subject"/>
  </map>
 
 </class>
 
</hibernate-mapping>

subject.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping SYSTEM
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 
<hibernate-mapping>
 
  <class name="com.javawithease.business.Subject" table="Subject">
    <id name="subjectId" type="int" column="Subject_Id">
	<generator class="native"></generator>
    </id>
 
    <property name="subjectName" column="Subject_Name"
                                        type="string"></property>
 
  </class>
 
</hibernate-mapping>

HibernateUtil.java

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
 
/**
 * This is a utility class for getting the hibernate session object.
 * @author javawithease
 */
public class HibernateUtil {
    private static final SessionFactory sessionFactory = 
                                           buildSessionFactory();
 
    private static SessionFactory buildSessionFactory() {
    	SessionFactory sessionFactory = null;
        try {
        	//Create the configuration object.
        	Configuration configuration = new Configuration(); 
        	//Initialize the configuration object 
                //with the configuration file data
        	configuration.configure("hibernate.cfg.xml");
        	// Get the SessionFactory object from configuration.
        	sessionFactory = configuration.buildSessionFactory();
        }
        catch (Exception e) {
           e.printStackTrace();
        }
        return sessionFactory;
    }
 
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
 
}

HibernateTest.java

import java.util.HashMap;
import com.javawithease.persistence.StudentDBOperations;
 
/**
 * This class is used for the hibernate operations.
 * @author javawithease
 */
public class HibernateTest {
	public static void main(String args[]){
		HashMap map = new HashMap();
		map.put("MCA1",new Subject("Data Structure"));
		map.put("MCA2",new Subject("DBMS"));
		map.put("MCA3",new Subject("Java"));
 
		//Create the student object.
		Student student = new Student("Kapil", "Chawla", 
				"MCA final", "MCA/07/59", 27);		
		student.setSubjects(map);
 
		StudentDBOperations obj = new StudentDBOperations();
		//insert student object.
		obj.addStudent(student);
 
		//show all student object.
		obj.showAllStudentDetails();
 
	}
}

StudentDBOperations.java

import java.util.List;
import java.util.Map;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.javawithease.business.Student;
import com.javawithease.business.Subject;
 
/**
 * This class contains the methods to interact with database.
 * @author javawithease
 */
public class StudentDBOperations {
	/**
	 * This method is used to insert a new student record.
	 * @param student
	 * @return studentId
	 * @author javawithease
	 */
	public Integer addStudent(Student student){
	    Transaction tx = null;
	    Integer studentId = null;
	    //Get the session object.
	    Session session = 
                 HibernateUtil.getSessionFactory().openSession();
	    try{
	         tx = session.beginTransaction();
	         studentId = (Integer) session.save(student); 
	         tx.commit();
	      }catch (HibernateException e) {
	         if(tx!=null){
	        	 tx.rollback();
	         }
	         e.printStackTrace(); 
	      }finally {
	         session.close(); 
	      }
	      return studentId;	
	}
 
	/**
	 * This method is used retrieve and show the records.
	 * @author javawithease
	 */
	public void showAllStudentDetails(){
	    Transaction tx = null;
	    //Get the session object.
	    Session session = 
                   HibernateUtil.getSessionFactory().openSession();
	    try{
	         tx = session.beginTransaction();
	         List<Student> students = 
                        session.createQuery("FROM Student").list();
	         for(Student student : students){
	        	 System.out.println("First Name: "
                                         + student.getFirstName()); 
	        	 System.out.println("Last Name: " 
                                          + student.getLastName()); 
	        	 System.out.println("Class: " 
                                         + student.getClassName()); 
	        	 System.out.println("RollNo: " 
                                            + student.getRollNo()); 
	        	 System.out.println("Age: " 
                                               + student.getAge()); 
	        	 Map subject = student.getSubjects();
	        	 System.out.println("Subject Name:" + 
	        	        ((Subject)subject.get("MCA1"))
                                                .getSubjectName());
	        	 System.out.println("Subject Name:" + 
	        	         ((Subject)subject.get("MCA2"))
                                                .getSubjectName());
	        	 System.out.println("Subject Name:" + 
	        	          ((Subject)subject.get("MCA3"))
                                                .getSubjectName());
	         }
	         tx.commit();
	      }catch (HibernateException e) {
	         if(tx!=null){
	        	 tx.rollback();
	         }
	         e.printStackTrace(); 
	      }finally {
	         session.close(); 
	      }
	}
}

Output:

Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into Student (First_Name, Last_Name, Class, 
RollNo, Age, Student_Id) values (?, ?, ?, ?, ?, ?)
Hibernate: insert into Subject 
(Subject_Name, Subject_Id) values (?, ?)
Hibernate: insert into Subject 
(Subject_Name, Subject_Id) values (?, ?)
Hibernate: insert into Subject 
(Subject_Name, Subject_Id) values (?, ?)
Hibernate: update Subject set Student_Id=?, 
Subject_Class=? where Subject_Id=?
Hibernate: update Subject set Student_Id=?, 
Subject_Class=? where Subject_Id=?
Hibernate: update Subject set Student_Id=?, 
Subject_Class=? where Subject_Id=?
Hibernate: select student0_.Student_Id as Student1_0_, 
student0_.First_Name as First2_0_, student0_.Last_Name as 
Last3_0_, student0_.Class as Class0_, student0_.RollNo as 
RollNo0_, student0_.Age as Age0_ from Student student0_
First Name: Kapil
Last Name: Chawla
Class: MCA final
RollNo: MCA/07/59
Age: 27
Hibernate: select subjects0_.Student_Id as Student3_1_, 
subjects0_.Subject_Id as Subject1_1_, subjects0_.Subject_Class 
as Subject4_1_, subjects0_.Subject_Id as Subject1_1_0_, 
subjects0_.Subject_Name as Subject2_1_0_ from Subject 
subjects0_ where subjects0_.Student_Id=?
Subject Name:Data Structure
Subject Name:DBMS
Subject Name:Java

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