❮❮ PREV NEXT ❯❯

Hibernate - Map Mapping

The 'Map' mapping is also same as 'List' and 'Set' mapping with minor changes. As we know a 'Map' contains a key and a value. So, we will be making changes in our code accordingly.

class Employee{
int id;
String name;
Map<String,Address> addressMap = new HashMap<String,Address> ();
---Getters & Setters---
}

We have used 'Map' to hold multiple 'Address'.

Let us follow the below steps:

1. Firstly in the mapping file we need to tell Hibernate that the 'Address' class has to be treated as a 'Map'.

<?xml version = "1.0" encoding = "utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
<class name = "Employee" table = "EMPLOYEE">

<id name = "id" type = "int">
<column name = "ID">
</id>
<property name = "name" type = "string">
<column name = "NAME">
</property>

<map name="addressSet" table="ADDRESS">
<key column="EMP_ID"/>
<map-key type="string" column="MAP_COUNTER"/>
<composite-element class="Address">
<property name = "streetName" type = "string">
<column name = "STREET_NAME">
</property>

<property name = "city" type = "string">
<column name = "CITY">
</property>

<property name = "pinCode" type = "string">
<column name = "PIN_CODE">
</property>
</composite-element>
</map>

</class>
</hibernate-mapping>

In the above statement we have informed Hibernate that multiple 'Address' has to be added to the 'ADDRESS' table and we have used 'Map' of java to achieve that.

Now, to create a link between the 'EMPLOYEE' and 'ADDRESS' table we have used the primary key 'ID' in the 'ADDRESS' table to establish a primary key - foreign key relationship.

The next line is specific to 'Map'. Since, a 'Map' manages its data in key and value pair, we need an extra column in database to store the key of the Map as well. So, we have used the <map-key> tag to create a column 'MAP_COUNTER' which will be keeping a track of the map keys in the Database side.

<map-key type="string" column="MAP_COUNTER"/>

Then we have informed Hibernate about the 'Address' class using the '<composite-element>' tag of Hibernate.

<composite-element class="Address">
<property name = "streetName" type = "string">
<column name = "STREET_NAME">
</property>
...
...
</composite-element>

2. Next, we will be writing the main class where we will be saving the 'Employee' data and its corresponding 'Address' data to the database using Hibernate.

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

public class HibernateSave {
public static void main(String[] args) {

static SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
session.beginTransaction();

Map<String,Address> addressMap = new HashMap<Address> ();

Address localAddress = new Address();
localAddress.setStreetName("Walls Street");
localAddress.setCity("Delhi");
localAddress.setPinCode("110012");

addressMap.put("Local Address",localAddress);

Address permanentAddress = new Address();
permanentAddress.setStreetName("Murugeshpalya");
permanentAddress.setCity("Bangalore");
permanentAddress.setPinCode("560019");

addressMap.put("Permanent Address",permanentAddress);

Employee employee = new Employee();
employee.setId(1);
employee.setName("Joe");
employee.setAddressMap(addressMap);
session.save(employee);

session.getTransaction().commit();

session.close();
sessionFactory().close();
}
}

So, in the above example we have created two 'Address'.

First is the local address of the Employee.

Address localAddress = new Address();
localAddress.setStreetName("Walls Street");
localAddress.setCity("Delhi");
localAddress.setPinCode("110012");

Second is the Permanent Address of the Employee.

Address permanentAddress = new Address();
permanentAddress.setStreetName("Murugeshpalya");
permanentAddress.setCity("Bangalore");
permanentAddress.setPinCode("560019");

And since the Addresses are stored in 'Map'. We have created a 'Map' type object

Map<String,Address> addressMap = new HashMap<Address> ();

to store the 'localAddress' where we have made "Local Address" as the key

addressMap.put("Local Address",localAddress);

and 'permanentAddress' where we have made "Permanent Address" as the key.

addressMap.put("Permanent Address",permanentAddress);

And finally we need to add the Map 'addressMap' to the 'Employee' object.

employee.setAddressMap(addressMap);

EMPLOYEE

ID	NAME
1	Joe

ADDRESS

MAP_COUNTER	ID	STREET_NAME	CITY	PIN_CODE
Local Address	1	Walls street	Delhi	110012
Permanent Address	1	Murugeshpalya	Bangalore	560019

If you see the above table, a new column 'MAP_COUNTER' is created in the 'ADDRESS' table which keeps track of the map key.

❮❮ PREV NEXT ❯❯