how hibernate maintain referential integrity

[IshwarJava Chand]

I have the following scenario:

Many employees can share the same address.

For which i have the following POJO classes:

1. Employee class that has properties name, designation of String type and address of Address type.
2. Address class that has properties homeNum, sector and block of String type.

The below is the Employee and Address POJO class:

  
package com.nbsl.persistence;

import java.io.Serializable;

public class Employee implements Serializable{
	
	private static final long serialVersionUID = 1L;
	private int id;
	private String name;
	private String designation;
	private Address address;
	
	public Employee(){		
	}
	
	public Employee(String name, String designation, Address address){
		this.name = name;
		this.designation = designation;
		this.address = address;
	}
	
	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getDesignation() {
		return designation;
	}

	public void setDesignation(String designation) {
		this.designation = designation;
	}

	public Address getAddress() {
		return address;
	}

	public void setAddress(Address address) {
		this.address = address;
	}
}

 

  
package com.nbsl.persistence;

import java.io.Serializable;

public class Address implements Serializable{
	
	private static final long serialVersionUID = 1L;
	private String homeNum;
	private int id;
	private String block;
	private String sector;
	
	public Address(){		
	}
	
	public Address(String homeNum, String block, String sector){
		this.homeNum = homeNum;
		this.sector = sector;
		this.block = block;
	}
	
	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getHomeNum() {
		return homeNum;
	}

	public void setHomeNum(String homeNum) {
		this.homeNum = homeNum;
	}

	public String getBlock() {
		return block;
	}

	public void setBlock(String block) {
		this.block = block;
	}

	public String getSector() {
		return sector;
	}

	public void setSector(String sector) {
		this.sector = sector;
	}	
		
	@Override
	public String toString() {
		StringBuffer strbuf = new StringBuffer();
		strbuf.append(block).append(" - ").append(homeNum).append(", ");
		strbuf.append("Sector - ").append(sector);
		return strbuf.toString();
	}
}

The below is the employee.hbm.xml file:

   
<?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 package="com.nbsl.persistence">

	<class name="Employees" table="employees">
		<id name="id" column="ID" type="integer">
			<generator class="native"/>
		</id>
		<property name="name" column="NAME" type="string"/>
		<property name="designation" column="DESIGNATION" type="string"/>
		<many-to-one name="address" column="ADDRESS_ID" class="Address" cascade="save-update,delete"/>
	</class>
	
	<class name="com.nbsl.persistence.Address" table="address">
		<id name="id" column="ADDRESS_ID" type="integer">
			<generator class="native"/>
		</id>
		<property name="homeNum" column="HOME_NUM" type="string"/>
		<property name="block" column="BLOCK" type="string"/>
		<property name="sector" column="SECTOR" type="string"/>
	</class>

</hibernate-mapping>

Some part of application code:

  
Address address = new Address("305", "C", "22");
session.save(address);
Employee ishwar = new Employee("Ishwar", "Developer", address);
Employee abhijeet = new Employee("Abhijeet", "Developer", address);
session.save(ishwar);
session.save(abhijeet);
session.flush();
Employee employee = (Employee)session.load(Employees.class, ishwar.getId());
session.delete(employee)

From the above code ishwar and abhijeet both share the same address. In this case there are 2 rows get added in the Employee table
and 1 row added in the Address table.

My question is that when I delete a employee using session.delete(employee) from the appliaction code. then from the Employee table a record for that employee get deleted and also its address entries from the Address table too get deleted. while another employee still has a reference of that address in the Employee table.

How can i prevent the address record not to get deleted from the Address table , if some employees have references of it in Employee table, when an employee is deleted.

[Paul Sturrock]

You have defined your employee - address association to use a cascade delete. If addresses are not child objects of employees you probably don't want to define them this way.

[IshwarJava Chand]

Hi Paul,

Thanks for the reply.
Can you suggest me then what is the best way to define it.

[Tejas Aj]

hi,
can you try putting a relationship(pk - fk) between the employee and address table and then try.

Regards,
Tejas.