Hibernate One to Many Mapping Insert Query Example

One-to-Many:  according to database terminology, one row of table related with multiple rows of other table

                                                                       [or]

According to hibernate, one object of one pojo class related to multiple objects of other pojo

I mean, one [parent] to many [Children], example of one-to-many is some thing category books contains different type of books, one vendor contains lot of customers bla bla.

To achieve one-to-many between two pojo classes in the hibernate, then the following two changes are required

• In the parent pojo class, we need to take a collection property, the collection can be either Set,List,Map (We will see the example on separate collection later)
• In the mapping file of that parent pojo class, we need to configure the collection

I will take this vendor-customer as an example..

Hibernate One-To-Many Insert Query

files required…

• Vendor.java [pojo class]
• Customer.java [pojo class]
• OurLogic.java
• Customer.hbm.xml
• hibernate.cfg.xml
• Vendor.hbm.xml

Vendor.java

123456789101112131415161718192021222324252627282930package str;

import java.util.Set;

public class Vendor {

private int vendorId;
private String vendorName;

private Set children;

public int getVendorId() { return vendorId; } public void setVendorId(int vendorId) { this.vendorId = vendorId; } public String getVendorName() { return vendorName; } public void setVendorName(String vendorName) { this.vendorName = vendorName; } public Set getChildren() { return children; } public void setChildren(Set children) { this.children = children; } }

Customer.java

12345678910111213141516171819202122232425262728package str;
public class Customer {

private int customerId;
private String customerName;

private int forevenId;

public int getCustomerId() { return customerId; } public void setCustomerId(int customerId) { this.customerId = customerId; } public String getCustomerName() { return customerName; } public void setCustomerName(String customerName) { this.customerName = customerName; } public int getForevenId() { return forevenId; } public void setForevenId(int forevenId) { this.forevenId = forevenId; } }

Customer.hbm.xml

123456789101112131415<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
<class name="str.Customer" table="customer">

<id name="customerId" column="custid"  />
<property name="customerName" column="custname" length="10"/>

<property name="forevenId" column="forevenid"  insert="false" />

</class> </hibernate-mapping>

Vendor.hbm.xml

1234567891011121314151617181920<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
<class name="str.Vendor" table="vendor">

<id name="vendorId" column="vendid"  />
<property name="vendorName" column="vendname" length="10"/>

<set name="children" cascade="all" >

<key column="forevenid" />

<one-to-many class="str.Customer" />

</set>

</class> </hibernate-mapping>

See line number 12,  this time i used one new attribute cascade=”all” we will see about this attribute later as separate topic.

hibernate.cfg.xml

123456789101112131415161718192021<?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="connection.driver_class">oracle.jdbc.driver.OracleDriver
</property>
<property name="connection.url">jdbc:oracle:thin:@www.java4s.com:1521:XE</property>
<property name="connection.username">system</property>
<property name="connection.password">admin</property>

<property name="dialect">org.hibernate.dialect.OracleDialect</property>
<property name="show_sql">true</property>
<property name="hbm2ddl.auto">update</property>

<mapping resource="Customer.hbm.xml"></mapping>
<mapping resource="Vendor.hbm.xml"></mapping>
</session-factory>
</hibernate-configuration>

OurLogic.java

1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162package str;

import java.util.HashSet;
import java.util.Set;

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

public class OurLogic {

public static void main(String args[])
{

Configuration cfg = new Configuration();
cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();
Session session = factory.openSession();

//parent object

Vendor v =new Vendor(); v.setVendorId(101); v.setVendorName("java4s");

//creating 3 child objects

Customer c1=new Customer(); c1.setCustomerId(504); c1.setCustomerName("customer4"); Customer c2=new Customer(); c2.setCustomerId(505); c2.setCustomerName("customer5"); Customer c3=new Customer(); c3.setCustomerId(506); c3.setCustomerName("customer6");

// adding child objects to set, as we taken 3rd property set in parent

Set s=new HashSet(); s.add(c1); s.add(c2); s.add(c3); v.setChildren(s); Transaction tx = session.beginTransaction(); session.save(v); tx.commit(); session.close(); System.out.println("One To Many is Done..!!"); factory.close(); } }

Notes:

• In Vendor.java, we have taken a property of type Set
• In Customer.java, we have taken one property forevenId of type int to insert Vendor id

Regarding Vendor.hbm.xml

• In this mapping file, we used a collection configuration element (Set), because in pojo class of vendor, we used the collection type as Set, (we can use Map,List too)
• In order to transfer 0perations on parent object to child object we need to add cascade attribute
• By default, cascade value is none, it means even though relationship is exist, the operations we are doing on parent will not transfer to child, i mean to say here operations are insert, delete, update
• In our Vendor.hbm.xml,  we used cascade =”all” means all operations at parent object will be transfer to child
• while applying relationships, we need to configure the foreign key column name, by using which the relationship is done
• Inthe mapping file, we need to use <key /> eliment to configure foregin key column name, in this example forevenid is foreign key
• <one-to-many> is child class with which relation been done,  in our example str.Customer is the class [str is the package]