You can map many to many relation either using set, map, bag etc. We are giving you an example of using map for many-to-many mapping. In such case, three tables will be created.
1. Question.java:
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package in.anyforum;
import java.util.Map;
public class Question {
private int id;
private String name;
private Map<String,User> answers;
public Question() {}
public Question(String name, Map<String, User> answers) {
super();
this.name = name;
this.answers = answers;
}
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 Map<String, User> getAnswers() {
return answers;
}
public void setAnswers(Map<String, User> answers) {
this.answers = answers;
}
}
2. User.java:
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package in.anyforum;
public class User {
private int id;
private String username,email,country;
public User() {}
public User(String username, String email, String country) {
super();
this.username = username;
this.email = email;
this.country = country;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
}
3. question.hbm.xml:
-----------------------------------------------
<?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>
<class name="in.anyforum.Question" table="question786">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name"></property>
<map name="answers" table="answer786" cascade="all">
<key column="questionid"></key>
<index column="answer" type="string"></index>
<many-to-many class="in.anyforum.User" column="userid"></many-to-many>
</map>
</class>
</hibernate-mapping>
4. user.hbm.xml:
------------------------------------
<?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>
<class name="in.anyforum.User" table="user786">
<id name="id">
<generator class="native"></generator>
</id>
<property name="username"></property>
<property name="email"></property>
<property name="country"></property>
</class>
</hibernate-mapping>
5. hibernate.cfg.xml:
------------------------------------------
<?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">
<!-- Generated by MyEclipse Hibernate Tools. -->
<hibernate-configuration>
<session-factory>
<property name="hbm2ddl.auto">update</property>
<property name="dialect">org.hibernate.dialect.Oracle9Dialect</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>
<mapping resource="question.hbm.xml"/>
<mapping resource="user.hbm.xml"/>
</session-factory>
</hibernate-configuration>
6. StoreTest.java:
---------------------------------------
package in.anyforum;
import java.util.HashMap;
import org.hibernate.*;
import org.hibernate.cfg.*;
public class StoreTest {
public static void main(String[] args) {
Session session=new Configuration().configure().buildSessionFactory().openSession();
Transaction tx=session.beginTransaction();
HashMap<String,User> map1=new HashMap<String,User>();
map1.put("java is a Object Oriented programming language",
new User("John Milton","john@gmail.com","usa"));
map1.put("java is a platform",
new User("Ashok Kumar","ashok@gmail.com","india"));
HashMap<String,User> map2=new HashMap<String,User>();
map2.put("servlet technology is a server side programming",
new User("John Milton","john@gmail.com","usa"));
map2.put("Servlet is an Interface",
new User("Ashok Kumar","ashok@gmail.com","india"));
Question question1=new Question("What is java?",map1);
Question question2=new Question("What is jsp?",map2);
session.persist(question1);
session.persist(question2);
tx.commit();
session.close();
System.out.println("successfully stored");
}
}
7. FetchTest.java:
----------------------------------------
package in.anyforum;
import java.util.*;
import org.hibernate.*;
import org.hibernate.cfg.*;
public class FetchTest {
public static void main(String[] args) {
Session session=new Configuration().configure().buildSessionFactory().openSession();
Query query=session.createQuery("from Question ");
List<Question> list=query.list();
Iterator<Question> iterator=list.iterator();
while(iterator.hasNext()){
Question question=iterator.next();
System.out.println("question id:"+question.getId());
System.out.println("question name:"+question.getName());
System.out.println("answers.....");
Map<String,User> map=question.getAnswers();
Set<Map.Entry<String,User>> set=map.entrySet();
Iterator<Map.Entry<String,User>> iteratoranswer=set.iterator();
while(iteratoranswer.hasNext()){
Map.Entry<String,User> entry=(Map.Entry<String,User>)iteratoranswer.next();
System.out.println("answer name:"+entry.getKey());
System.out.println("answer posted by.........");
User user=entry.getValue();
System.out.println("username:"+user.getUsername());
System.out.println("user emailid:"+user.getEmail());
System.out.println("user country:"+user.getCountry());
}
}
session.close();
}
}
