Hibernate Many-to-Many Mapping

Many-to-Many Hibernate Mapping with Example

In Many-to-Many association mapping, more than one objects of a persistent class are associated with more than one objects of another persistent class. For example, many (categories) are related to many (items) and vice-versa as it is a bidirectional mapping.

Here, we are creating an example of many-to-many association mapping. In this example, we need to specify @ManyToMany and @JoinTable annotations in the persistent class. Here, we need to take a collection property like Set, Map, Bag, and List in both persistent classes.

Following are the steps to create the example:

Create all Persistent classes

In this step, we are going to develop persistent classes, i.e., Categories.java and Items.java.

Categories.java


import java.util.Set;
 import javax.persistence.CascadeType;
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.Id; 
 import javax.persistence.JoinColumn;
 import javax.persistence.JoinTable;
 import javax.persistence.ManyToMany;
 import javax.persistence.Table;
 @Entity 
 @Table(name="categories")
 public class Categories {
  @Id
  @Column(name="c_id")
  private int cate_id;
  @Column(name="c_name") 
  private String cate_name;
  @ManyToMany(targetEntity=Items.class, cascade=CascadeType.ALL)
  @JoinTable(name="cate_items",joinColumns=@JoinColumn(name="c_id_fk",referencedColumnName="c_id"),inverseJoinColumns=@JoinColumn(name="item_id_fk",referencedColumnName="i_id")) 
  private Set items;
  public int getCate_id() {
  return cate_id;
  } 
  public void setCate_id(int cate_id) {
  this.cate_id = cate_id;
  }
  public String getCate_name() { 
  public void setCate_id(int cate_id) {
  this.cate_id = cate_id;
  }
  public String getCate_name() {
  return cate_name; 
  }
  public void setCate_name(String cate_name) {
  this.cate_name = cate_name;
  }
  public Set getItems() {
  return items; 
  }
  public void setItems(Set items) {
  this.items = items;
  }
  }

import java.util.Set;

import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

@Entity

@Table(name="categories")

public class Categories {

@Id

@Column(name="c_id")

private int cate_id;

@Column(name="c_name")

private String cate_name;

@ManyToMany(targetEntity=Items.class, cascade=CascadeType.ALL)

@JoinTable(name="cate_items",joinColumns=@JoinColumn(name="c_id_fk",referencedColumnName="c_id"),inverseJoinColumns=@JoinColumn(name="item_id_fk",referencedColumnName="i_id"))

private Set items;

public int getCate_id() {

return cate_id;

}

public void setCate_id(int cate_id) {

this.cate_id = cate_id;

}

public String getCate_name() {

public void setCate_id(int cate_id) {

this.cate_id = cate_id;

}

public String getCate_name() {

return cate_name;

}

public void setCate_name(String cate_name) {

this.cate_name = cate_name;

}

public Set getItems() {

return items;

}

public void setItems(Set items) {

this.items = items;

}

Items.java


import java.util.Set;
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.Id;
 import javax.persistence.ManyToMany;
 import javax.persistence.Table; 
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.Id;
 import javax.persistence.ManyToMany;
 import javax.persistence.Table; 
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.Id;
 import javax.persistence.ManyToMany;
 import javax.persistence.Table; 
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.Id;
 import javax.persistence.ManyToMany;
 import javax.persistence.Table; 
 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.Id;
 import javax.persistence.ManyToMany;
 import javax.persistence.Table;
 @Entity
 @Table(name="items")
 public class Items {
  @Id
  @Column(name="i_id")
  private int item_id;
  @Column(name="i_name")  
  private String item_name;
  @ManyToMany(targetEntity=Categories.class,mappedBy="items")
  private Set categories;
  public int getItem_id() {
  return item_id;
  } 
  public void setItem_id(int item_id) {
  this.item_id = item_id;
  }
  public String getItem_name() {
  return item_name;
  } 
  public void setItem_name(String item_name) {
  this.item_name = item_name;
  }
  public Set getCategories() {
  return categories;
  }
  public void setCategories(Set categories) { 
  this.categories = categories;
  }
  }

import java.util.Set;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

@Entity

@Table(name="items")

public class Items {

@Id

@Column(name="i_id")

private int item_id;

@Column(name="i_name")

private String item_name;

@ManyToMany(targetEntity=Categories.class,mappedBy="items")

private Set categories;

public int getItem_id() {

return item_id;

}

public void setItem_id(int item_id) {

this.item_id = item_id;

}

public String getItem_name() {

return item_name;

}

public void setItem_name(String item_name) {

this.item_name = item_name;

}

public Set getCategories() {

return categories;

}

public void setCategories(Set categories) {

this.categories = categories;

}

Create the configuration file

In this step, we are going to create the configuration class (hibernate.cfg.xml) which contains the information of persistent class and the database.

hibernate.cfg.xml


<?xml version='1.0' encoding='UTF-8'?> 
 <!DOCTYPE hibernate-configuration PUBLIC 
 "-//Hibernate/Hibernate Configuration DTD 5.3//EN" 
 "http://hibernate.sourceforge.net/hibernate-configuration-5.3.dtd"> 
 <hibernate-configuration> 
 <session-factory>  
 <property name="hibernate.hbm2ddl.auto">update</property> 
 <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
 <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
 <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property>
 <property name="connection.username">root</property>
 <property name="connection.password">root</property> 
  <mapping class="com.app.Manytomany.Categories"/>
  <mapping class="com.app.Manytomany.Items"/>
 </session-factory> 
 </hibernate-configuration>

<?xml version='1.0' encoding='UTF-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 5.3//EN"

"http://hibernate.sourceforge.net/hibernate-configuration-5.3.dtd">

<hibernate-configuration>

<session-factory>

<property name="hibernate.hbm2ddl.auto">update</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>

<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property>

</session-factory>

</hibernate-configuration>

Create the main class that stores the object of the persistent class

In this step, we are going to create a class which consists of main() method, and stores the objects of persistent classes.

App.java


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 App  
 {
  public static void main( String[] args )
  {
  Configuration cfg= new Configuration();
  cfg.configure("hibernate.cfg.xml");
  SessionFactory factory = cfg.buildSessionFactory(); 
  Session session= factory.openSession();
  Categories cate1 = new Categories();
  cate1.setCate_id(01);
  cate1.setCate_name("category 01");
  Categories cate2 = new Categories();
  cate2.setCate_id(02); 
  cate2.setCate_name("category 02");
  Items i= new Items();
  i.setItem_id(31);
  i.setItem_name("item 11");
  Items i2 =new Items();
  i2.setItem_id(32);
  i2.setItem_name("item 21"); 
  Set set= new HashSet();
  set.add(i);
  set.add(i2);
  cate1.setItems(set);
  cate2.setItems(set);
  Transaction t= session.beginTransaction(); 
  session.save(cate1);
  session.save(cate2);
  t.commit();
  System.out.println("saved successfully!!!!");
  session.close();
  }
 }

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 App

{

public static void main( String[] args )

{

Configuration cfg= new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory factory = cfg.buildSessionFactory();

Session session= factory.openSession();

Categories cate1 = new Categories();

cate1.setCate_id(01);

cate1.setCate_name("category 01");

Categories cate2 = new Categories();

cate2.setCate_id(02);

cate2.setCate_name("category 02");

Items i= new Items();

i.setItem_id(31);

i.setItem_name("item 11");

Items i2 =new Items();

i2.setItem_id(32);

i2.setItem_name("item 21");

Set set= new HashSet();

set.add(i);

set.add(i2);

cate1.setItems(set);

cate2.setItems(set);

Transaction t= session.beginTransaction();

session.save(cate1);

session.save(cate2);

t.commit();

System.out.println("saved successfully!!!!");

session.close();

}

Output

Database tables

categories table

items table

cate_items table

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