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:

1. 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;
  }
  } 

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;
  }
  } 

• 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

 
  
  
   
 update 
 org.hibernate.dialect.MySQL5Dialect
 com.mysql.jdbc.Driver
 jdbc:mysql://localhost:3306/test
 root
 root 
  
  
  
   

• 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();
  }
 } 

• Output

• Database tables

categories table

items table

cate_items table