Hibernate many to many mapping example

This is 5 of 8 parts of tutorial series

Tutorial Content:

• Introduction to hibernate framework
• Hibernate hello world example in eclipse
• Difference between openSession and getCurrentSession
• Hibernate one to one mapping example
• Hibernate one to many mapping example
• Hibernate many to many mapping example
• Hibernate inheritance:Table per class hierarchy
• Hibernate inheritance:table per subclass
• Hibernate inheritance:Table per concrete class
• Difference between openSession and getCurrentSession
• Difference between get and load
• Spring MVC Hibernate MySQL CRUD example
• Spring Rest hibernate example

In this example we will see how to implement many to many relationship using annotations.
Lets take example of Country and Language.One Country can have n number of languages and one language can be spoken by n number of countries.Following is relationship diagram among them.

Now to create above tables in database, you need to create two java files i.e. Country.java and Language.java.

1.Country.java

Country class will be used to create COUNTRY table in database.
Create Country.java in src->org.arpit.javapostsforlearning.

package org.arpit.javapostsforlearning;
import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name="COUNTRY")
public class Country {

 @Id
 @GeneratedValue
 @Column(name="Country_Id")
 int countryId;

 @Column(name="Country_Name")
    String countryName ;

 @ManyToMany(cascade=CascadeType.ALL)
 @JoinTable(name="COUNTRY_LANGUAGE",joinColumns={@JoinColumn(name="Country_Id")},inverseJoinColumns={@JoinColumn(name="Language_Id")})
 Collection languages=new ArrayList();

 public Country()
 {

 }
    public Country(String countryName) {
  this.countryName=countryName;
 }

 public String getCountryName() {
        return countryName;
    }

    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }

 public Collection getLanguages() {
  return languages;
 }

 public void setLanguages(ArrayList languages) {
  this.languages = languages;
 }
}

The @MamyToMany annotation is used to create the many-to-many relationship between the Country and Language entities. The @JoinTable annotation is used to create the COUNTRY_LANGUAGE link table and @JoinColumn annotation is used to refer the linking columns in both the tables.

2.Langauge.java

Language class will be used to create LANGUAGE table in database.
Create Langauge.java in src->org.arpit.javapostsforlearning.

package org.arpit.javapostsforlearning;import javax.persistence.Column;
import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name="LANGUAGE")
public class Language {

 @Id
 @GeneratedValue
 @Column(name="Language_Id")
 int languageId;

 @Column(name="Language_Name")
 String languageName;

 @ManyToMany(mappedBy="languages")
 Collection languageSpeakingCountries=new ArrayList();

 public Language()
 {

 }
 public Language(String languageName) {
  this.languageName=languageName;
 }

 public String getLanguageName() {
  return languageName;
 }

 public void setLanguageName(String languageName) {
  this.languageName = languageName;
 }

 public Collection getLanguageSpeakingCountries() {
  return languageSpeakingCountries;
 }

 public void setLanguageSpeakingCountries(ArrayList languageSpeakingCountries) {
  this.languageSpeakingCountries = languageSpeakingCountries;
 }
}