many to many mapping in hibernate

 many to many mapping in hibernate

Directory Structure

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<modelVersion>4.0.0</modelVersion>

<groupId>com.test</groupId>

<artifactId>Test</artifactId>

<version>0.0.1-SNAPSHOT</version>

<packaging>jar</packaging>

<name>Test</name>

<url>http://maven.apache.org</url>

<properties>

<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

<maven.compiler.source>1.9</maven.compiler.source>

<maven.compiler.target>1.9</maven.compiler.target>

</properties>

<dependencies>

<dependency>

<groupId>junit</groupId>

<artifactId>junit</artifactId>

<version>3.8.1</version>

<scope>test</scope>

</dependency>

<dependency>

<groupId>org.hibernate</groupId>

<artifactId>hibernate-core</artifactId>

<version>5.6.8.Final</version>

</dependency>

<!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->

<dependency>

<groupId>org.projectlombok</groupId>

<artifactId>lombok</artifactId>

<version>1.18.20</version>

<scope>provided</scope>

</dependency>

<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->

<dependency>

<groupId>mysql</groupId>

<artifactId>mysql-connector-java</artifactId>

<version>8.0.22</version>

</dependency>

</dependencies>

</project>

Course

package com.test.entity;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.Table;

import lombok.AllArgsConstructor;

import lombok.Data;

import lombok.NoArgsConstructor;

@Data

@AllArgsConstructor

@NoArgsConstructor

@Entity

@Table(name = "crtab")

public class Course {

@Id

private int crId;

private String crName;

private Double crCost;

}

Student

package com.test.entity;

import java.util.HashSet;

import java.util.Set;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

import lombok.AllArgsConstructor;

import lombok.Data;

import lombok.NoArgsConstructor;

@Data

@AllArgsConstructor

@NoArgsConstructor

@Entity

@Table(name = "stdtab")

public class Student {

@Id

private int stdId;

private String stdName;

private Double stdMarks;

@ManyToMany

@JoinTable(name = "stdcrstab",

joinColumns = @JoinColumn(name="sidFk"),

inverseJoinColumns = @JoinColumn(name="cidFk")

)

private Set<Course> cobs = new HashSet<>();

}

HibernateUtil

package com.test.util;

import java.util.Properties;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import org.hibernate.cfg.Environment;

import com.test.entity.Course;

import com.test.entity.Student;

public class HibernateUtil {

static SessionFactory factory = null;

static {

Configuration cfg = new Configuration();

Properties prop = new Properties();

prop.put(Environment.URL, "jdbc:mysql://localhost:3306/new");

prop.put(Environment.USER, "root");

prop.put(Environment.PASS, "root");

prop.put(Environment.SHOW_SQL,true);

prop.put(Environment.FORMAT_SQL, true);

prop.put(Environment.HBM2DDL_AUTO, "update");

cfg.setProperties(prop);

cfg.addAnnotatedClass(Student.class);

cfg.addAnnotatedClass(Course.class);

factory = cfg.buildSessionFactory();

}

public static SessionFactory getSessionFactory() {

return factory;

}

public static Session getSession() {

return factory.openSession();

}

}

Test

package com.test;

import java.util.Set;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import com.test.entity.Course;

import com.test.entity.Student;

import com.test.util.HibernateUtil;

public class Test {

public static void main(String[] args) {

SessionFactory factory = HibernateUtil.getSessionFactory();

//get session

Session ses = HibernateUtil.getSession();

try(factory;ses){

ses.beginTransaction();

Course c1 = new Course(1,"Math",5000.0);

Course c2 = new Course(2,"Science",4000.0);

Course c3 = new Course(3,"History",6000.0);

Student s1 = new Student(101,"Ajay",97.2,Set.of(c1,c2));

Student s2 = new Student(102,"Vijay",98.2,Set.of(c2,c3));

//save

ses.save(c1);

ses.save(c2);

ses.save(c3);

ses.save(s1);

ses.save(s2);

//commit the tx

ses.getTransaction().commit();

}catch(Exception e) {

e.printStackTrace();

}

}

}