February 27th, 2023
@ManyToMany Mapping
We use ManyToMany when Multiple relations are between tables.
4.0.0
org.springframework.boot
spring-boot-starter-parent
3.0.2
com.brains.jpa.hibernate
jpa-hibernate-demo
0.0.1-SNAPSHOT
jpa-hibernate-demo
Demo project for Spring Boot
17
org.springframework.boot
spring-boot-starter-data-jpa
org.springframework.boot
spring-boot-starter-web
com.h2database
h2
runtime
org.projectlombok
lombok
true
org.springframework.boot
spring-boot-starter-test
test
org.springframework.boot
spring-boot-maven-plugin
org.projectlombok
lombok
spring.datasource.url=jdbc:h2:mem:testdb;NON_KEYWORDS=USER;DB_CLOSE_ON_EXIT=FALSE
spring.h2.console.enabled=true
spring.jpa.defer-datasource-initialization=true
# Turn Statistics ON
#spring.jpa.properties.hibernate.generate_statistics=true
logging.level.org.hibernate.stat=debug
#logging.level.root=trace
# Show all queries
spring.jpa.show-sql=true
# Format the queries
spring.jpa.properties.hibernate.format_sql=true
SELECT * FROM STUDENT_COURSE, STUDENT, COURSE
where STUDENT_COURSE.student_id = STUDENT.id
and STUDENT_COURSE.course_id = COURSE.id
One Course has many students and One Student can enroll many courses.
@Setter(value = AccessLevel.NONE)
– This removes the setter method@JoinTable(name = "STUDENT_COURSE)"
– Give a custom name to the join tablejoinColumns = @JoinColumn(name = "STUDENT_ID")
– Give a custom name to the owning columninverseJoinColumns = @JoinColumn(name = "COURSE_ID")
– Give a custom name to the referenced columnmappedBy
is always added to the non-owning side of the relationship.
package com.brains.jpa.hibernate.jpahibernatedemo.entity;
import java.util.ArrayList;
import java.util.List;
import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.FetchType;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.JoinColumn;
import jakarta.persistence.JoinTable;
import jakarta.persistence.ManyToMany;
import jakarta.persistence.OneToOne;
import lombok.AccessLevel;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.NonNull;
import lombok.RequiredArgsConstructor;
import lombok.Setter;
import lombok.ToString;
@Entity
@Data @NoArgsConstructor(access = AccessLevel.PROTECTED)
@AllArgsConstructor
@RequiredArgsConstructor
public class Student {
@Id
@GeneratedValue
private Long id;
@NonNull
@Column(nullable = false)
private String name;
@OneToOne(fetch = FetchType.LAZY)
private Passport passport;
@ToString.Exclude
@ManyToMany
@Setter(value = AccessLevel.NONE)
@JoinTable(name = "STUDENT_COURSE",
joinColumns = @JoinColumn(name = "STUDENT_ID"),
inverseJoinColumns = @JoinColumn(name = "COURSE_ID")
)
private List courses = new ArrayList<>();
public void addCourse(Course course) {
this.courses.add(course);
}
}
package com.brains.jpa.hibernate.jpahibernatedemo.entity;
import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;
import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;
import jakarta.persistence.Entity;
import jakarta.persistence.FetchType;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.ManyToMany;
import jakarta.persistence.OneToMany;
import lombok.AccessLevel;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.Setter;
@Entity
@Data
@NoArgsConstructor(access = AccessLevel.PROTECTED)
public class Course {
@Id
@GeneratedValue
private Long id;
private String name;
@Setter(AccessLevel.NONE)
@OneToMany(mappedBy = "course", fetch = FetchType.LAZY)
private List reviews = new ArrayList<>();
@ManyToMany(mappedBy = "courses")
@Setter(value = AccessLevel.NONE)
private List students = new ArrayList<>();
public void addStudent(Student student) {
this.students.add(student);
}
public void addReview(Review review) {
this.reviews.add(review);
}
public void removeReview(Review review) {
this.reviews.remove(review);
}
@UpdateTimestamp
private LocalDateTime lastUpdatedDate;
@CreationTimestamp
private LocalDateTime createdDate;
public Course(String name) {
this.name = name;
}
}
package com.brains.jpa.hibernate.jpahibernatedemo.entity;
import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.FetchType;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.OneToOne;
import lombok.AccessLevel;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.NonNull;
import lombok.RequiredArgsConstructor;
import lombok.ToString;
@Entity
@Data @NoArgsConstructor(access = AccessLevel.PROTECTED)
@AllArgsConstructor
@RequiredArgsConstructor
public class Passport {
@Id
@GeneratedValue
private Long id;
@NonNull
@Column(nullable = false)
private String number;
@ToString.Exclude
@OneToOne(fetch = FetchType.LAZY, mappedBy = "passport")
private Student student;
}
package com.brains.jpa.hibernate.jpahibernatedemo.entity;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.ManyToOne;
import lombok.AccessLevel;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.NonNull;
import lombok.RequiredArgsConstructor;
import lombok.ToString;
@Entity
@Data @NoArgsConstructor(access = AccessLevel.PROTECTED)
@AllArgsConstructor
@RequiredArgsConstructor
public class Review {
@Id
@GeneratedValue
private Long id;
@NonNull
private String rating;
@NonNull
private String description;
@ToString.Exclude
@ManyToOne
private Course course;
}
insert into course(id, name, created_date, last_updated_date)
values(10001, 'JPA in 5 steps', LOCALTIMESTAMP, LOCALTIMESTAMP);
insert into course(id, name, created_date, last_updated_date)
values(10002, 'JDBC in 10 steps', LOCALTIMESTAMP, LOCALTIMESTAMP);
insert into course(id, name, created_date, last_updated_date)
values(10003, 'JPQL in 50 steps', LOCALTIMESTAMP, LOCALTIMESTAMP);
insert into passport(id, number)
values(40001,'E12345');
insert into passport(id, number)
values(40002,'F212345');
insert into passport(id, number)
values(40003,'G12345');
insert into student(id, name, passport_id)
values(20001,'Ranga',40001);
insert into student(id, name, passport_id)
values(20002,'Adam',40002);
insert into student(id, name, passport_id)
values(20003,'Jane',40003);
insert into review(id, rating, description, course_id)
values(50001,'1', 'Great course', 10001);
insert into review(id, rating, description, course_id)
values(50002,'3', 'Nice course', 10001);
insert into review(id, rating, description, course_id)
values(50004,'5', 'Good you are writing', 10003);
insert into student_course(student_id, course_id)
values(20001, 10001);
insert into student_course(student_id, course_id)
values(20002, 10001);
insert into student_course(student_id, course_id)
values(20003, 10001);
insert into student_course(student_id, course_id)
values(20001, 10003);
package com.brains.jpa.hibernate.jpahibernatedemo.repository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;
import com.brains.jpa.hibernate.jpahibernatedemo.entity.Course;
import com.brains.jpa.hibernate.jpahibernatedemo.entity.Passport;
import com.brains.jpa.hibernate.jpahibernatedemo.entity.Student;
import jakarta.persistence.EntityManager;
import jakarta.transaction.Transactional;
@Repository
@Transactional
public class StudentRepository {
private Logger logger = LoggerFactory.getLogger(getClass());
@Autowired
EntityManager em;
public Student findById(Long id) {
return em.find(Student.class, id);
}
public void saveStudentWithPassport() {
Passport passport = new Passport("Z12345");
em.persist(passport);
Student student1 = new Student("Mike");
student1.setPassport(passport);
passport.setStudent(student1);
em.persist(student1);
}
public void someOperationToUnderstandPersistanceContext() {
Student student = em.find(Student.class, 20001L);
logger.info("Student -> {}", student);
Passport passport = student.getPassport();
logger.info("Passport -> {}", passport);
passport.setNumber("E12345-0");
student.setName("Ranga - updated");
logger.info("Student -> {}", student);
}
public void insertHardcodedStudentCourse() {
Student student = new Student("Jack");
Course course = new Course("Microservices in 100 Steps");
em.persist(student);
em.persist(course);
student.addCourse(course);
course.addStudent(student);
}
public void insertStudentCourse(Student student, Course course) {
em.persist(student);
em.persist(course);
student.addCourse(course);
course.addStudent(student);
}
}
package com.brains.jpa.hibernate.jpahibernatedemo.repository;
import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import com.brains.jpa.hibernate.jpahibernatedemo.JpaHibernateDemoApplication;
import com.brains.jpa.hibernate.jpahibernatedemo.entity.Course;
import com.brains.jpa.hibernate.jpahibernatedemo.entity.Student;
import jakarta.persistence.EntityManager;
import jakarta.transaction.Transactional;
@SpringBootTest(classes = JpaHibernateDemoApplication.class)
class StudentCourseRepositoryTest {
private Logger logger = LoggerFactory.getLogger(getClass());
@Autowired
EntityManager em;
@Test
@Transactional
void retrieveStudentAndCourse() {
Student student = em.find(Student.class, 20001L);
logger.info("Student: -> {}", student);
logger.info("Courses: -> {}", student.getCourses());
}
@Test
@Transactional
void retrieveCourseAndStudent() {
Course course = em.find(Course.class, 10001L);
logger.info("Courses: -> {}", course);
logger.info("Student: -> {}", course.getStudents());
}
}
package com.brains.jpa.hibernate.jpahibernatedemo;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import com.brains.jpa.hibernate.jpahibernatedemo.entity.Course;
import com.brains.jpa.hibernate.jpahibernatedemo.entity.Student;
import com.brains.jpa.hibernate.jpahibernatedemo.repository.StudentRepository;
@SpringBootApplication
public class JpaHibernateDemoApplication implements CommandLineRunner {
public static void main(String[] args) {
SpringApplication.run(JpaHibernateDemoApplication.class, args);
}
private Logger logger = LoggerFactory.getLogger(this.getClass());
@Autowired
private StudentRepository studentRepository;
@Override
public void run(String... args) throws Exception {
studentRepository.insertHardcodedStudentCourse();
Student student = new Student("Jack1");
Course course = new Course("Microservices in 10 Steps");
studentRepository.insertStudentCourse(student, course);
}
}
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