Spring Boot and Hibernate Many-to-Many CRUD REST API Tutorial

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In this tutorial, we will demonstrate how to set up a many-to-many relationship between Student and Course entities using Spring Boot and Hibernate, and expose CRUD operations through a REST API.

Prerequisites

1. Java Development Kit (JDK) 11 or higher: Ensure JDK is installed and configured on your system.
2. Integrated Development Environment (IDE): IntelliJ IDEA, Eclipse, or any other IDE.
3. Maven: Ensure Maven is installed and configured on your system.

Step 1: Create a Spring Boot Project

1. Open your IDE and create a new Spring Boot project.
2. Use Spring Initializr or manually create the pom.xml file to include Spring Boot and other required dependencies.

<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.example</groupId> <artifactId>spring-boot-many-to-many-example</artifactId> <version>1.0-SNAPSHOT</version> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>3.1.0</version> <relativePath/> </parent> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>com.h2database</groupId> <artifactId>h2</artifactId> <scope>runtime</scope> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project> 

Explanation

• spring-boot-starter-data-jpa: Includes Spring Data JPA with Hibernate.
• spring-boot-starter-web: Includes Spring MVC for building web applications.
• h2: An in-memory database for testing purposes.

Step 2: Configure the Application Properties

Configure the application.properties file to set up the H2 database.

spring.datasource.url=jdbc:h2:mem:testdb spring.datasource.driverClassName=org.h2.Driver spring.datasource.username=sa spring.datasource.password= spring.jpa.database-platform=org.hibernate.dialect.H2Dialect spring.h2.console.enabled=true spring.jpa.hibernate.ddl-auto=update spring.jpa.show-sql=true spring.jpa.properties.hibernate.format_sql=true 

Step 3: Create the Student Entity Class

Create a package named com.example.entity and a class named Student.

package com.example.entity; import jakarta.persistence.*; import java.util.HashSet; import java.util.Set; @Entity public class Student { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String name; @ManyToMany(cascade = CascadeType.ALL) @JoinTable( name = "student_course", joinColumns = @JoinColumn(name = "student_id"), inverseJoinColumns = @JoinColumn(name = "course_id") ) private Set<Course> courses = new HashSet<>(); public Student() {} public Student(String name) { this.name = name; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Set<Course> getCourses() { return courses; } public void setCourses(Set<Course> courses) { this.courses = courses; } public void addCourse(Course course) { courses.add(course); course.getStudents().add(this); } public void removeCourse(Course course) { courses.remove(course); course.getStudents().remove(this); } @Override public String toString() { return "Student{id=" + id + ", name='" + name + '\'' + '}'; } } 

Explanation

• @Entity: Marks the class as an entity.
• @Id: Marks the field as the primary key.
• @GeneratedValue: Specifies the strategy for generating values for the primary key.
• @ManyToMany: Defines a many-to-many relationship with the Course entity.
• @JoinTable: Specifies the join table.
• @JoinColumn: Specifies the foreign key column for the current entity.
• @inverseJoinColumns: Specifies the foreign key column for the other entity in the relationship.

Step 4: Create the Course Entity Class

Create a class named Course in the same package.

package com.example.entity; import jakarta.persistence.*; import java.util.HashSet; import java.util.Set; @Entity public class Course { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String name; @ManyToMany(mappedBy = "courses") private Set<Student> students = new HashSet<>(); public Course() {} public Course(String name) { this.name = name; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } @Override public String toString() { return "Course{id=" + id + ", name='" + name + '\'' + '}'; } } 

Explanation

• @Entity: Marks the class as an entity.
• @Id: Marks the field as the primary key.
• @GeneratedValue: Specifies the strategy for generating values for the primary key.
• @ManyToMany: Defines a many-to-many relationship with the Student entity.
• mappedBy: Specifies the field in the Student entity that owns the relationship.

Step 5: Create Repository Interfaces

Create a package named com.example.repository and interfaces for Student and Course.

package com.example.repository; import com.example.entity.Student; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.stereotype.Repository; @Repository public interface StudentRepository extends JpaRepository<Student, Long> {} 

package com.example.repository; import com.example.entity.Course; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.stereotype.Repository; @Repository public interface CourseRepository extends JpaRepository<Course, Long> {} 

Step 6: Create Service Classes

Create a package named com.example.service and service classes for Student and Course.

package com.example.service; import com.example.entity.Student; import com.example.entity.Course; import com.example.repository.StudentRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import java.util.List; @Service public class StudentService { @Autowired private StudentRepository studentRepository; public Student save(Student student) { return studentRepository.save(student); } public List<Student> findAll() { return studentRepository.findAll(); } public Student findById(Long id) { return studentRepository.findById(id).orElse(null); } public void deleteById(Long id) { studentRepository.deleteById(id); } public Student addCourse(Long studentId, Course course) { Student student = findById(studentId); if (student != null) { student.addCourse(course); return save(student); } return null; } public Student removeCourse(Long studentId, Long courseId) { Student student = findById(studentId); if (student != null) { Course course = student.getCourses().stream().filter(c -> c.getId().equals(courseId)).findFirst().orElse(null); if (course != null) { student.removeCourse(course); return save(student); } } return null; } } 

package com.example.service; import com.example.entity.Course; import com.example.repository.CourseRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import java.util.List; @Service public class CourseService { @Autowired private CourseRepository courseRepository; public Course save(Course course) { return courseRepository.save(course); } public List<Course> findAll() { return courseRepository.findAll(); } public Course findById(Long id) { return courseRepository.findById(id).orElse(null); } public void deleteBy Id(Long id) { courseRepository.deleteById(id); } } 

Step 7: Create Controller Classes

Create a package named com.example.controller and controller classes for Student and Course.

package com.example.controller; import com.example.entity.Student; import com.example.entity.Course; import com.example.service.StudentService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.*; import java.util.List; @RestController @RequestMapping("/students") public class StudentController { @Autowired private StudentService studentService; @PostMapping public Student createStudent(@RequestBody Student student) { return studentService.save(student); } @GetMapping public List<Student> getAllStudents() { return studentService.findAll(); } @GetMapping("/{id}") public Student getStudentById(@PathVariable Long id) { return studentService.findById(id); } @DeleteMapping("/{id}") public void deleteStudent(@PathVariable Long id) { studentService.deleteById(id); } @PostMapping("/{studentId}/courses") public Student addCourse(@PathVariable Long studentId, @RequestBody Course course) { return studentService.addCourse(studentId, course); } @DeleteMapping("/{studentId}/courses/{courseId}") public Student removeCourse(@PathVariable Long studentId, @PathVariable Long courseId) { return studentService.removeCourse(studentId, courseId); } } 

package com.example.controller; import com.example.entity.Course; import com.example.service.CourseService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.*; import java.util.List; @RestController @RequestMapping("/courses") public class CourseController { @Autowired private CourseService courseService; @PostMapping public Course createCourse(@RequestBody Course course) { return courseService.save(course); } @GetMapping public List<Course> getAllCourses() { return courseService.findAll(); } @GetMapping("/{id}") public Course getCourseById(@PathVariable Long id) { return courseService.findById(id); } @DeleteMapping("/{id}") public void deleteCourse(@PathVariable Long id) { courseService.deleteById(id); } } 

Step 8: Create Main Application Class

Create a package named com.example and a class named SpringBootManyToManyExampleApplication.

package com.example; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class SpringBootManyToManyExampleApplication { public static void main(String[] args) { SpringApplication.run(SpringBootManyToManyExampleApplication.class, args); } } 

Step 9: Run the Application

1. Run the SpringBootManyToManyExampleApplication class.
2. Use an API client (e.g., Postman) or a web browser to test the endpoints.

Testing the Endpoints

1. Create a Student:

   • URL: POST /students
   • Body:

     { "name": "John Doe" } 

2. Create a Course:

   • URL: POST /courses
   • Body:

     { "name": "Math 101" } 

3. Add Course to Student:

   • URL: POST /students/{studentId}/courses
   • Body:

     { "name": "Math 101" } 

4. Get All Students:

   • URL: GET /students

5. Get Student by ID:

   • URL: GET /students/{id}

6. Delete Student by ID:

   • URL: DELETE /students/{id}

7. Get All Courses:

   • URL: GET /courses

8. Get Course by ID:

   • URL: GET /courses/{id}

9. Delete Course by ID:

   • URL: DELETE /courses/{id}

Conclusion

You have successfully created an example using Spring Boot and Hibernate to demonstrate a many-to-many relationship between Student and Course entities. This tutorial covered setting up a Spring Boot project, configuring Hibernate, creating entity classes with a many-to-many relationship, and performing CRUD operations through RESTful endpoints.