Spring Boot中两个实体之间的多对多关系

Spring Boot是一个用于创建独立的、基于Spring的应用程序的框架，它简化了开发过程并提供了一种快速、便捷的方式来构建Java应用程序。在Spring Boot中，我们可以使用JPA（Java Persistence API）来处理数据库操作。本文将介绍如何在Spring Boot中建立两个实体之间的多对多关系，并提供一个案例代码来演示。

java
@Entity
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "student_course",
            joinColumns = @JoinColumn(name = "student_id"),
            inverseJoinColumns = @JoinColumn(name = "course_id"))
    private Set courses;
    
    // 省略构造方法、getter和setter
}
@Entity
public class Course {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @ManyToMany(mappedBy = "courses", fetch = FetchType.LAZY)
    private Set students;
    
    // 省略构造方法、getter和setter
}

java
@Repository
public interface StudentRepository extends JpaRepository {
}
@Repository
public interface CourseRepository extends JpaRepository {
}

java
@Service
public class StudentService {
    @Autowired
    private StudentRepository studentRepository;
    
    @Autowired
    private CourseRepository courseRepository;
    public void addCourseToStudent(Long studentId, Long courseId) {
        Student student = studentRepository.findById(studentId).orElseThrow(() -> new RuntimeException("Student not found"));
        Course course = courseRepository.findById(courseId).orElseThrow(() -> new RuntimeException("Course not found"));
        student.getCourses().add(course);
        course.getStudents().add(student);
        studentRepository.save(student);
        courseRepository.save(course);
    }
    
    // 省略其他业务逻辑方法
}
@Service
public class CourseService {
    @Autowired
    private CourseRepository courseRepository;
    
    @Autowired
    private StudentRepository studentRepository;
    public void addStudentToCourse(Long courseId, Long studentId) {
        Course course = courseRepository.findById(courseId).orElseThrow(() -> new RuntimeException("Course not found"));
        Student student = studentRepository.findById(studentId).orElseThrow(() -> new RuntimeException("Student not found"));
        course.getStudents().add(student);
        student.getCourses().add(course);
        courseRepository.save(course);
        studentRepository.save(student);
    }
    
    // 省略其他业务逻辑方法
}

java
@RestController
public class DemoController {
    @Autowired
    private StudentService studentService;
    
    @Autowired
    private CourseService courseService;
    @PostMapping("/addCourseToStudent")
    public String addCourseToStudent(@RequestParam Long studentId, @RequestParam Long courseId) {
        studentService.addCourseToStudent(studentId, courseId);
        return "Course added to student successfully";
    }
    @PostMapping("/addStudentToCourse")
    public String addStudentToCourse(@RequestParam Long courseId, @RequestParam Long studentId) {
        courseService.addStudentToCourse(courseId, studentId);
        return "Student added to course successfully";
    }
}