Prevent Duplicate entry in many to many relationship using JPA

Question

I have 3 tables

1. Student
2. Course
3. Enrolled Course (Join Table)

There is a many-to-many relationship between student and course. Since a student can enroll in many courses and a course can have many students enrolled.

I added the corresponding List(students) and Set(courses) in Course and Student entity classes respectively.

The Student Entity:

    @Entity
    @Table(name="Student_Tbl")
    public class Student {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id")
        private Long id;
    
        private String name;
    
        private String department;
    
        @JoinTable(
                name = "enrolled_course",
                joinColumns = @JoinColumn(name = "student_id",referencedColumnName = "id"),
                inverseJoinColumns = @JoinColumn(name = "course_id",referencedColumnName = "title"))
        @ManyToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)
        private Set<Course> courses;

The Course Entity:

    @Entity
    @Table(name="Course_Tbl")
    public class Course {
        @Id
        private String title;
    
        private String description;
    
        @ManyToMany(mappedBy = "courses",fetch = FetchType.EAGER)
        private Set<Student> students;

The Controller Class:

    @RestController
    @RequestMapping("/v1")
    public class StudentController {
      
        @Autowired
        private StudentRepository studentRepository;

        @Autowired
        private CourseRepository courseRepository;
    
        @Autowired
        private StudentService studentService;
    
        @PostMapping("/student/register")
        public ResponseEntity<Student> saveStudent(@RequestBody Student student)
        {
            studentService.saveStudent(student);
            return ResponseEntity.ok(student);
        }
    }

When I save a Student with a course, it all works well. The data is stored in all the three tables

    {
        "name":"ABC",
        "department":"CS",
        "course":[
            {
                "title":"DBMS",
                "description":"Database Management System"
            }
            
        ]
    }

But when I post another request with the same course for different students, Duplicate entry 'DBMS' for key 'course_tbl.PRIMARY' error is thrown.

How do I avoid this?

Edit:

public void saveStudent(Student student){
        for(Course course : student.getCourse() ){
            if(courseRepository.findByTitle(course.getTitle())!= null) continue;
            courseRepository.save(course);
        }
        studentRepository.save(student);
    }

Here I manually handled the case by checking if the course is already present in the table which worked as expected.