CODEWITHSUNDEEP
javamysqljpa
oneoe
oneoe

Reputation: 53

JPA and MySQL mapping entites

@Entity
@Table(name = "COURSE")
public class Course {

    @Id
    @GeneratedValue
    private Long id;

    @Column(name = "course_name")
    private String courseName;

    @ManyToOne
    Department department;

    @ManyToOne
    Student student;

    protected Course() {}

    public Course(String name, Department department) {
        this.department = department;
        courseName = name;
    }

}



@Entity
@Table(name = "STUDENT")
public class Student {
    @Id
    @GeneratedValue
    private Long id;

    @Column(name = "locker_id")
    private int lockerId;

    @OneToMany(fetch = FetchType.EAGER, mappedBy = "student",
            cascade = CascadeType.ALL)
    List<Course> courses = new ArrayList<>();

    @Embedded
    private Person attendee;

    protected Student(){}

    public Student(Person person, int lockerId) {
        attendee = person;
        this.lockerId = lockerId;
        courses = new ArrayList<>();
    }

    public void setCourse(Course course) {
        courses.add(course);
    }

    public void setCourses(List<Course> courses) {
        this.courses = courses;
    }

    public List<Course> getCourses() {
        return courses;
    }

}



@SpringBootApplication
public class UniversityApplication implements CommandLineRunner {

    @Autowired
    CourseRepository courseRepository;
    @Autowired
    DepartmentRepository departmentRepository;
    @Autowired
    StudentRepository studentRepository;

    public static void main(String[] args) {
        SpringApplication.run(UniversityApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {

        //Students
        Student one = studentRepository.save(new Student(new Person("jane", "doe"), 20));

        //Courses
        Course english101 = courseRepository.save(new Course("English 101", humanities));
        Course english202 = courseRepository.save(new Course("English 202", humanities));

        //This does not add student to a course, why?
        //Ask
        one.setCourse(english101);
        studentRepository.save(one);
        //How to map course with student and then to find students in a particular course

    }
}

I have already successfully mapped Department and Course, in course you can find the department id. I want the same thing to work for Student class, so that I can find Students id in MySQL table @ Course.

I want to add student to a specific course and save it and that does not seem to work either.

Upvotes: 0

Views: 63

Answers (3)

oneoe
oneoe

Reputation: 53

   public void setCourse(Course course) {
        courses.add(course);
        course.setStudent(this);
    }

I just had to set the Student for this course in this method to make the mapping work.

Upvotes: 0

Kai
Kai

Reputation: 71

The problem is that your @ManyToOne relationship doesn't know how to connect the tables. Please change:

 @ManyToOne
Student student;

to:

@ManyToOne
@JoinColumn(name = "student_id")
Student student;

here is a good explanation about @JoinColumns and "mappedBy"

Upvotes: 1

Alex
Alex

Reputation: 98

Try to enable query generation log, to check what queries exactly are generated. If you will not see any INSERT/UPDATE queries I would assume problems with transactions. Need to make you call transactional.

Upvotes: 0

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