Hibernate Many-To-Many Mapping Using Annotations Part -1

 In this example you will learn how to map many-to-many relationship using Hibernate Annotations. Consider the following relationship between Student and Course entity.

 According to the relationship a student can enroll in any number of courses and the course can have any number of students.

To create this relationship you need to have a STUDENT, COURSE and STUDENT_COURSE table. The relational model is shown below.

To create the STUDENT, COURSE and STUDENT_COURSE table you need to create the following Java Class files.

Student class is used to create the STUDENT and STUDENT_COURSE table.

01.package com.vaannila.student;

02. 

03.import java.util.HashSet;

04.import java.util.Set;

05. 

06.import javax.persistence.CascadeType;

07.import javax.persistence.Column;

08.import javax.persistence.Entity;

09.import javax.persistence.GeneratedValue;

10.import javax.persistence.Id;

11.import javax.persistence.JoinColumn;

12.import javax.persistence.JoinTable;

13.import javax.persistence.ManyToMany;

14.import javax.persistence.Table;

15. 

16.@Entity

17.@Table(name = "STUDENT")

18.public class Student {

19. 

20.private long studentId;

21.private String studentName;

22.private Set<Course> courses = new HashSet<Course>(0);

23. 

24.public Student() {

25.}

26. 

27.public Student(String studentName) {

28.this.studentName = studentName;

29.}

30. 

31.public Student(String studentName, Set<Course> courses) {

32.this.studentName = studentName;

33.this.courses = courses;

34.}

35. 

36.@Id

37.@GeneratedValue

38.@Column(name = "STUDENT_ID")

39.public long getStudentId() {

40.return this.studentId;

41.}

42. 

43.public void setStudentId(long studentId) {

44.this.studentId = studentId;

45.}

46. 

47.@Column(name = "STUDENT_NAME", nullable = false, length = 100)

48.public String getStudentName() {

49.return this.studentName;

50.}

51. 

52.public void setStudentName(String studentName) {

53.this.studentName = studentName;

54.}

55. 

56.@ManyToMany(cascade = CascadeType.ALL)

57.@JoinTable(name = "STUDENT_COURSE", joinColumns = { @JoinColumn(name ="STUDENT_ID") }, inverseJoinColumns = { @JoinColumn(name ="COURSE_ID") })

58.public Set<Course> getCourses() {

59.return this.courses;

60.}

61. 

62.public void setCourses(Set<Course> courses) {

63.this.courses = courses;

64.}

65. 

66.}

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