实体关系之@ManyToMany

1. packagecom.entity;
3. importjava.io.Serializable;
4. importjava.util.HashSet;
5. importjava.util.Set;
7. importjavax.persistence.Column;
8. importjavax.persistence.Entity;
9. importjavax.persistence.GeneratedValue;
10. importjavax.persistence.Id;
11. importjavax.persistence.ManyToMany;
12. importjavax.persistence.Table;
14. @Entity
15. @Table(name="Student")
16. publicclassStudentimplementsSerializable{
18. privateIntegerstudentid;//学生ID
19. privateStringstudentName;//学生姓名
20. privateSet<Teacher>teachers=newHashSet<Teacher>();//对应的教师集合
22. publicStudent(){
23. }
25. publicStudent(StringstudentName){
26. this.studentName=studentName;
27. }
29. @Id
30. @GeneratedValue
31. publicIntegergetStudentid(){
32. returnstudentid;
33. }
35. publicvoidsetStudentid(Integerstudentid){
36. this.studentid=studentid;
37. }
39. @Column(nullable=false,length=32)
40. publicStringgetStudentName(){
41. returnstudentName;
42. }
44. publicvoidsetStudentName(StringstudentName){
45. this.studentName=studentName;
46. }
48. /*
49. *@ManyToMany注释表示Student是多对多关系的一边，mappedBy属性定义了Student为双向关系的维护端
50. */
51. @ManyToMany(mappedBy="students")
52. publicSet<Teacher>getTeachers(){
53. returnteachers;
54. }
56. publicvoidsetTeachers(Set<Teacher>teachers){
57. this.teachers=teachers;
58. }
59. }

Teacher.java

Java代码

1. packagecom.entity;
3. importjava.io.Serializable;
4. importjava.util.HashSet;
5. importjava.util.Set;
7. importjavax.persistence.CascadeType;
8. importjavax.persistence.Column;
9. importjavax.persistence.Entity;
10. importjavax.persistence.FetchType;
11. importjavax.persistence.GeneratedValue;
12. importjavax.persistence.Id;
13. importjavax.persistence.JoinTable;
14. importjavax.persistence.ManyToMany;
15. importjavax.persistence.Table;
16. importjavax.persistence.JoinColumn;
18. @Entity
19. @Table
20. publicclassTeacherimplementsSerializable{
22. privateIntegerteacherid;//教师ID
23. privateStringteacherName;//教师姓名
24. privateSet<Student>students=newHashSet<Student>();//对应的学生集合
26. publicTeacher(){
28. }
30. publicTeacher(StringteacherName){
31. this.teacherName=teacherName;
32. }
34. @Id
35. @GeneratedValue
36. publicIntegergetTeacherid(){
37. returnteacherid;
38. }
40. publicvoidsetTeacherid(Integerteacherid){
41. this.teacherid=teacherid;
42. }
44. @Column(nullable=false,length=32)
45. publicStringgetTeacherName(){
46. returnteacherName;
47. }
49. publicvoidsetTeacherName(StringteacherName){
50. this.teacherName=teacherName;
51. }
52. /*
53. *@ManyToMany注释表示Teacher是多对多关系的一端。
54. *@JoinTable描述了多对多关系的数据表关系，name属性指定中间表名称。
55. *joinColumns定义中间表与Teacher表的外键关系，中间表Teacher_Student的Teacher_ID列是Teacher表的主键列对应的外键列。
56. *inverseJoinColumns属性定义了中间表与另外一端(Student)的外键关系。
57. */
58. @ManyToMany(cascade=CascadeType.PERSIST,fetch=FetchType.LAZY)
59. @JoinTable(name="Teacher_Student",
60. joinColumns={@JoinColumn(name="teacher_ID",referencedColumnName="teacherid")},
61. inverseJoinColumns={@JoinColumn(name="student_ID",referencedColumnName="studentid")
62. })
63. publicSet<Student>getStudents(){
64. returnstudents;
65. }
67. publicvoidsetStudents(Set<Student>students){
68. this.students=students;
69. }
71. publicvoidaddStudent(Studentstudent){
72. if(!this.students.contains(student)){//检测在该散列表中某些键是否映射到指定值,value查找的值。如果某些键映射到该散列表中的值为true，否则false
73. this.students.add(student);
74. }
75. }
77. publicvoidremoveStudent(Studentstudent){
78. this.students.remove(student);
79. }
81. }

转自：http://lym6520.iteye.com/blog/314065