在应用Hibernate EntityManager进行多对多持久化时，运行TeacherManager时可以同时将Teacher,及Student数据都保存进数据库，可运行StudentManager时，却只能将Student数据保存，而Teacher数据并没有保存到数据库，为什么只能单向持久化，感觉只实现了一对多双向关联的功能，为此感到不解，请热心的大哥们帮忙解答，看我的代码是不是哪里写错了？谢谢。
以下是我的代码：
package com.landril.bean;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Entity
@Table(name = "Teacher")
public class Teacher implements Serializable {
private static final long serialVersionUID = 7772760144352800638L;
@Id
@GeneratedValue
private Integer teacherID;
private String teacherName;
@ManyToMany(cascade=CascadeType.PERSIST,fetch=FetchType.EAGER)
@JoinTable(name="Tea_Stud",
joinColumns={@JoinColumn(name="teacherID",referencedColumnName="teacherID")},
inverseJoinColumns={@JoinColumn(name="studentID",referencedColumnName="studentID")})
private Set<Student> students = new HashSet<Student>();
public Integer getTeacherID() {
return teacherID;
}
public void setTeacherID(Integer teacherID) {
this.teacherID = teacherID;
}
public String getTeacherName() {
return teacherName;
}
public void setTeacherName(String teacherName) {
this.teacherName = teacherName;
}
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
}
package com.landril.bean;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Entity
@Table(name = "Student")
public class Student implements Serializable {
private static final long serialVersionUID = -2778169665228730867L;
@Id
@GeneratedValue
private Integer studentID;
private String studentName;
@ManyToMany(mappedBy="students")
private Set<Teacher> teachers = new HashSet<Teacher>();
public Integer getStudentID() {
return studentID;
}
public void setStudentID(Integer studentID) {
this.studentID = studentID;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public Set<Teacher> getTeachers() {
return teachers;
}
public void setTeachers(Set<Teacher> teachers) {
this.teachers = teachers;
}
}
package com.landril.dao;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.EntityManager;
import com.landril.bean.Student;
import com.landril.bean.Teacher;
public class TeacherManager {
public static void main(String[] args) {
Teacher t = new Teacher();
Student s = new Student();
s.setStudentName("aa");
Student s1 = new Student();
// StudentManager sm = new StudentManager();
// Student s1 = sm.getStudent(2);
s1.setStudentName("bb");
Student s2 = new Student();
s2.setStudentName("cc");
Set<Student> ss = new HashSet<Student>();
ss.add(s);
ss.add(s1);
ss.add(s2);
t.setTeacherName("tt");
t.setStudents(ss);
Teacher t1 = new Teacher();
t1.setTeacherName("tt");
t1.setStudents(ss);
Teacher t2 = new Teacher();
t2.setTeacherName("tt");
t2.setStudents(ss);
TeacherManager tm = new TeacherManager();
tm.saveTeacher(t);
tm.saveTeacher(t1);
tm.saveTeacher(t2);
}
public void saveTeacher(Teacher tea){
EntityManager em = Manager.emf.createEntityManager();
em.getTransaction().begin();
em.persist(tea);
em.getTransaction().commit();
em.close();
}
public Teacher getTeacher(int id){
EntityManager em = Manager.emf.createEntityManager();
return em.find(Teacher.class, new Integer(id));
}
}
package com.landril.dao;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.EntityManager;
import com.landril.bean.Student;
import com.landril.bean.Teacher;
public class StudentManager {
public static void main(String[] args) {
// StudentManager sm = new StudentManager();
// Student s = sm.getStudent(2);
// System.out.println(s.getStudentName());
TeacherManager tm = new TeacherManager();
Teacher t1 = new Teacher();
t1.setTeacherName("t1");
Teacher t2 = new Teacher();
t2.setTeacherName("t2");
Teacher t3 = new Teacher();
t3.setTeacherName("t3");
// Teacher t1 = tm.getTeacher(1);
// Teacher t2 = tm.getTeacher(3);
// Teacher t3 = tm.getTeacher(5);
Set<Teacher> ts = new HashSet<Teacher>();
ts.add(t1);
ts.add(t2);
ts.add(t3);
Student s = new Student();
s.setStudentName("ssss");
s.setTeachers(ts);
StudentManager sm = new StudentManager();
sm.saveStudent(s);
}
public void saveStudent(Student s){
EntityManager em = Manager.emf.createEntityManager();
em.getTransaction().begin();
em.persist(s);
em.getTransaction().commit();
em.close();
}
public Student getStudent(int id){
EntityManager em = Manager.emf.createEntityManager();
return em.find(Student.class, 1);
}
}