hibernate的多对多双向外键关联

import javax.persistence.Entity;  
import javax.persistence.GeneratedValue;  
import javax.persistence.Id;  
import javax.persistence.ManyToOne;  
import javax.persistence.Table;  

@Entity  
@Table(name="t_student")  
public class Student{  

    private int id;  
    private String name;  
    private Set<Teacher> teachers;

    @ManyToMany(mappedBy="students")
    public Set<Teacher> getTeachers() {  
        return teachers;  
    }  
    public void setTeachers(Set<Teacher> teachers) {  
        this.teachers= teachers;  
    }  

    @Id  
    @GeneratedValue  
    public int getId() {  
        return id;  
    }  
    public void setId(int id) {  
        this.id = id;  
    }  
    public String getName() {  
        return name;  
    }  
    public void setName(String name) {  
        this.name = name;  
    }  

}  

import javax.persistence.Entity;  
import javax.persistence.GeneratedValue;  
import javax.persistence.Id;  
import javax.persistence.ManyToOne;  
import javax.persistence.Table;  

@Entity  
@Table(name="t_teacher")  
public class Teacher{  

    private int id;  
    private String name; 
    pricate Set<Student> students; 


    @ManyToMany(cascade = CascadeType.REFRESH, fetch = FetchType.EAGER)
    @JoinTable(name = "t_s", joinColumns = @JoinColumn(name = "teacher_id"),
            inverseJoinColumns = @JoinColumn(name = "student_id"))
    public Set<Student> getStudents() {  
        return students;  
    }  
    public void setStudents(Set<Student> students) {  
        this.students= students;  
    }  
    @Id  
    @GeneratedValue  
    public int getId() {  
        return id;  
    }  
    public void setId(int id) {  
        this.id = id;  
    }  
    public String getName() {  
        return name;  
    }  
    public void setName(String name) {  
        this.name = name;  
    }  

}  

数据库的结构和单向关联的没有什么区别