多对多单向，一个学生可以有多个老师，一个老师也可以教多个学生。老师可以找到他的学生，学生找不到教他的老师。
老师类Teacher：
package com.oracle.hibernate; import java.util.HashSet;
import java.util.Set; import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinColumns;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Table; @Entity
public class Teacher { private int id;
private String name;
//用set集合，不重复。因为表里的记录也不会重复
private Set<Student> students = new HashSet<Student>(); @Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
/**
* 多对多单向，会生成一张中间表，默认名字为Teacher_student，
* 默认的列名为teacher_id，students_id，
* @JoinTable修改中间表名、属性名
* name="t_s" 指定中间表名字
* 中间表只有学生id和老师id，
* joinColumns指定当前（Teacher类）的表的id
* inverseJoinColumns，逆转的，对方的，指定对方那张表对应的外键的id
*/
@ManyToMany
@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;
} public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
} }
学生类Student：
package com.oracle.hibernate; import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne; @Entity
public class Student { private int id;
private String name; @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;
} }
生成的表：
hibernate生成表的语句：
create table Student (
id integer not null auto_increment,
name varchar(255),
primary key (id)
)
create table Teacher (
id integer not null auto_increment,
name varchar(255),
primary key (id)
)
create table t_s (
teacher_id integer not null,
student_id integer not null,
primary key (teacher_id, student_id)
)
alter table t_s
add index FK1BF68372EF01B (teacher_id),
add constraint FK1BF68372EF01B
foreign key (teacher_id)
references Teacher (id)
alter table t_s
add index FK1BF682693A57B (student_id),
add constraint FK1BF682693A57B
foreign key (student_id)
references Student (id)
生成了Student表和Teacher表和中间表 t_s，列名也和自己设置的一样。