【Hibernate】之关于多对多双向关联映射
多对多的双向关联映射在项目实战中还是相当重要的，所以这里着重写一下！以学生表(Student)和老师表(Teacher)为例。
首先我们还是先看Annotations配置！
@Entity
@Table(name="t_student")
public class Student {
private Integer id;
private String name;
private Integer age;
private Set<Teacher> teachers=new HashSet<Teacher>();//指定从学生也可以映射老师
@ManyToMany(mappedBy="students")
public Set<Teacher>getTeachers() {
returnteachers;
}
publicvoidsetTeachers(Set<Teacher> teachers) {
this.teachers = teachers;
}
@Id
@GeneratedValue
public Integer getId() {
returnid;
}
publicvoid setId(Integerid) {
this.id = id;
}
@Column(name="s_name")
public String getName() {
returnname;
}
publicvoid setName(Stringname) {
this.name = name;
}
@Column(name="s_age")
public Integer getAge() {
returnage;
}
publicvoid setAge(Integerage) {
this.age = age;
}
}
@Entity
@Table(name="t_teacher")
public class Teacher {
private Integer id;
private String name;
private Set<Student> students=new HashSet<Student>();//set不允许重复，最适合数据库模型
@Id
@GeneratedValue
public Integer getId() {
returnid;
}
publicvoid setId(Integerid) {
this.id = id;
}
@Column(name="t_name")
public String getName() {
returnname;
}
publicvoid setName(Stringname) {
this.name = name;
}
@ManyToMany
@JoinTable(name="t_s_two",//自定义表名
joinColumns={@JoinColumn(name="teacher_id")},//自定义列名
inverseJoinColumns={@JoinColumn(name="student_id")})//反转，和Teacher对应的那个表的ID，也是自定义
public Set<Student>getStudents() {
returnstudents;
}
publicvoidsetStudents(Set<Student> students) {
this.students = students;
}
}JunitTest单元测试
@Test
publicvoid add(){
try {
Configuration cfg=new Configuration();
cfg.configure();
SessionFactory sessionFactory=cfg.buildSessionFactory();
Sessionsession=sessionFactory.openSession();
session.beginTransaction();
Student s=new Student();
s.setAge(12);
s.setName("张三");
session.save(s);
Student s2=new Student();
s2.setAge(13);
s2.setName("李四");
session.save(s2);
Teacher t=new Teacher();
t.setName("张老师");
Teacher t2=new Teacher();
t2.setName("李老师");
Set<Student>students=newHashSet<Student>();
students.add(s);
students.add(s2);
t.setStudents(students);
// Set<Teacher>teachers=new HashSet<Teacher>();
// teachers.add(t);
// teachers.add(t2);
// s.setTeacher(teachers);
// s2.setTeacher(teachers);
session.save(t);
session.save(t2);
session.getTransaction().commit();
sessionFactory.close();
} catch (HibernateException e){
e.printStackTrace();
}
}XML配置方法
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="csg.hibernate.entity"> <class name="Student" table="t_student"> <id name="id"> <column name="id"/> <generator class="native" /> </id> <property name="name" /> <property name="age" /> <set name="teachers" table="t_s_two"> <key column="student_id"/> <many-to-many class="csg.hibernate.entity.Teacher" column="Teacher_id"/> </set> </class> </hibernate-mapping>
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="csg.hibernate.entity"> <class name="Teacher" table="t_teacher"> <id name="id"> <column name="id"/> <generator class="native" /> </id> <property name="name" /> <set name="students" table="t_s_two"> <key column="teacher_id"/> <many-to-many class="csg.hibernate.entity.Student" column="student_id"/> </set> </class> </hibernate-mapping>
Ok，大家看到的其实就是将XML中的Set里面的值进行拷贝，修改， 需要注意的是
table和cloum都需要一致！这样建立的中间表才正规！
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原文：http://1936625305.blog.51cto.com/6410597/1568931