Hibernate中多对多的annotation的写法（中间表可以有多个字段）

最新推荐文章于 2021-04-23 18:59:53 发布

转载最新推荐文章于 2021-04-23 18:59:53 发布 · 450 阅读

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本文介绍Hibernate中多对多关系的两种映射方式：一种仅用于关联，使用ManyToMany注解；另一种包含额外信息，需定义中间实体并采用一对多双向映射。

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一般情况下，多对多的关联关系是需要中间表的；

情况一：如果中间表仅仅是做关联用的，它里面仅有2个外键做联合主键，则使用ManyToMany（不用写中间表的Model，只需要写出两张主表的model即可）

学生表

@Entity
@Table(name = "T_STUDENT")
@SequenceGenerator(name = "SEQ_STUDENT", sequenceName = "SEQ_STUDENT")
public class Student implements Serializable {
private static final long serialVersionUID = 2524659555729848644L;
private Long id;
private String name;
private Date birthday;
private int sex;
private String address;
private Set<Teacher> teacherList;
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_STUDENT")
@Column(name = "ID", nullable = false, precision = 22, scale = 0)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(name = "NAME")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Temporal(TemporalType.DATE)
@Column(name = "BIRTHDAY")
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Column(name = "sex")
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
@Column(name = "address")
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "T_TEACHER_STUDENT",
joinColumns = @JoinColumn(name = "student_id"),
inverseJoinColumns = @JoinColumn(name = "teacher_id"))
public Set<Teacher> getTeacherList() {
return teacherList;
}
public void setTeacherList(Set<Teacher> teacherList) {
this.teacherList = teacherList;
}
}

教师表

@Entity
@Table(name = "T_TEACHER")
@SequenceGenerator(name = "SEQ_TEACHER", sequenceName = "SEQ_TEACHER")
public class Teacher implements Serializable {
private static final long serialVersionUID = 2297316923535111793L;
private Long id;
private String name;
private int sex;
private Set<Student> studentList;
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_TEACHER")
@Column(name = "ID", nullable = false, precision = 22, scale = 0)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(name = "name")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Column(name = "sex")
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
@ManyToMany(mappedBy = "teacherList", cascade = CascadeType.ALL)
public Set<Student> getStudentList() {
return studentList;
}
public void setStudentList(Set<Student> studentList) {
this.studentList = studentList;
}
}

hibernate.cfg.xml配置2个class类

<mapping class="com.dvn.li.model.Student"/>
<mapping class="com.dvn.li.model.Teacher"/>

测试：

SessionFactory sessionFactory = null;
Session session = null;
try {
sessionFactory = HibernateUtil.getSessionFactory();
session = sessionFactory.getCurrentSession();
session.beginTransaction();
Student s = new Student();
s.setName("小猪");
Teacher t = new Teacher();
t.setName("小李");
Set<Teacher> t_set = new HashSet<Teacher>();
t_set.add(t);
s.setTeacherList(t_set);
session.save(s);

} catch (Exception e) {
if (session != null) {
session.getTransaction().rollback();
}
}

测试通过！！！

很简单吧！注意HibernateUtil.getSessionFactory()的实现如下：

public class HibernateUtil {
private static final SessionFactory sessionFactory;

static {
try {
// Create the SessionFactory from hibernate.cfg.xml
sessionFactory = new AnnotationConfiguration().configure()
.buildSessionFactory();
} catch (Throwable ex) {
// Make sure you log the exception, as it might be swallowed
System.err.println("Initial SessionFactory creation failed." + ex);
throw new ExceptionInInitializerError(ex);
}
}

public static SessionFactory getSessionFactory() {
return sessionFactory;
}
}

如果自己做测试，可以通过SchemaExport导入表结构

SchemaExport export = new SchemaExport(new AnnotationConfiguration()
.configure());
export.create(true, true);

情况二：如果中间表不仅仅是做关联用的，它里面包含了其他字段信息，仅仅靠多对多的关系是搞不定的。

解决方案：多对多的关系拆分为两个一对多！这时候三张表的Model都需要写。

我们知道，一对多的关系，一般都是在多的一方做配置。具体代码如下：

学生表

@Entity
@Table(name = "T_STUDENT")
@SequenceGenerator(name = "SEQ_STUDENT", sequenceName = "SEQ_STUDENT")
public class Student2 implements Serializable {
private static final long serialVersionUID = 2524659555729848644L;
private Long id;
private String name;
private Date birthday;
private int sex;
private String address;
private Set<TeacherStudent> teacherStudentList;
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_STUDENT")
@Column(name = "ID", nullable = false, precision = 22, scale = 0)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(name = "NAME")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Temporal(TemporalType.DATE)
@Column(name = "BIRTHDAY")
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Column(name = "sex")
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
@Column(name = "address")
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@OneToMany(mappedBy="student",cascade=CascadeType.ALL)
public Set<TeacherStudent> getTeacherStudentList() {
return teacherStudentList;
}
public void setTeacherStudentList(Set<TeacherStudent> teacherStudentList) {
this.teacherStudentList = teacherStudentList;
}
}

教师表

@Entity
@Table(name = "T_TEACHER")
@SequenceGenerator(name = "SEQ_TEACHER", sequenceName = "SEQ_TEACHER")
public class Teacher2 implements Serializable {
private static final long serialVersionUID = 2297316923535111793L;
private Long id;
private String name;
private int sex;
private Set<TeacherStudent> teacherStudentList;
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_TEACHER")
@Column(name = "ID", nullable = false, precision = 22, scale = 0)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(name = "name")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Column(name = "sex")
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
@OneToMany(mappedBy = "teacher",cascade=CascadeType.ALL)
public Set<TeacherStudent> getTeacherStudentList() {
return teacherStudentList;
}
public void setTeacherStudentList(Set<TeacherStudent> teacherStudentList) {
this.teacherStudentList = teacherStudentList;
}
}

中间表

@Entity
@Table(name = "T_TEACHERSTUDENT")
@SequenceGenerator(name = "SEQ_TEACHERSTUDENT", sequenceName = "SEQ_TEACHERSTUDENT")
public class TeacherStudent implements Serializable {
private Long id;
private Student2 student;
private Teacher2 teacher;
private String note1;
private String note2;
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_TEACHERSTUDENT")
@Column(name = "ID", nullable = false, precision = 22, scale = 0)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(name = "note1")
public String getNote1() {
return note1;
}
public void setNote1(String note1) {
this.note1 = note1;
}
@Column(name = "note2")
public String getNote2() {
return note2;
}
public void setNote2(String note2) {
this.note2 = note2;
}
@ManyToOne(cascade=CascadeType.ALL)
@JoinColumn(name = "student_id", unique = true)
public Student2 getStudent() {
return student;
}
public void setStudent(Student2 student) {
this.student = student;
}
@ManyToOne
@JoinColumn(name = "teacher_id", unique = true)
public Teacher2 getTeacher() {
return teacher;
}
public void setTeacher(Teacher2 teacher) {
this.teacher = teacher;
}
}

hibernate.cfg.xml 引入对象

<mapping class="com.dvn.li.model.Student2"/>
<mapping class="com.dvn.li.model.Teacher2"/>
<mapping class="com.dvn.li.model.TeacherStudent"/>

测试：

SessionFactory sessionFactory = null;
Session session = null;
try {
sessionFactory = HibernateUtil.getSessionFactory();
session = sessionFactory.getCurrentSession();
session.beginTransaction();
Student2 s = new Student2();
s.setName("小猪");
Teacher2 t = new Teacher2();
t.setName("小李");
TeacherStudent ts=new TeacherStudent();
ts.setStudent(s);
ts.setTeacher(t);
ts.setNote1("以呀呀！！！");
session.save(s);
session.save(t);
session.save(ts);
session.getTransaction().commit();
} catch (Exception e) {
if (session != null) {
session.getTransaction().rollback();
}
}

测试通过！