2011-07-04 6:52
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！
hibernate annotation多对多中间表添加其他字段的第三种方法
本示例主要以学生（T_Student）和课程（T_Course）之间的多对多关系，中间表Score（分数），学生表和课程表是多对多关系，另外为他们的关系添加额外的字段---
分数：
T_Student类如下：
package server.com.upc.test;
import Java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.MapKey;
@Entity
public class T_Student {
private int id;
private String name;
private Map<String,T_Crouse> course=
new HashMap<String,T_Crouse>
();
/*
* 或者
* private Set<T_Crouse> course=new HashSet<T_Crouse>();
*
* */
@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;
}
/*
* 或者
* @ManyToMany
@JoinTable(
name="score",
joinColumns=@JoinColumn(name="student_id"),
inverseJoinColumns=@JoinColumn(name="course_id")
)
*
*/
@ManyToMany
@MapKey(name="id"
)
@JoinTable(
name="score"
,
joinColumns=@JoinColumn(name="student_id"
),
inverseJoinColumns=@JoinColumn(name="course_id"
)
)
public Map<String, T_Crouse>
getCourse() {
return course;
}
public void setCourse(Map<String, T_Crouse>
course) {
this.course =
course;
}
}
T_course类：
package server.com.upc.test;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@Entity
public class T_Crouse {
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;
}
}
中间表Score也写成实体类：
package server.com.upc.test;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
@Entity
@Table(name="score"
)
public class T_Score {
private int id;
private int scrores;
private T_Student student;
private T_Crouse course;
@Id
@GeneratedValue
public int getId() {
return id;
}
public int getScrores() {
return scrores;
}
public void setScrores(
int scrores) {
this.scrores =
scrores;
}
public void setId(
int id) {
this.id =
id;
}
@ManyToOne
@JoinColumn(name="student_id"
)
public T_Student getStudent() {
return student;
}
public void setStudent(T_Student student) {
this.student =
student;
}
@ManyToOne
@JoinColumn(name="course_id"
)
public T_Crouse getCourse() {
return course;
}
public void setCourse(T_Crouse course) {
this.course =
course;
}
}
注意的是中间表中的导航关系manytomany @JoinColumn(name="course_id")；@JoinColumn(name="course_id")中声明的course_id，student_id和T_student表中声明的要一致,不然会产生其他的字段--再就是中间表的@Table(name="score"
)score名字和T_Student中的 @JoinTable(
name="score"
,要一样！！！
建立好之后就会生成中间表含有字段id，student_id,course_id，和score四个字段（然后hibernate生成的主键是（student_id,coure_id））虽然你在T_Score表中声明了自己的id。。。。这是值得注意的地方！
转载于:https://www.cnblogs.com/mjbrian/p/6873113.html
相关资源：JAVA上百实例源码以及开源项目
