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！