Hibernate 多对多 中间表含有其他字段 注解方式实现

需求：

两个实体类：Teacher.class Student.class 中间表包含了一个额外字段：score

Teacher.calss

idname1Mr.zhang2Mr.wang

Student.class

idname1Xiaoming2Xiaohong

中间表

idteacher_idstudent_idscore1118921290
解决办法：

按照传统的多对多注解实现，中间表是以自身id为默认主键，另外包含了两个实体类的id，共3个字段，不能添加额外的字段。

解决办法是将ManyToMany 分解成两个OneToMany。

解决过程：

显示看到了这个blog：http://blog.csdn.net/liuxianbing119/article/details/7283769 知道这么处理，但是可以添加成功，删除一直不成功。

后来翻到了wiki里面的介绍：http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany

知道这种方法肯定没错，就又试了几次，终于成功了。

代码：

1. AbstractEntity.java

package com.cc.persistence;import java.io.Serializable;public abstract class AbstractEntity implements Persistable {public abstract Serializable getInternalId();@Overridepublic boolean equals(Object o) {if (o == null) return false;if (!o.getClass().getName().equals(this.getClass().getName())) return false;return ((Persistable)o).getInternalId().equals(this.getInternalId());}@Overridepublic int hashCode() {return this.getInternalId().hashCode();}}

2.Teacher.java

package com.xx;import java.io.Serializable;import java.util.Date;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;import javax.persistence.OneToMany;import javax.persistence.OrderBy;import javax.persistence.SequenceGenerator;import javax.persistence.Table;import javax.persistence.Transient;@Entity@Table(name = "teacher")public class Teacher extends AbstractEntity{/** *  */private static final long serialVersionUID = 2392788383432498751L;private Long id;private String name;private Set<TeacherStudent> teacherStudents;@Id@GeneratedValue(strategy = GenerationType.AUTO)public Long getId() {return id;}public void setId(Long id) {this.id = id;}@Column(name = "name", length = 256)public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToMany(mappedBy = "teacher")public Set<NoticeGroup> getTeacherStudents() {return teacherStudents;}public void setTeacherStudents(Set<TeacherStudent> teacherStudents) {this.teacherStudents = teacherStudents;}@Override@Transientpublic Serializable getInternalId() {return id;}}

3.Student.java

package com.xx;import java.io.Serializable;import java.util.Date;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;import javax.persistence.OneToMany;import javax.persistence.OrderBy;import javax.persistence.SequenceGenerator;import javax.persistence.Table;import javax.persistence.Transient;@Entity@Table(name = "student")public class Student extends AbstractEntity {/** *  */private static final long serialVersionUID = 6380182108640048430L;private Long id;private String name;private Set<TeacherStudent> teacherStudents;@Id@GeneratedValue(strategy = GenerationType.AUTO)public Long getId() {return id;}public void setId(Long id) {this.id = id;}@Column(length = 256)public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToMany(mappedBy = "student")public Set<TeacherStudent> TeacherStudents() {return teacherStudents;}public void setTeacherStudents(Set<TeacherStudent> teacherStudents) {this.teacherStudents = teacherStudents;}@Override@Transientpublic Serializable getInternalId() {return id;}}

4.TeacherStudent.java

package com.xx;import java.io.Serializable;import java.util.Date;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.Table;import javax.persistence.Transient;@Entity@Table(name = "teacher_student")public class TeacherStudent extends AbstractEntity {/** *  */private static final long serialVersionUID = 4876371202187846251L;private Long id;private Teacher teacher;private Student student;private Integer score; @Id@Column(name = "id", nullable = false)@GeneratedValue(strategy = GenerationType.AUTO)public Long getId() {return id;}public void setId(Long id) {this.id = id;}@ManyToOne@JoinColumn(name = "teacher_id")public Teacher getTeacher() {return teacher;}public void setTeacher(Teacher teacher) {this.teacher = teacher;}@ManyToOne@JoinColumn(name = "student_id")public Student getStudent() {return student;}public void setStudent(Student student) {this.student = student;}@Column(name="score")public Integer getScore() {return score;}public void setScore(Integer score) {this.score = score;}@Override@Transientpublic Serializable getInternalId() {// TODO Auto-generated method stubreturn id;}}

5.TeacherDaoImpl.java

   添加一个teacher-student 关系：

  

@Overridepublic boolean addStudentScore(Long teacherId,Long studentId,Integer score) {// TODO Auto-generated method stubStudent student = (Student) studentDao.findById(studentId);Session session = this.getSession();Transaction tx = null;try {tx = session.beginTransaction();Teacher teacher = (Teacher) session.get(getEntityClass(), teacherId);if (teacher != null && student != null) {//new TeacherStudentTeacherStudent ts = new TeacherStudent();ts.setTeacher(teacher);ts.setStudent(student);ts.setScore(score);session.save(ts);session.flush();tx.commit();return true;}} catch (Exception e) {if (tx != null)tx.rollback();} finally {session.close();}return false;}

删除一个teacher-student 关系：

@Overridepublic boolean removeStudentScore(Long teacherId,Long studentId) {// TODO Auto-generated method stubStudent student = (Student) studentDao.findById(studentId);Session session = this.getSession();Transaction tx = null;try {tx = session.beginTransaction();Teacher teacher = (Teacher) session.get(getEntityClass(), teacherId);Set<TeacherStudent> teacherStudents = null;if (teacher != null && student != null) {teacherStudents = teacher.getTeacherStudents();if (teacherStudents.size()>0){for(TeacherStudent teacherStudent:teacherStudents){if(teacherStudent.getStudent().getId().equals(studentId) && teacherStudent.getTeacher().getId().equals(teacherId)){session.delete(teacherStudent);}}}session.flush();tx.commit();return true;}} catch (Exception e) {if (tx != null)tx.rollback();} finally {session.close();}return false;}