以前在使用hibernate的時(shí)候，對(duì)“多對(duì)多”關(guān)聯(lián)產(chǎn)生的關(guān)聯(lián)表中數(shù)據(jù)修改起來(lái)很費(fèi)盡，寫這篇文章的目的是針對(duì)雙向關(guān)聯(lián)的多對(duì)多關(guān)系的關(guān)系表數(shù)據(jù)進(jìn)行方便的增刪的操作。如果各位高人已經(jīng)有了更好的方法，請(qǐng)不吝賜教。
首先，我們定義兩個(gè)實(shí)體。
Teacher和Student。它們是雙向的多對(duì)多關(guān)系，Teacher是關(guān)系的維護(hù)端，Student是關(guān)系的被維護(hù)端。代碼如下：
Teacher實(shí)體：
package com.wish.test.model;
import java.util.HashMap;
import java.util.Map;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Entity
@Table(name = "t_teacher")
public class Teacher implements java.io.Serializable
{
/**
*
*/
private static final long serialVersionUID = -8291865074665564287L;
@Id
@Column(name = "TeacherCode", length = 50)
private String teacherCode;
@Column(name = "TeacherName", length = 50)
private String teacherName;
@ManyToMany(mappedBy = "teachers", cascade = CascadeType.ALL)
private Map<String,Student> students = new HashMap<String,Student>();
public String getTeacherCode()
{
return teacherCode;
}
public void setTeacherCode(String teacherCode)
{
this.teacherCode = teacherCode;
}
public String getTeacherName()
{
return teacherName;
}
public void setTeacherName(String teacherName)
{
this.teacherName = teacherName;
}
public Map<String,Student> getStudents()
{
return students;
}
public void setStudents(Map<String,Student> students)
{
this.students = students;
}
public void addStudent(Student student)
{
if(!students.containsKey(student.getStudentCode()))
{
students.put(student.getStudentCode(), student);
}
}
public void removeStudent(Student student)
{
if(students.containsKey(student.getStudentCode()))
{
students.remove(student.getStudentCode());
System.out.println("remove student:" + student.getStudentName());
}
}
}
Student實(shí)體：
package com.wish.test.model;
import java.util.HashMap;
import java.util.Map;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Entity
@Table(name = "t_student")
public class Student implements java.io.Serializable
{
/**
*
*/
private static final long serialVersionUID = 9088096011898259042L;
@Id
@Column(name = "StudentCode", length = 50)
private String studentCode;
@Column(name = "StudentName", length = 50)
private String studentName;
@ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
@JoinTable(name = "t_student_teacher",
joinColumns = { @JoinColumn(name = "StudentCode", referencedColumnName = "studentCode") },
inverseJoinColumns = { @JoinColumn(name = "TeacherCode", referencedColumnName = "teacherCode") })
private Map<String,Teacher> teachers = new HashMap<String,Teacher>();
public String getStudentCode()
{
return studentCode;
}
public void setStudentCode(String studentCode)
{
this.studentCode = studentCode;
}
public String getStudentName()
{
return studentName;
}
public void setStudentName(String studentName)
{
this.studentName = studentName;
}
public Map<String,Teacher> getTeachers()
{
return teachers;
}
public void setTeachers(Map<String,Teacher> teachers)
{
this.teachers = teachers;
}
public void addTeacher(Teacher teacher)
{
if(!teachers.containsKey(teacher.getTeacherCode()))
{
this.teachers.put(teacher.getTeacherCode(), teacher);
}
}
public void removeTeacher(Teacher teacher)
{
if(teachers.containsKey(teacher.getTeacherCode()))
{
teachers.remove(teacher.getTeacherCode());
System.out.println("remove teacher:" + teacher.getTeacherName());
}
}
}
大家注意到Teacher和Student兩個(gè)實(shí)體中都包含了添加和刪除學(xué)生（教師）的方法：addStudent和removeStudent（addTeacher和removeTeacher），我們將用它們來(lái)進(jìn)行對(duì)管理表數(shù)據(jù)的添加和修改操作。
第二，我們定義dao層。
IStudentDao和ITeacherDao，代碼如下：
IStudentDao
package com.wish.test.dao;
import com.wish.test.model.Student;
public interface IStudentDao
{
public void insertStudent(Student student) throws RuntimeException;
public void updateStudent(Student student) throws RuntimeException;
public void deleteStudent(String studentCode) throws RuntimeException;
public Student getStudent(String studentCode) throws RuntimeException;
public Student loadTeachers(Student student) throws RuntimeException;
}
ITeacherDao
package com.wish.test.dao;
import com.wish.test.model.Teacher;
public interface ITeacherDao
{
public void insertTeacher(Teacher teacher) throws RuntimeException;
public void updateTeacher(Teacher teacher) throws RuntimeException;
public void deleteTeacher(String teacherCode) throws RuntimeException;
public Teacher getTeacher(String teacherCode) throws RuntimeException;
public Teacher loadStudents(Teacher teacher) throws RuntimeException;
}
它們的實(shí)現(xiàn)如下：
StudentDao
package com.wish.test.dao.impl;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import com.wish.test.dao.IStudentDao;
import com.wish.test.model.Student;
public class StudentDao implements IStudentDao
{
@PersistenceContext
private EntityManager em;
@Override
public void insertStudent(Student student) throws RuntimeException
{
em.persist(student);
}
@Override
public void deleteStudent(String studentCode) throws RuntimeException
{
em.remove(em.find(Student.class, studentCode));
}
@Override
public void updateStudent(Student student) throws RuntimeException
{
em.merge(student);
}
@Override
public Student getStudent(String studentCode) throws RuntimeException
{
return em.find(Student.class, studentCode);
}
@Override
public Student loadTeachers(Student student) throws RuntimeException
{
Student tempStudent = em.find(Student.class, student.getStudentCode());
if(tempStudent != null)
{
tempStudent.getTeachers().size();
}
return tempStudent;
}
}
TeacherDao
package com.wish.test.dao.impl;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import com.wish.test.dao.ITeacherDao;
import com.wish.test.model.Teacher;
public class TeacherDao implements ITeacherDao
{
@PersistenceContext
private EntityManager em;
@Override
public void insertTeacher(Teacher teacher) throws RuntimeException
{
em.persist(teacher);
}
@Override
public void deleteTeacher(String teacherCode) throws RuntimeException
{
em.remove(em.find(Teacher.class, teacherCode));
}
@Override
public void updateTeacher(Teacher teacher) throws RuntimeException
{
em.merge(teacher);
}
@Override
public Teacher getTeacher(String teacherCode) throws RuntimeException
{
return em.find(Teacher.class, teacherCode);
}
@Override
public Teacher loadStudents(Teacher teacher) throws RuntimeException
{
Teacher tempTeacher = em.find(Teacher.class, teacher.getTeacherCode());
if(tempTeacher != null)
{
tempTeacher.getStudents().size();
}
return tempTeacher;
}
}
第三，我們來(lái)定義Service層。
ITestService
package com.wish.test.service;
import com.wish.test.model.Student;
import com.wish.test.model.Teacher;
public interface ITestService
{
public void addStudent(Student student) throws RuntimeException;
public void modifyStudent(Student student) throws RuntimeException;
public void removeStudent(String studentCode) throws RuntimeException;
public void addTeacher(Teacher teacher) throws RuntimeException;
public void modifyTeacher(Teacher teacher) throws RuntimeException;
public void removeTeacher(String teacherCode) throws RuntimeException;
public Student getStudent(String studentCode) throws RuntimeException;
public Teacher getTeacher(String teacherCode) throws RuntimeException;
public Teacher loadStudents(Teacher teacher) throws RuntimeException;
public Student loadTeachers(Student student) throws RuntimeException;
}
其實(shí)現(xiàn)如下：
TestService
package com.wish.test.service.impl;
import org.springframework.transaction.annotation.Transactional;
import com.wish.test.dao.IStudentDao;
import com.wish.test.dao.ITeacherDao;
import com.wish.test.model.Student;
import com.wish.test.model.Teacher;
import com.wish.test.service.ITestService;
public class TestService implements ITestService
{
IStudentDao studentDao = null;
ITeacherDao teacherDao = null;
public TestService(IStudentDao studentDao, ITeacherDao teacherDao)
{
this.studentDao = studentDao;
this.teacherDao = teacherDao;
}
@Override
@Transactional(readOnly = false)
public void addStudent(Student student) throws RuntimeException
{
studentDao.insertStudent(student);
}
@Override
@Transactional(readOnly = false)
public void addTeacher(Teacher teacher) throws RuntimeException
{
teacherDao.insertTeacher(teacher);
}
@Override
@Transactional(readOnly = false)
public void removeStudent(String studentCode) throws RuntimeException
{
studentDao.deleteStudent(studentCode);
}
@Override
@Transactional(readOnly = false)
public void removeTeacher(String teacherCode) throws RuntimeException
{
teacherDao.deleteTeacher(teacherCode);
}
@Override
@Transactional(readOnly = false)
public void modifyStudent(Student student) throws RuntimeException
{
studentDao.updateStudent(student);
}
@Override
@Transactional(readOnly = false)
public void modifyTeacher(Teacher teacher) throws RuntimeException
{
teacherDao.updateTeacher(teacher);
}
@Override
@Transactional(readOnly = true)
public Student getStudent(String studentCode) throws RuntimeException
{
return studentDao.getStudent(studentCode);
}
@Override
@Transactional(readOnly = true)
public Teacher getTeacher(String teacherCode) throws RuntimeException
{
return teacherDao.getTeacher(teacherCode);
}
@Override
@Transactional(readOnly = true)
public Teacher loadStudents(Teacher teacher) throws RuntimeException
{
return teacherDao.loadStudents(teacher);
}
@Override
@Transactional(readOnly = true)
public Student loadTeachers(Student student) throws RuntimeException
{
return studentDao.loadTeachers(student);
}
}
第四，我們來(lái)定義調(diào)用service層的javabean，TestManage。
代碼如下：
package com.wish.test.bean;
import org.apache.log4j.Logger;
import com.wish.spring.tools.SpringBeanController;
import com.wish.test.model.Student;
import com.wish.test.model.Teacher;
import com.wish.test.service.ITestService;
public class TestManage
{
private ITestService testService = (ITestService)SpringBeanController.getBean("testService");
private static Logger log = Logger.getLogger(TestManage.class);
public boolean addStudent(Student student)
{
try
{
testService.addStudent(student);
return true;
}
catch (RuntimeException e)
{
log.error(e.toString());
return false;
}
}
public boolean modifyStudent(Student student)
{
try
{
testService.modifyStudent(student);
return true;
}
catch (RuntimeException e)
{
log.error(e.toString());
return false;
}
}
public boolean removeStudent(String studentCode)
{
try
{
testService.removeStudent(studentCode);
return true;
}
catch (RuntimeException e)
{
log.error(e.toString());
return false;
}
}
public boolean addTeacher(Teacher teacher)
{
try
{
testService.addTeacher(teacher);
return true;
}
catch (RuntimeException e)
{
log.error(e.toString());
return false;
}
}
public boolean modifyTeacher(Teacher teacher)
{
try
{
testService.modifyTeacher(teacher);
return true;
}
catch (RuntimeException e)
{
log.error(e.toString());
return false;
}
}
public boolean removeTeacher(String teacherCode)
{
try
{
testService.removeTeacher(teacherCode);
return true;
}
catch (RuntimeException e)
{
log.error(e.toString());
return false;
}
}
public Student getStudent(String studentCode)
{
try
{
return testService.getStudent(studentCode);
}
catch (RuntimeException e)
{
log.error(e.toString());
return null;
}
}
public Teacher getTeacher(String teacherCode)
{
try
{
return testService.getTeacher(teacherCode);
}
catch (RuntimeException e)
{
log.error(e.toString());
return null;
}
}
public Teacher loadStudents(Teacher teacher)
{
try
{
return testService.loadStudents(teacher);
}
catch (RuntimeException e)
{
log.error(e.toString());
return null;
}
}
public Student loadTeachers(Student student)
{
try
{
return testService.loadTeachers(student);
}
catch (RuntimeException e)
{
log.error(e.toString());
return null;
}
}
}
最后，我們?cè)贘SP頁(yè)面中調(diào)用javabean中的方法。
test.jsp，這些方法可以實(shí)現(xiàn)對(duì)雙向多對(duì)多關(guān)聯(lián)表數(shù)據(jù)的單條增刪操作。
代碼如下：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<jsp:useBean id="test" class="com.wish.test.bean.TestManage" scope="request"></jsp:useBean>
<%@page import="com.wish.test.model.Student"%>
<%@page import="com.wish.test.model.Teacher"%>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title></title>
</head>
<body>
<%
/**********************************************************************************
* 說(shuō)明： *
* Student 和 Teacher 為兩個(gè)實(shí)體，為多對(duì)多關(guān)系； *
* Teacher 為關(guān)系的維護(hù)端，Student為被維護(hù)端； *
* Teacher 與 Student 為級(jí)聯(lián)添加關(guān)系； *
* 在Student存在addTeacher和removeTeacher方法； *
* 在Teacher存在addStudent和removeStudent方法； *
* 兩個(gè)實(shí)體在數(shù)據(jù)庫(kù)中對(duì)應(yīng)的表中各存在10條記錄，無(wú)關(guān)聯(lián)數(shù)據(jù) *
***********************************************************************************/
/* 添加關(guān)聯(lián) */
/* 從維護(hù)端添加與被維護(hù)端的關(guān)聯(lián)
Teacher t = test.getTeacher("teacher01");
Student s1 = test.getStudent("student01");
Student s2 = test.getStudent("student02");
t = test.loadStudents(t);
s1 = test.loadTeachers(s1);
s2 = test.loadTeachers(s2);
t.addStudent(s1);
t.addStudent(s2);
s1.addTeacher(t);
s2.addTeacher(t);
test.modifyTeacher(t);
*/
/* 從被維護(hù)端添加與維護(hù)端的關(guān)聯(lián)
Student s = test.getStudent("student03");
Teacher t2 = test.getTeacher("teacher02");
Teacher t3 = test.getTeacher("teacher03");
s = test.loadTeachers(s);
t2 = test.loadStudents(t2);
t3 = test.loadStudents(t3);
s.addTeacher(t2);
s.addTeacher(t3);
t2.addStudent(s);
t3.addStudent(s);
test.modifyStudent(s);
*/
/* 刪除關(guān)聯(lián) */
/* 從維護(hù)端刪除與被維護(hù)端的關(guān)聯(lián)：目前這種對(duì)應(yīng)模式，無(wú)法從維護(hù)端單條刪除與被維護(hù)端的關(guān)聯(lián)
Teacher t = test.getTeacher("teacher01");
Student s1 = test.getStudent("student01");
Student s2 = test.getStudent("student02");
t = test.loadStudents(t);
t.removeStudent(s1);
test.modifyTeacher(t);
*/
/* 從被維護(hù)端刪除與維護(hù)端的關(guān)聯(lián)
Student s = test.getStudent("student03");
Teacher t2 = test.getTeacher("teacher02");
Teacher t3 = test.getTeacher("teacher03");
s = test.loadTeachers(s);
s.removeTeacher(t2);
//s.removeTeacher(t3);
test.modifyStudent(s);
*/
// 直接刪除維護(hù)端實(shí)體，關(guān)聯(lián)刪除了所有被維護(hù)端
//test.removeTeacher("teacher01");
// 直接刪除被維護(hù)端實(shí)體，可以刪除與維護(hù)端的關(guān)聯(lián)************
//test.removeStudent("student11");
// 總結(jié)：對(duì)于不經(jīng)常變動(dòng)的實(shí)體，在定義其多對(duì)多關(guān)聯(lián)時(shí)，盡量將其定義為被維護(hù)端，這樣對(duì)其增加和修改關(guān)聯(lián)時(shí)比較方便
%>
</body>
</html>
寫的比較基礎(chǔ)，請(qǐng)大家批評(píng)指正。
自己做程序員有快一年的時(shí)間了，其間經(jīng)歷的過(guò)程想必會(huì)對(duì)剛剛?cè)腴T的新手有些借鑒作用，因此準(zhǔn)備通過(guò)這個(gè)博客寫一些淺顯易懂的東西供新手參考，并希望高手給予指導(dǎo)。
多交流，勤交流。