EJB3.0开发指南:多对多和一对一

在前面的例子中，我们演示了一对多和多对一的例子，在本章将演示多对多和一对一的关系。

学生和老师就是多对多的关系。一个学生有多个老师，一个老师教多个学生。

学生和档案就是一对一的关系（不知道国外的学生有没有档案？）。

 为了实现多对多的关系，数据库中需要关联表，用以在两个实体间建立关联。JBoss可以自动生成关联表，你也可以@AssociationTable来指定关联表的信息。

如:

@ManyToMany(cascade = {CascadeType.CREATE, CascadeType.MERGE}, fetch = FetchType.EAGER, isInverse = true)

@AssociationTable(table = @Table(name = "STUDENT_TEACHER"),

        joinColumns = {@JoinColumn(name = "TEACHER_ID")},

        inverseJoinColumns = {@JoinColumn(name = "STUDENT_ID")})

 

@ AssociationTable的注释声明如下：

@Target({METHOD, FIELD})

public @interface AssociationTable {

Table table() default @Table(specified=false);

JoinColumn[] joinColumns() default {};

JoinColumn[] inverseJoinColumns() default {};

}

 

关联表注释指定了关联表的名称、主表的列和从表的列。

为了实现一对一的关系，需要用@OneToOne来注释。

如:

@OneToOne(cascade = {CascadeType.ALL})

    @JoinColumn(name = "DOSSIER_ID")

    public Dossier getDossier()

    {

        return dossier;

}

这定义了一个单向的一对一的关系。如果在Dossier也定义了相关的关联，那么它就是双向的。双向的意思就是通过一个Student实体就可以查找到一个Dossier，通过一个Dossier就可以查找到一个Student。

 

@ OneToOne的注释声明如下：

@Target({METHOD, FIELD}) @Retention(RUNTIME)

public @interface OneToOne {

String targetEntity() default "";

CascadeType[] cascade() default {};

FetchType fetch() default EAGER;

boolean optional() default true;

}

这个例子主要有以下几个文件，这个例子主要实现了学生和老师、学生和档案之间的关系。Student、Teacher、Dossier都是实体Bean。Student和Dossier是一个双向的OneToOne之间的关系，Student和Teacher是ManyToMany的关系，也是双向的。和前面的例子一样，我们还是使用Client测试。

Student.java：实体Bean。

Dossier.java：实体Bean所依赖的类。

Teacher.java：实体Bean所依赖的类。

EntityTest.java：会话Bean的业务接口

EntityTest Bean.java：会话Bean的实现类

Client.java：测试EJB的客户端类。

jndi.properties：jndi属性文件，提供访问jdni的基本配置属性。

Build.xml：ant 配置文件，用以编译、发布、测试、清除EJB。

下面针对每个文件的内容做一个介绍。

 

Student.java

package com.kuaff.ejb3.relationships;

 

import javax.ejb.CascadeType;

import javax.ejb.Entity;

import javax.ejb.FetchType;

import javax.ejb.GeneratorType;

import javax.ejb.Id;

import javax.ejb.JoinColumn;

import javax.ejb.OneToOne;

import javax.ejb.ManyToMany;

import javax.ejb.Table;

import javax.ejb.AssociationTable;

 

import java.util.ArrayList;

import java.util.Set;

import java.util.Collection;

import java.io.Serializable;

 

@Entity

@Table(name = "STUDENT")

public class Student implements Serializable

{

   

    private int id;

    private String first;

    private String last;

    private Dossier dossier;

    private Set<Teacher> teachers;

   

   

    @Id(generate = GeneratorType.AUTO)

    public int getId()

    {

       return id;

    }

 

    public void setId(int id)

    {

       this.id = id;

    }

   

  

 

    public void setFirst(String first)

    {

        this.first = first;

    }

 

    public String getFirst()

    {

        return first;

    }

 

    public void setLast(String last)

    {

        this.last = last;

    }

 

    public String getLast()

    {

        return last;

    }

 

    public void setDossier(Dossier dossier)

    {

        this.dossier = dossier;

    }

   

    @OneToOne(cascade = {CascadeType.ALL})

    @JoinColumn(name = "DOSSIER_ID")

    public Dossier getDossier()

    {

        return dossier;

    }

 

    public void setTeacher(Set<Teacher> teachers)

    {

        this.teachers = teachers;

    }

   

    @ManyToMany(cascade = {CascadeType.CREATE, CascadeType.MERGE}, fetch = FetchType.EAGER, isInverse = true)

    @AssociationTable(table = @Table(name = "STUDENT_TEACHER"),

        joinColumns = {@JoinColumn(name = "TEACHER_ID")},

        inverseJoinColumns = {@JoinColumn(name = "STUDENT_ID")})

    public Set<Teacher> getTeacher()

    {

        return teachers;

    }

 

  

   

  

}

 

Dossier.java

 

package com.kuaff.ejb3.relationships;

 

import javax.ejb.Entity;

import javax.ejb.GeneratorType;

import javax.ejb.Id;

 

@Entity

public class Dossier implements java.io.Serializable

{

    private Long id;

    private String resume;

 

    @Id(generate = GeneratorType.AUTO)

    public Long getId()

    {

       return id;

    }

 

    public void setId(Long id)

    {

       this.id = id;

    }

 

    public void setResume(String resume)

    {

        this.resume = resume;

    }

 

    public String getResume()

    {

        return resume;

    }

}

 

Teacher.java

 

package com.kuaff.ejb3.relationships;

 

import javax.ejb.AssociationTable;

import javax.ejb.Basic;

import javax.ejb.CascadeType;

import javax.ejb.Column;

import javax.ejb.Entity;

import javax.ejb.FetchType;

import javax.ejb.Id;

import javax.ejb.JoinColumn;

import javax.ejb.ManyToMany;

import javax.ejb.Table;

import javax.ejb.Transient;

import javax.ejb.Version;

import java.util.Set;

import javax.ejb.GeneratorType;

 

@Entity

public class Teacher implements java.io.Serializable

{

    private Long id;

 

    private String resume;

 

    private String name;

 

    private String info;

 

    private Set<Student> students;

 

    @Id(generate = GeneratorType.IDENTITY)

    public Long getId()

    {

        return id;

    }

 

    public void setId(Long id)

    {

        this.id = id;

    }

 

    public void setName(String name)

    {

        this.name = name;

    }

 

    public String getName()

    {

        return name;

    }

 

    public void setInfo(String info)

    {

        this.info = info;

    }

 

    public String getInfo()

    {

        return info;

    }

 

    public void setStudents(Set<Student> students)

    {

        this.students = students;

    }

   

    @ManyToMany(cascade = {CascadeType.CREATE, CascadeType.MERGE}, fetch = FetchType.EAGER)

    @AssociationTable(table = @Table(name = "STUDENT_TEACHER"),

    joinColumns = {@JoinColumn(name = "TEACHER_ID",referencedColumnName="ID")},

    inverseJoinColumns = {@JoinColumn(name = "STUDENT_ID",referencedColumnName="ID")})

    public Set<Student> getStudents()

    {

        return students;

    }

 

}

 

EntityTest.java

 

package com.kuaff.ejb3.relationships;

 

import javax.ejb.Remote;

import java.util.List;

 

@Remote

public interface EntityTest

{

    public void createData();

    public List findByName(String name);

}

 

EntityTestBean.java

 

package com.kuaff.ejb3.relationships;

 

import javax.ejb.EntityManager;

import javax.ejb.Inject;

import javax.ejb.Stateless;

 

import java.util.HashSet;

import java.util.Set;

import java.util.List;

 

@Stateless

public class EntityTestBean implements EntityTest

{

    private @Inject EntityManager manager;

   

    public void createData()

    {

        Teacher teacher1 = new Teacher();

        Teacher teacher2 = new Teacher();

       

        Set<Student> students1 = new HashSet<Student>();

        Set<Student> students2 = new HashSet<Student>();

       

        Student student1 = new Student();

        Student student2 = new Student();

        Student student3 = new Student();

               

        Dossier dossier1 = new Dossier();

        Dossier dossier2 = new Dossier();

        Dossier dossier3 = new Dossier();

       

        teacher1.setId(new Long(1));

        teacher1.setName("hushisheng");

        teacher1.setInfo("胡时胜教授，博士生导师");

        manager.create(teacher1);

        teacher2.setId(new Long(2));

        teacher2.setName("liyongchi");

        teacher2.setInfo("李永池教授，博士生导师");

        manager.create(teacher2);

       

        student1.setFirst("晁");

        student1.setLast("岳攀");

        dossier1.setResume("这是晁岳攀的档案");

        student1.setDossier(dossier1);

        students1.add(student1);

       

        student2.setFirst("赵");

        student2.setLast("志伟");

        dossier2.setResume("这是赵志伟的档案");

        student2.setDossier(dossier2);

        students1.add(student2);

       

        student3.setFirst("田");

        student3.setLast("明");

        dossier3.setResume("这是田明的档案");

        student3.setDossier(dossier3);

        students2.add(student3);

       

        teacher1.setStudents(students1);

        teacher2.setStudents(students2);

    }

    public List findByName(String name)

    {

        return manager.createQuery("from Teacher t where t.name = :name").setParameter("name", name).listResults();

    }

}

 

在这个会话Bean中提供了创建各个实体Bean的方法，并提供了查找老师的方法。

Client.java

 

package com.kuaff.ejb3.secondary;

 

import javax.naming.InitialContext;

import javax.naming.NamingException;

 

import java.util.List;

 

public class Client

{

 

    public static void main(String[] args) throws NamingException

    {

        InitialContext ctx = new InitialContext();

        StudentDAO dao = (StudentDAO) ctx.lookup(StudentDAO.class.getName());

        int id = dao.create("晁","岳攀","8","[email protected]","男");

        dao.create("朱","立焕","6","[email protected]","女");

       

        List list = dao.findAll();

        for(Object o:list)

        {

            Student s = (Student)o;

            System.out.printf("%s%s的性别:%s%n",s.getName().getFirst(),s.getName().getLast(),s.getGender());

            dao.evict(s);

        }

    }

}

 

这个客户端用来测试。

 

请运行{$JBOSS_HOME}/bin目录下的run.bat:  run –c all,启动JBOSS。

http://localhost:8080/jmx-console/HtmlAdaptor?action=inspectMBean&name=jboss%3Aservice%3DHypersonic%2Cdatabase%3DlocalDB，然后调用startDatabaseManager()方法，打开HSQL管理工具管理数据库。

 

在Eclipse的Ant视图中执行ejbjar target。或者在命令行下，进入到此工程目录下，执行ant ejbjar,将编译打包发布此EJB。

 

 

在Eclipse的Ant视图中执行run target。或者在命令行下，进入到此工程目录下，执行ant run,测试这个EJB。

本文地址：http://com.8s8s.com/it/it12573.htm