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。