EJB3.0实例教程多对多和一对一
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EJB3.0开发之多对多和一对一
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 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 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 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 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 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 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 students1 = new HashSet(); Set students2 = new HashSet(); 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","smallnest@kuaff.com","男"); dao.create("朱","立焕","6","zhuzhu@kuaff.com","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。
