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发布时间:2016-01-01 作者:网络 阅读:178次
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。
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