教学管理系统-实体Bean

1.抽象基类

每个实体Bean都有一些类似的字段，例如id,version等，所以可以抽象出一个基类来。

package org.bnuitse.tms.model;

import java.io.Serializable;

import javax.persistence.MappedSuperclass;
import javax.persistence.Version;

@MappedSuperclass
public abstract class AbstractEntityBean implements IEntityBean, Serializable {
 private static final long serialVersionUID = 1L;

 protected int id;

 private int version;

 public AbstractEntityBean() {
 }

 public void setId(int id) {
  this.id = id;
 }

 @Version
 public int getVersion() {
  return version;
 }

 public void setVersion(int version) {
  this.version = version;
 }
}

@MappedSuperclass用于标识AbstractEntityBean中的数据字段也用于持久化。

IEntityBean是一个接口，用于会话Bean进行统一处理。见《教学管理系统-会话Bean》。

package org.bnuitse.tms.model;

public interface IEntityBean {
 int getId();
}

2.具体类

具体类需要定义从接口继承来的抽象方法getId()，原因是每个具体类对应数据库的主键名称、产生方式可能不同，需要在getId()方法上用@Column进行标识。

一对多数据，例如classes和depts，如果想要处理简单些，可以用Hibernate的DELETE_ORPHAN进行标识，具体含义见Hibernate文档。

一对多数据提供了addXxx和removeXxx方法，为的是进行aspect编程，见《教学管理系统-面向方面的编程》。

一对多数据通常是延迟加载。可以在查询语句中使用fetch加载lazy data。为了使用方便，自定义一个annotation称为@EagerlyFetchQuery，在会话Bean中会查找它，执行里面定义的查询。

private static final long serialVersionUID字段需要定义，原因有二：一是如果一个类实现Serializable接口,推荐定义该字段；二是当aspectj织入代码产生新类时，如果没有定义该字段，会自动生成一个新的serialVersionUID值(见java.io)，这样，UI从服务器端取出的数据和本地类的版本号不同，将产生异常。

package org.bnuitse.tms.model.security;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.TableGenerator;

import org.bnuitse.tms.model.AbstractEntityBean;
import org.bnuitse.tms.model.EagerlyFetchQuery;

@Entity
@Table(name = "org_college")
@EagerlyFetchQuery("from College o left join fetch o.classes left join fetch o.depts where o.id = :id")
public class College extends AbstractEntityBean {
 private static final long serialVersionUID = -8443100575405647610L;

 private String name;

 private List<CollegeClass> classes = new ArrayList<CollegeClass>();
 private List<CollegeDept> depts = new ArrayList<CollegeDept>();
 
 @Id
 @Column(name="collegeId")
 @TableGenerator(name = "CollegeGen", table = "pub_keygen", pkColumnName = "keyid", valueColumnName = "keyvalue", pkColumnValue = "College", allocationSize = 10, initialValue = 10000)
 @GeneratedValue(strategy = GenerationType.TABLE, generator = "CollegeGen")
 public int getId() {
  return id;
 }
 
 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 @OneToMany(mappedBy = "college", cascade = CascadeType.ALL)
 @org.hibernate.annotations.Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
 public List<CollegeClass> getClasses() {
  return classes;
 }

 public void setClasses(List<CollegeClass> classes) {
  this.classes = classes;
 }
 
 public void addClass(CollegeClass collegeClass) {
  collegeClass.setCollege(this);
  this.classes.add(collegeClass);
 }

 public void removeClass(CollegeClass collegeClass) {
  this.classes.remove(collegeClass);
 }
 
 @OneToMany(mappedBy = "college", cascade = CascadeType.ALL) 
 @org.hibernate.annotations.Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
 public List<CollegeDept> getDepts() {
  return depts;
 }

 public void setDepts(List<CollegeDept> depts) {
  this.depts = depts;
 }

 public void addDepartment(CollegeDept collegeDept) {
  collegeDept.setCollege(this);
  this.depts.add(collegeDept);
 }

 public void removeDepartment(CollegeDept collegeDept) {
  this.depts.remove(collegeDept);
 }
 
 public String toString() {
  return this.getId() + "-" + this.name;
 }
}