无限级的双向一对多JPA映射(产品分类)
级联表
父类id 作为表的外键，外键指向到本身表的主键
类别实体bean定义
对象要在网络上传输必须先系列化
要进行对象之间的比较,所以要重载equals()、hashCode()
ProductType.java
package com.itcast.bean.product;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
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.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
//@Entity标注是一个实体bean
@Entity
public class ProductType implements Serializable{
private static final long serialVersionUID = -6826720065899410840L;
/** 类型id *对象标识，字符串类型用UUID生成出来，可以用数值类型 */
private Integer typeid;
/** 类型名称 **/
private String name;
/** 备注,用作Google搜索页面描述 **/
private String note;
/** 是否可见 **/
private Boolean visible=true;
/** 子类别 **/
private Set<ProductType> childtypes = new HashSet<ProductType>();
/** 所属父类 **/
private ProductType parent;
@Column(length=36,nullable=false)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Column(length=200)
public String getNote() {
return note;
}
public void setNote(String note) {
this.note = note;
}
@Column(nullable=false)
public Boolean getVisible() {
return visible;
}
public void setVisible(Boolean visible) {
this.visible = visible;
}
@Id @GeneratedValue(strategy=GenerationType.AUTO)
public Integer getTypeid() {
return typeid;
}
public void setTypeid(Integer typeid) {
this.typeid = typeid;
}
/**
* 根据JPA规范，双向关系要定义关系维护端和被维护端，在一的一端用mappedBy定义被维护端，指向维护段（多的一方）的外键
*/
@OneToMany(cascade={CascadeType.REFRESH,CascadeType.REMOVE},mappedBy="parent")
public Set<ProductType> getChildtypes() {
return childtypes;
}
public void setChildtypes(Set<ProductType> childtypes) {
this.childtypes = childtypes;
}
/**
* 可以用@JoinColumn()修改默认的关联外键字段名称
* optional属性定义这个对象是否对该字段赋值,true表示可以为空，默认为true
*/
@ManyToOne(cascade=CascadeType.REFRESH,optional=true)
@JoinColumn(name="parentid")
public ProductType getParent() {
return parent;
}
public void setParent(ProductType parent) {
this.parent = parent;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((typeid == null) ? 0 : typeid.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
final ProductType other = (ProductType) obj;
if (typeid == null) {
if (other.typeid != null)
return false;
} else if (!typeid.equals(other.typeid))
return false;
return true;
}
}