JPA+Hibernate 3.3 学习小结——双向多对一关联及级联操作

关系映射

package  com.hujuan.bean;

import  java.util.HashSet;
import  java.util.Set;

import  javax.persistence.CascadeType;
import  javax.persistence.Column;
import  javax.persistence.Entity;
import  javax.persistence.FetchType;
import  javax.persistence.Id;
import  javax.persistence.OneToMany;
import  javax.persistence.Table;

@Entity
@Table(name = " orders " )
public   class  Order {
    
     private  String id;
     private  Float amount;
     private  Set < OrderItem >  items  =   new  HashSet < OrderItem > ();
    
    @Id @Column(length = 10 )
     public  String getId() {
         return  id;
    }
     public   void  setId(String id) {
         this .id  =  id;
    }
    @Column(nullable = false )
     public  Float getAmount() {
         return  amount;
    }
     public   void  setAmount(Float amount) {
         this .amount  =  amount;
    }
     // 级联操作
    @OneToMany(cascade =  {CascadeType.REFRESH,CascadeType.PERSIST,CascadeType.MERGE,CascadeType.REMOVE},fetch = FetchType.LAZY,mappedBy = " order " )
     public  Set < OrderItem >  getItems() {
         return  items;
    }
     public   void  setItems(Set < OrderItem >  items) {
         this .items  =  items;
    }
    
     public   void  addOrderItem(OrderItem orderItem){
        orderItem.setOrder( this );
         this .items.add(orderItem);
    }
}

Cascade 级联操作
CascadeType. PERSIST 级联持久化 ( 保存 ) 操作
CascadeType. MERGE 级联更新 ( 合并 ) 操作
CascadeType. REFRESH 级联刷新操作，只会查询获取操作
CascadeType. REMOVE 级联删除操作
CascadeType. ALL 级联以上全部操作
Fetch 抓取是否延迟加载，默认情况一的方为立即加载，多的一方为延迟加载
mappedBy 关系维护
mappedBy= "order" 表示在 OrderItem 类中的 order 属性来维护关系

package  com.hujuan.bean;

import  javax.persistence.CascadeType;
import  javax.persistence.Column;
import  javax.persistence.Entity;
import  javax.persistence.GeneratedValue;
import  javax.persistence.Id;
import  javax.persistence.JoinColumn;
import  javax.persistence.ManyToOne;

@Entity
public   class  OrderItem {
    
     private  Integer id;
     private  String productName;
     private  Float sellPrice  =  0f;
     private  Order order;
    
    
    @Id @GeneratedValue
     public  Integer getId() {
         return  id;
    }
     public   void  setId(Integer id) {
         this .id  =  id;
    }
    @Column(length = 30 ,nullable = false )
     public  String getProductName() {
         return  productName;
    }
     public   void  setProductName(String productName) {
         this .productName  =  productName;
    }
    @Column(nullable = false )
     public  Float getSellPrice() {
         return  sellPrice;
    }
     public   void  setSellPrice(Float sellPrice) {
         this .sellPrice  =  sellPrice;
    }
     // optional=true表示该对象(Order)是可选的，对象(Order)可以不存在
     // 值为false表示不可选即该对象(Order)必须存在，则在数据库中的外键就不能为null）
    @ManyToOne(cascade = {CascadeType.MERGE,CascadeType.REFRESH},optional = false )
     // 定义外键名称
    @JoinColumn(name = " order_id " )
     public  Order getOrder() {
         return  order;
    }
     public   void  setOrder(Order order) {
         this .order  =  order;
    }
}