Posted on 2009-06-20 19:08
胡娟 阅读(2446)
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JAVA
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;
}
}