jpa onetomany

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; } }