JPA 一对多实例配置
<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0"> <persistence-unit name="mengya" transaction-type="RESOURCE_LOCAL"> <properties> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/> <property name="hibernate.hbm2ddl.auto" value="update"/> <property name="hibernate.connection.driver_class" value="org.gjt.mm.mysql.Driver"/> <property name="hibernate.connection.username" value="root"/> <property name="hibernate.connection.password" value="123"/> <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/mp?useUnicode=true&characterEncoding=UTF-8"/> </properties> </persistence-unit></persistence>
?在JPA中双向一对多关系则多方为关系护端即负责外键记录的更新，一方为被维护端即没有权力更新外键记录
src下在面的META-INF/persistence.xml配置如下：
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订单和订单项两个实例实体Bean如下：
订单表：
package com.mengya.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 orderId;private Float amount = 0f;// 设置默认值private Set<OrderItem> items = new HashSet<OrderItem>();@Id@Column(length = 32)public String getOrderId() {return orderId;}public void setOrderId(String orderId) {this.orderId = orderId;}@Column(nullable = false)public Float getAmount() {return amount;}public void setAmount(Float amount) {this.amount = amount;}// cascade表示级联操作// CascadeType.MERGE级联更新：若items属性修改了那么order对象保存时同时修改items里的对象。对应EntityManager的merge方法// CascadeType.PERSIST级联刷新：获取order对象里也同时也重新获取最新的items时的对象。对应EntityManager的refresh(object)方法有效。即会重新查询数据库里的最新数据// CascadeType.REFRESH级联保存：对order对象保存时也对items里的对象也会保存。对应EntityManager的presist方法// CascadeType.REMOVE级联删除：对order对象删除也对items里的对象也会删除。对应EntityManager的remove方法// FetchType.LAZY表示懒加载。对于xxxtoMany时即获得多的一方fetch的默认值是FetchType.LAZY懒加载。对于xxxtoOne时即获得一的一方fetch的默认值是FetchType.EAGER立即加载// mappedBy表示关系统被维护端，它的值是关系维护端维护关系的属性@OneToMany(cascade = { CascadeType.PERSIST, CascadeType.REFRESH,CascadeType.REMOVE }, fetch = FetchType.LAZY, mappedBy = "order")public Set<OrderItem> getItems() {return items;}public void setItems(Set<OrderItem> items) {this.items = items;}/** * 自己的加的一个方法，为了方便添加OrderItem * */public void addOrderItem(OrderItem item) {item.setOrder(this);this.items.add(item);}}?订单项表：
package com.mengya.bean;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;@Entitypublic class OrderItem {private Integer id;private String productName;private Float sellPrice = 0f;// 设置默认值private Order order;@Id@GeneratedValue(strategy = GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}@Column(length = 40, 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;}// cascade表示级联。CascadeType.REFRESH级联刷新// optional表示该对象可有可无，它的值为true表示该外键可以为null，它的值为false表示该外键为not null@ManyToOne(cascade = CascadeType.REFRESH, fetch = FetchType.EAGER, optional = false)// JoinColumn表示外键的列@JoinColumn(name="orderId")public Order getOrder() {return order;}public void setOrder(Order order) {this.order = order;}}?
测试：
package com.mengya.junit.test;import javax.persistence.EntityManager;import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence;import org.junit.Test;import com.mengya.bean.Order;import com.mengya.bean.OrderItem;public class JPA_OnetoManyTest {@Test public void save(){EntityManagerFactory factory=Persistence.createEntityManagerFactory("mengya");EntityManager em=factory.createEntityManager();em.getTransaction().begin();Order order=new Order();order.setOrderId("200910120001");order.setAmount(450f);OrderItem item1=new OrderItem();item1.setProductName("篮球");item1.setSellPrice(220f);OrderItem item2=new OrderItem();item2.setProductName("排球");item2.setSellPrice(230f);order.addOrderItem(item1);order.addOrderItem(item2);em.persist(order);em.getTransaction().commit();em.close();factory.close();}}?
1 楼 daquan198163 2009-10-13 红字部分我看不懂