JPA OneToMany映射

二话不说上代码：

package com.jvwl.model;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.Id;import javax.persistence.OneToMany;import javax.persistence.Table;/** * 订单实体 * @author Jerval * */@Entity@Table(name="t_order")public class Order {private String orderId;private Float amount=0f;private Set<OrderItem> items = new HashSet<OrderItem>();@Id @Column(length=40)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;}@OneToMany(cascade={CascadeType.ALL},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);items.add(orderItem);}}

?

package com.jvwl.model;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;import javax.persistence.Table;/** * 订单项实体 * @author Jerval * */@Entity@Table(name="t_orderItem")public class OrderItem {private Integer id;private String productName;private Float sellPrice = 0f;private Order order;@Id@GeneratedValuepublic 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;}@ManyToOne(cascade = { CascadeType.REFRESH, CascadeType.MERGE }, optional = false)@JoinColumn(name = "order_id")public Order getOrder() {return order;}public void setOrder(Order order) {this.order = order;}}

?最后来个测试：

package junit.test;import java.util.List;import java.util.UUID;import javax.persistence.EntityManager;import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence;import org.junit.Test;import com.jvwl.model.Order;import com.jvwl.model.OrderItem;public class JPATest {@Testpublic void test() {EntityManagerFactory factory = Persistence.createEntityManagerFactory("jvwl");EntityManager em = factory.createEntityManager();em.getTransaction().begin();Order order = new Order();order.setAmount(108f);order.setOrderId(UUID.randomUUID().toString());OrderItem orderItem1 = new OrderItem();orderItem1.setOrder(order);orderItem1.setProductName("kk");orderItem1.setSellPrice(24f);order.addOrderItem(orderItem1);OrderItem orderItem2 = new OrderItem();orderItem2.setOrder(order);orderItem2.setProductName("ooo");orderItem2.setSellPrice(222f);order.addOrderItem(orderItem2);em.persist(order);em.getTransaction().commit();em.close();factory.close();}@SuppressWarnings("unchecked")@Testpublic void testQuery() {EntityManagerFactory factory = Persistence.createEntityManagerFactory("jvwl");EntityManager em = factory.createEntityManager();em.getTransaction().begin();List<Order> list = em.createQuery("select o from Order o").getResultList();for (Order o : list) {System.out.println(o.getOrderId());System.out.println(o.getItems().size());}em.getTransaction().commit();em.close();factory.close();}}

?