hibernate一对多

订单和订单项就是一对多的关系。一个订单有多个订单项，一个订单项属于某个订单。

订单和订单项映射后的表结构如下：

订单表结构

订单项表结构

下面就以订单和订单项为例介绍多对多映射关系的实例开发

persistence.xml配置文件

 

<?xml version="1.0"?><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">  <!--事务类型：本地事务(仅针对一个数据库)和全局事务(针对多个数据库)；RESOURCE_LOCAL: 本地事务 -->  <persistence-unit name="ljq" transaction-type="RESOURCE_LOCAL">      <properties>         <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>         <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="mysql"/>         <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/test?useUnicode=true&amp;characterEncoding=UTF-8"/>         <property name="hibernate.hbm2ddl.auto" value="update"/>      </properties>  </persistence-unit></persistence>

Order订单类

 

package com.ljq.entity;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;/** * one端 *  * 碰到many为末端的加载就是延迟加载，若one为末端则为立即加载，除了one-to-one。 *  * @author jiqinlin *  */@Entity@Table(name = "tb_order")@SuppressWarnings("serial")public class Order implements java.io.Serializable {    // String类型不能用uuid，需要人为指定    @Id    @Column(length = 12)    private String orderid;    @Column(nullable = false)    private Float amount = 0f;    // @OneToMany(cascade={CascadeType.PERSIST,CascadeType.MERGE,CascadeType.REMOVE})    // mappedBy="order": 指明Order类为双向关系维护端，负责外键的更新    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "order")    private Set<OrderItem> items = new HashSet<OrderItem>();    public Order() {        super();    }    public Float getAmount() {        return amount;    }    public void setAmount(Float amount) {        this.amount = amount;    }    public String getOrderid() {        return orderid;    }    public void setOrderid(String orderid) {        this.orderid = orderid;    }    public Set<OrderItem> getItems() {        return items;    }    public void setItems(Set<OrderItem> items) {        this.items = items;    }    ////////////////////////////////////    /**     * 添加订单项     *      * @param student     */    public void addOrderItem(OrderItem item) {        if (!this.items.contains(item)) {            this.items.add(item);            item.setOrder(this);        }    }    /**     * 删除订单项     *      * @param student     */    public void removeOrderItem(OrderItem item) {        if (this.items.contains(item)) {            item.setOrder(null);            this.items.remove(item);        }    }}

OrderItem订单项类

 

package com.ljq.entity;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;/** * many端 *  * 在one-to-many双向关联中，多的一方为关系维护端，关系维护端负责外键记录的更新  * 关系被维护端是没有权力更新外键记录的 *  * @author jiqinlin *  */@Entity@Table(name = "tb_orderitem")@SuppressWarnings("serial")public class OrderItem implements java.io.Serializable {    @Id    @GeneratedValue    private Integer id;    @Column(length = 40, nullable = false)    private String productName;    @Column(nullable = false)    private Float sellPrice = 0f;    // optional=true：可选，表示此对象可以没有，可以为null；false表示必须存在    @ManyToOne(cascade = { CascadeType.REFRESH, CascadeType.MERGE }, optional = true)    @JoinColumn(name = "order_id")    private Order order;    public OrderItem() {        super();    }    public OrderItem(String productName, Float sellPrice) {        super();        this.productName = productName;        this.sellPrice = sellPrice;    }    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getProductName() {        return productName;    }    public void setProductName(String productName) {        this.productName = productName;    }    public Float getSellPrice() {        return sellPrice;    }    public void setSellPrice(Float sellPrice) {        this.sellPrice = sellPrice;    }    public Order getOrder() {        return order;    }    public void setOrder(Order order) {        this.order = order;    }}

OrderTest测试类

 

package com.ljq.test;import java.io.Serializable;import java.util.List;import java.util.Set;import java.util.UUID;import javax.persistence.EntityManager;import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence;import org.junit.Test;import com.ljq.entity.Order;import com.ljq.entity.OrderItem;import com.sun.org.apache.xpath.internal.operations.Or;public class OrderTest {    /**     * 添加订单Order时同时添加两个订单项OrderItem，因为订单Order为双向关系维护者，起着主导作用     */    @Test    public void save() {        EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq");        EntityManager em = factory.createEntityManager();        em.getTransaction().begin();        Order order = new Order();        order.setAmount(34f);        //UUID.randomUUID().toString()        order.setOrderid("xxxx");         order.addOrderItem(new OrderItem("足球",20f));        order.addOrderItem(new OrderItem("篮球",25f));        em.persist(order);        em.getTransaction().commit();        em.close();        factory.close();    }        /**     * 删除Order对象时，会自动删除OrderItem对象（即：父对象删除时子对象跟着删除）     */    @Test    public void detele1(){        EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq");        EntityManager em = factory.createEntityManager();        em.getTransaction().begin();                Order order=em.getReference(Order.class, "xxxx");        em.remove(order);                em.getTransaction().commit();        em.close();        factory.close();    }        /**     * 删除子对象时，父对象没影响     */    @Test    public void detele2(){        EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq");        EntityManager em = factory.createEntityManager();        em.getTransaction().begin();                OrderItem item=em.getReference(OrderItem.class, (Serializable)3);        em.remove(item);                em.getTransaction().commit();        em.close();        factory.close();        }    //运行结果为：    //orderid:xxxx, amount:34.0    //productName:足球price:20.0    //productName:篮球price:25.0    //===============    @Test    public void find1(){        EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq");        EntityManager em = factory.createEntityManager();        em.getTransaction().begin();                List<Order> orders=em.createQuery("select o from Order o").getResultList();        for(Order order:orders){            System.out.println("orderid:"+order.getOrderid()+", "+"amount:"+order.getAmount());            Set<OrderItem> orderItems=order.getItems();            for(OrderItem item:orderItems){                System.out.println("productName:"+item.getProductName()+"price:"+item.getSellPrice());            }            System.out.println("===============");        }        em.close();        factory.close();    }        //运行结果为    //productName:足球price:20.0    //orderid:xxxx, amount:34.0    //============    //productName:篮球price:25.0    //orderid:xxxx, amount:34.0    //============    @Test    public void find2(){        EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq");        EntityManager em = factory.createEntityManager();        em.getTransaction().begin();                List<OrderItem> items=em.createQuery("select o from OrderItem o").getResultList();        for(OrderItem item:items){            System.out.println("productName:"+item.getProductName()+"price:"+item.getSellPrice());            Order order=item.getOrder();            System.out.println("orderid:"+order.getOrderid()+", "+"amount:"+order.getAmount());            System.out.println("============");        }        em.close();        factory.close();    }            /**     * 测试jpa环境是否搭建成功     *      */    @Test    public void test() {        Persistence.createEntityManagerFactory("ljq");    }}