hibernate之一对多关系

1. 什么是关联(association)
1.1 关联指的是类之间的引用关系。如果类A与类B关联，那么被引用的类B将被定义为类A的属性。例如:
public class A{
private B b = new B;
public A(){}
}
1.2 关联的分类：关联可以分为一对一、一对多/多对一、多对多关联
关联是有方向的

现在我们就讲的是一对多

把实体及配置文件导入

Order

/**
 * hibernate关联关系
 * 一对多：一个订单对应多个订单项
 * 多对一：多个订单项对应一个订单（注：一个订单项对应一个订单）
 * @author Administrator
 *
 */
public class Order implements Serializable {
    //订单id
    private Integer orderId;
    //订单编号
    private String orderNO;

    //1.1 关联指的是类之间的引用关系。如果Order与类OrderItem关联，
    //那么被引用的OrderItem将被定义为Order 的属性。例如:
    private Set<OrderItem> orderitems=new HashSet<OrderItem>();

    public Set<OrderItem> getOrderitems() {
        return orderitems;
    }
    public void setOrderitems(Set<OrderItem> orderitems) {
        this.orderitems = orderitems;
    }
    public Integer getOrderId() {
        return orderId;
    }
    public void setOrderId(Integer orderId) {
        this.orderId = orderId;
    }
    public String getOrderNO() {
        return orderNO;
    }
    public void setOrderNO(String orderNO) {
        this.orderNO = orderNO;
    }
    public Order() {
        super();
    }
    @Override
    public String toString() {
        return "Order [orderId=" + orderId + ", orderNO=" + orderNO + ", orderitems=" + orderitems + "]";
    }

}

Order.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
   <class name="com.hmc.hibernate02.entity.Order" table="t_order_hb">
    <id name="orderId" type="java.lang.Integer" column="order_id">
    <!--native:identity(标识列)+sequence(序列)  -->
    <generator class="native"></generator>
    </id>
    <property name="orderNO" type="java.lang.String" column="order_no"/>
   <!--一方中的主键就是多方中的外键  -->
   <!--
   select o.*,oi.* from t_order_hb o inner join t_order_item_hb oi
   on o.order_id=oi.oid
    -->

   <!--建立关联关系  -->
   <!--
   name:实体类中定义的属性名，指向多方
   cassade:用来控制如何操作关联的持久化对象的

     -->
   <set name="orderitems" cascade="save-update" inverse="true" table="t_order_item_hb"  >
   <!-- 指定连接的多方中的外键列 -->
    <key column="oid"></key>
    <!--指定实体之间的关联关系：一对多  -->
    <!--class:指向的是多方的实体类的全路径名  -->
    <one-to-many class="com.hmc.hibernate02.entity.OrderItem"/>
   </set>
   </class> 

</hibernate-mapping>

OrderItem

/**
 *  多个订单项对应一个订单（注意：一个订单项唯一对应一个订单）
 * @author Administrator
 *
 */
public class OrderItem  implements Serializable{
    //订单项id
    private Integer orderItemId;
    //产品id
    private Integer productId;
    //数量
    private Integer quantity;
    //外键列
    private Integer oid;

    //1.1 关联指的是类之间的引用关系。如果OrderItem与类Order关联，
    //那么被引用的Order将被定义为OrderItem 的属性。例如:
    private Order order;

    public Order getOrder() {
        return order;
    }
    public void setOrder(Order order) {
        this.order = order;
    }
    public Integer getOrderItemId() {
        return orderItemId;
    }
    public void setOrderItemId(Integer orderItemId) {
        this.orderItemId = orderItemId;
    }
    public Integer getProductId() {
        return productId;
    }
    public void setProductId(Integer productId) {
        this.productId = productId;
    }
    public Integer getQuantity() {
        return quantity;
    }
    public void setQuantity(Integer quantity) {
        this.quantity = quantity;
    }
    public Integer getOid() {
        return oid;
    }
    public void setOid(Integer oid) {
        this.oid = oid;
    }
    @Override
    public String toString() {
        return "OrderItem [orderItemId=" + orderItemId + ", productId=" + productId + ", quantity=" + quantity
                + ", oid=" + oid + "]";
    }

OrderItem.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
   <class name="com.hmc.hibernate02.entity.OrderItem" table="t_order_item_hb">
    <id name="orderItemId" type="java.lang.Integer" column="order_item_id">
    <!--native:identity(标识列)+sequence(序列)  -->
    <generator class="native"></generator>
    </id>
    <property name="productId" type="java.lang.Integer" column="product_id"/>
    <property name="quantity" type="java.lang.Integer" column="quantity"/>
    <property insert="false" update="false" name="oid" type="java.lang.Integer" column="oid"/>
  <!--建立关联关系  -->
 <!--   name:实体类中定义的属性名，指向一方 -->
  <many-to-one name="order" cascade="save-update" class="com.hmc.hibernate02.entity.Order">
  <!--多方的数据库表中的外键列，指向一方  -->
  <column name="oid"></column>
  </many-to-one>

   </class> 

</hibernate-mapping>

OrderDao

 public void add(Order order) {
         Session session = SessionFactoryUtils.openSession();
         Transaction transaction = session.beginTransaction();
         session.save(order);
         transaction.commit();
         SessionFactoryUtils.closeSession();
     }

     public Order get(Order order) {
         Session session = SessionFactoryUtils.openSession();
         Transaction transaction = session.beginTransaction();
          Order o = session.get(Order.class, order.getOrderId());
        //处理懒加载
            if(null!=o) {
                Hibernate.initialize(o.getOrderitems());
            }
         transaction.commit();
         SessionFactoryUtils.closeSession();
         return o;
     }

     public void update(Order order){

         Session session = SessionFactoryUtils.openSession();
         Transaction transaction = session.beginTransaction();
        //先查，再更新
         Order o = session.get(Order.class, order.getOrderId());
         if(null!=o) {
             //拿到多方
             Set<OrderItem> orderitems = o.getOrderitems();

             OrderItem orderItem=null;
             for (int i = 0; i <=2; i++) {
                 orderItem=new OrderItem();
                 orderItem.setProductId(i);
                 orderItem.setQuantity(i+2);

                 //建立关联关系
                 orderItem.setOrder(o);
                 o.getOrderitems().add(orderItem);
            }
         session.update(o);
         }
         transaction.commit();
         SessionFactoryUtils.closeSession();

     }

     //级联删除
     public void delete(Order order) {
         Session Session = SessionFactoryUtils.openSession();
          Transaction Transaction = Session.beginTransaction();
         //先查询，在删除
          Order o = Session.get(Order.class, order.getOrderId());
          if(null!=o) {

              /**
               * 解除关联关系：先删从表，再删主表
               * 1）禁用联级删除
               * 2）先删从表，再删主表
               * 3）手动代码维护
               */
              Set<OrderItem> orderitems = o.getOrderitems();
              for (OrderItem orderItem : orderitems) {
                Session.delete(orderItem);
            }
              Session.delete(o);
          }

          Transaction.commit();
          SessionFactoryUtils.closeSession();
     }
     

测试类进行测试OrderDaoTest

Hibernate:
    select
        order0_.order_id as order_id1_0_0_,
        order0_.order_no as order_no2_0_0_
    from
        t_order_hb order0_
    where
        order0_.order_id=?
Hibernate:
    select
        orderitems0_.oid as oid4_1_0_,
        orderitems0_.order_item_id as order_it1_1_0_,
        orderitems0_.order_item_id as order_it1_1_1_,
        orderitems0_.product_id as product_2_1_1_,
        orderitems0_.quantity as quantity3_1_1_,
        orderitems0_.oid as oid4_1_1_
    from
        t_order_item_hb orderitems0_
    where
        orderitems0_.oid=?
Hibernate:
    delete
    from
        t_order_item_hb
    where
        order_item_id=?
Hibernate:
    delete
    from
        t_order_item_hb
    where
        order_item_id=?
Hibernate:
    delete
    from
        t_order_item_hb
    where
        order_item_id=?
Hibernate:
    delete
    from
        t_order_hb
    where
        order_id=?