Hibernate（七）：*.hbm.xml配置文件中Set三个属性

• 背景：

　　在上一篇文章中实现双向关联时，其中在Customer.java中我们使用了java.util.List<Order>来关联多的Order。其实还有另外一种实现方法：使用java.util.Set来替代java.util.List。

Customer.java(定义Order:private java.util.Set<Order> orders=new HashSet<Order>();)

 package com.dx.hibernate.onetomany;

 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;

 public class Customer {
     private Integer customerId;
     private String customerName;
     private Set<Order> orders = new HashSet<Order>();

     public Customer() {
     }

     public Customer(String customerName) {
         super();
         this.customerName = customerName;
     }

     public Integer getCustomerId() {
         return customerId;
     }

     public void setCustomerId(Integer customerId) {
         this.customerId = customerId;
     }

     public String getCustomerName() {
         return customerName;
     }

     public void setCustomerName(String customerName) {
         this.customerName = customerName;
     }

     public Set<Order> getOrders() {
         return orders;
     }

     public void setOrders(Set<Order> orders) {
         this.orders = orders;
     }
 }

Customer.hbm.xml

set 节点设置为：

        <set name="orders" table="ORDERS" inverse="true" lazy="true">
            <key>
                <column name="CUSTOMER_ID" />
            </key>
            <one-to-many class="com.dx.hibernate.onetomany.Order" />
        </set>

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <!-- Generated 2017-6-1 15:27:44 by Hibernate Tools 3.5.0.Final -->
 <hibernate-mapping>
     <class name="com.dx.hibernate.onetomany.Customer" table="CUSTOMER">
         <id name="customerId" type="java.lang.Integer">
             <column name="CUSTOMER_ID" />
             <generator class="native" />
         </id>
         <property name="customerName" type="java.lang.String">
             <column name="CUSTOMER_NAME" />
         </property>
         <set name="orders" table="ORDERS" inverse="false" lazy="true">
             <key>
                 <column name="CUSTOMER_ID" />
             </key>
             <one-to-many class="com.dx.hibernate.onetomany.Order" />
         </set>
     </class>
 </hibernate-mapping>

Order.java

 package com.dx.hibernate.onetomany;

 public class Order {
     private Integer orderId;
     private String orderName;
     private Customer customer;

     public Order() {
         super();
     }

     public Order(String orderName) {
         super();
         this.orderName = orderName;
     }

     public Integer getOrderId() {
         return orderId;
     }

     public void setOrderId(Integer orderId) {
         this.orderId = orderId;
     }

     public String getOrderName() {
         return orderName;
     }

     public void setOrderName(String orderName) {
         this.orderName = orderName;
     }

     public Customer getCustomer() {
         return customer;
     }

     public void setCustomer(Customer customer) {
         this.customer = customer;
     }

 }

Order.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <!-- Generated 2017-6-1 15:27:44 by Hibernate Tools 3.5.0.Final -->
 <hibernate-mapping>
     <class name="com.dx.hibernate.onetomany.Order" table="ORDERS">
         <id name="orderId" type="java.lang.Integer">
             <column name="ORDER_ID" />
             <generator class="native" />
         </id>
         <property name="orderName" type="java.lang.String">
             <column name="ORDER_NAME" />
         </property>
         <many-to-one name="customer" class="com.dx.hibernate.onetomany.Customer" fetch="join">
             <column name="CUSTOMER_ID" />
         </many-to-one>
     </class>
 </hibernate-mapping>

测试1：

 @Test
     public void test() {
         Order order1 = new Order("order1");
         Order order2 = new Order("order2");
         Customer customer = new Customer("customer1");

         // 当Customer.hbm.xml中set节点属性Inverse为false时。
         customer.getOrders().add(order1);
         customer.getOrders().add(order2);

         session.save(customer);
         session.save(order1);
         session.save(order2);

         Customer customerFetch = (Customer) session.get(Customer.class, 1);

         System.out.println(customerFetch.getCustomerName());
         System.out.println(customerFetch.getOrders().size());
         System.out.println(customerFetch.getOrders().getClass());

     }

测试通过。

在运行过程中Customer.java中Set为：class org.hibernate.collection.internal.PersistentSet，属于hibernate的一个代理对象。

session关闭，将抛出异常。

测试2：

修改Customer.hbm.xml中set节点属性inverse="true"

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <!-- Generated 2017-6-1 15:27:44 by Hibernate Tools 3.5.0.Final -->
 <hibernate-mapping>
     <class name="com.dx.hibernate.onetomany.Customer" table="CUSTOMER">
         <id name="customerId" type="java.lang.Integer">
             <column name="CUSTOMER_ID" />
             <generator class="native" />
         </id>
         <property name="customerName" type="java.lang.String">
             <column name="CUSTOMER_NAME" />
         </property>
         <set name="orders" table="ORDERS" inverse="true" lazy="true">
             <key>
                 <column name="CUSTOMER_ID" />
             </key>
             <one-to-many class="com.dx.hibernate.onetomany.Order" />
         </set>
     </class>
 </hibernate-mapping>

测试代码：

     @Test
     public void test() {
         Order order1 = new Order("order1");
         Order order2 = new Order("order2");
         Customer customer = new Customer("customer1");

         // 当Customer.hbm.xml中set节点属性inverse为false时。
         // customer.getOrders().add(order1);
         // customer.getOrders().add(order2);

         // 当Customer.hbm.xml中set节点属性inverse为true时。
         order1.setCustomer(customer);
         order2.setCustomer(customer);

         session.save(customer);
         session.save(order1);
         session.save(order2);

         Customer customerFetch = (Customer) session.get(Customer.class, 1);

         System.out.println(customerFetch.getCustomerName());
         System.out.println(customerFetch.getOrders().size());
         System.out.println(customerFetch.getOrders().getClass());

     }

测试通过。

接下来我们要将的是set节点的三个重要属性：inverse,cascade,order-by。

• inverse属性

1）在Hibernate中通过对inverse属性来决定是有双向关联的哪一方来维护表和表之间的关系。inverse=false为主动方，inverse=true的为被动方，由主动方负责维护关联关系。

2）在没有设置inverse=true的情况下，父子两边都维护父子关系。

3）在1-n关系中，将n方设为主控方将有助于性能改善。

• cascade属性

级联，每个Hibernate session的基本操作包括persist()、merge()、saveOrUpdate(）、delete()、lock()、refresh()、evict()、replicate()，这些操作都有对应的级联风格（cascade style）。这些级联风格（cascade style）风格分别命名为persist、merge、save-update、delete、lock、refresh、evict、replicate。

级联风格	Session中的方法
persist	persist()
merge	merge()
save-update	save()、update()、saveOrUpdate()
delete	delete()
lock	lock()
refresh	refresh()
evict	evict()
replicate	replicate()

注意：

一般默认是不建议设置cascade属性。

• order-by属性

设置查询时，排序方式。

测试1:

修改Customer.hbml.xml

         <set name="orders" table="ORDERS" inverse="true" lazy="true" cascade="save-update,delete" order-by="CUSTOMER_ID desc">
             <key>
                 <column name="CUSTOMER_ID" />
             </key>
             <one-to-many class="com.dx.hibernate.onetomany.Order" />
         </set>

修改test代码：

    @Test
    public void test() {
        Order order1 = new Order("order1");
        Order order2 = new Order("order2");
        Customer customer = new Customer("customer3");

        customer.getOrders().add(order1);
        customer.getOrders().add(order2);
        order1.setCustomer(customer);
        order2.setCustomer(customer);

        session.save(customer);
        // session.save(order1);
        // session.save(order2);
    }

    @Test
    public void testRemoveCustomer() {
        Customer customer = (Customer) session.get(Customer.class, 3);
        session.remove(customer);
    }

测试通过。