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>();)

 1 package com.dx.hibernate.onetomany;
 2 
 3 import java.util.HashSet;
 4 import java.util.List;
 5 import java.util.Set;
 6 
 7 public class Customer {
 8     private Integer customerId;
 9     private String customerName;
10     private Set<Order> orders = new HashSet<Order>();
11 
12     public Customer() {
13     }
14 
15     public Customer(String customerName) {
16         super();
17         this.customerName = customerName;
18     }
19 
20     public Integer getCustomerId() {
21         return customerId;
22     }
23 
24     public void setCustomerId(Integer customerId) {
25         this.customerId = customerId;
26     }
27 
28     public String getCustomerName() {
29         return customerName;
30     }
31 
32     public void setCustomerName(String customerName) {
33         this.customerName = customerName;
34     }
35 
36     public Set<Order> getOrders() {
37         return orders;
38     }
39 
40     public void setOrders(Set<Order> orders) {
41         this.orders = orders;
42     }
43 }
View Code

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>

 

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2017-6-1 15:27:44 by Hibernate Tools 3.5.0.Final -->
 5 <hibernate-mapping>
 6     <class name="com.dx.hibernate.onetomany.Customer" table="CUSTOMER">
 7         <id name="customerId" type="java.lang.Integer">
 8             <column name="CUSTOMER_ID" />
 9             <generator class="native" />
10         </id>
11         <property name="customerName" type="java.lang.String">
12             <column name="CUSTOMER_NAME" />
13         </property>
14         <set name="orders" table="ORDERS" inverse="false" lazy="true">
15             <key>
16                 <column name="CUSTOMER_ID" />
17             </key>
18             <one-to-many class="com.dx.hibernate.onetomany.Order" />
19         </set>
20     </class>
21 </hibernate-mapping>
View Code

Order.java

 1 package com.dx.hibernate.onetomany;
 2 
 3 public class Order {
 4     private Integer orderId;
 5     private String orderName;
 6     private Customer customer;
 7 
 8     public Order() {
 9         super();
10     }
11 
12     public Order(String orderName) {
13         super();
14         this.orderName = orderName;
15     }
16 
17     public Integer getOrderId() {
18         return orderId;
19     }
20 
21     public void setOrderId(Integer orderId) {
22         this.orderId = orderId;
23     }
24 
25     public String getOrderName() {
26         return orderName;
27     }
28 
29     public void setOrderName(String orderName) {
30         this.orderName = orderName;
31     }
32 
33     public Customer getCustomer() {
34         return customer;
35     }
36 
37     public void setCustomer(Customer customer) {
38         this.customer = customer;
39     }
40 
41 }
View Code

Order.hbm.xml

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2017-6-1 15:27:44 by Hibernate Tools 3.5.0.Final -->
 5 <hibernate-mapping>
 6     <class name="com.dx.hibernate.onetomany.Order" table="ORDERS">
 7         <id name="orderId" type="java.lang.Integer">
 8             <column name="ORDER_ID" />
 9             <generator class="native" />
10         </id>
11         <property name="orderName" type="java.lang.String">
12             <column name="ORDER_NAME" />
13         </property>
14         <many-to-one name="customer" class="com.dx.hibernate.onetomany.Customer" fetch="join">
15             <column name="CUSTOMER_ID" />
16         </many-to-one>
17     </class>
18 </hibernate-mapping>
View Code

测试1：

 1 @Test
 2     public void test() {
 3         Order order1 = new Order("order1");
 4         Order order2 = new Order("order2");
 5         Customer customer = new Customer("customer1");
 6         
 7         // 当Customer.hbm.xml中set节点属性Inverse为false时。
 8         customer.getOrders().add(order1);
 9         customer.getOrders().add(order2);
10 
11         session.save(customer);
12         session.save(order1);
13         session.save(order2);
14 
15         Customer customerFetch = (Customer) session.get(Customer.class, 1);
16 
17         System.out.println(customerFetch.getCustomerName());
18         System.out.println(customerFetch.getOrders().size());
19         System.out.println(customerFetch.getOrders().getClass());
20 
21     }
View Code

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"

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2017-6-1 15:27:44 by Hibernate Tools 3.5.0.Final -->
 5 <hibernate-mapping>
 6     <class name="com.dx.hibernate.onetomany.Customer" table="CUSTOMER">
 7         <id name="customerId" type="java.lang.Integer">
 8             <column name="CUSTOMER_ID" />
 9             <generator class="native" />
10         </id>
11         <property name="customerName" type="java.lang.String">
12             <column name="CUSTOMER_NAME" />
13         </property>
14         <set name="orders" table="ORDERS" inverse="true" lazy="true">
15             <key>
16                 <column name="CUSTOMER_ID" />
17             </key>
18             <one-to-many class="com.dx.hibernate.onetomany.Order" />
19         </set>
20     </class>
21 </hibernate-mapping>
View Code

测试代码：

 1     @Test
 2     public void test() {
 3         Order order1 = new Order("order1");
 4         Order order2 = new Order("order2");
 5         Customer customer = new Customer("customer1");
 6         
 7         // 当Customer.hbm.xml中set节点属性inverse为false时。
 8         // customer.getOrders().add(order1);
 9         // customer.getOrders().add(order2);
10 
11         // 当Customer.hbm.xml中set节点属性inverse为true时。
12         order1.setCustomer(customer);
13         order2.setCustomer(customer);
14 
15         session.save(customer);
16         session.save(order1);
17         session.save(order2);
18 
19         Customer customerFetch = (Customer) session.get(Customer.class, 1);
20 
21         System.out.println(customerFetch.getCustomerName());
22         System.out.println(customerFetch.getOrders().size());
23         System.out.println(customerFetch.getOrders().getClass());
24 
25     }
View Code

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

1         <set name="orders" table="ORDERS" inverse="true" lazy="true" cascade="save-update,delete" order-by="CUSTOMER_ID desc">
2             <key>
3                 <column name="CUSTOMER_ID" />
4             </key>
5             <one-to-many class="com.dx.hibernate.onetomany.Order" />
6         </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。

 

posted @ 2017-06-01 15:40  cctext  阅读(1297)  评论(0)  编辑  收藏  举报