精通HIBERNATE---------读书笔记第十章 映射组成关系

晶粒度对象模型：把类中多个属性抽象出一个类，方便代码重用

public class Customer3 implements java.io.Serializable{
	private Long id;
	private String name;
	private Address homeAddress;
	private Address comAddress;

 

public class Address implements java.io.Serializable{
	private final String province;
	private final String city;
	private final String street;
	private final String zipcode;

把Address抽象出来了，注意Address没有主键！！
get，set方法省略，

对于表，应尽量减少外键，而不是可以定义2个表Customer和address

如下

create table CUSTOMERS (ID bigint not null, NAME varchar(15), HOME_PROVINCE varchar(255), HOME_CITY varchar(255), HOME_STREET varchar(255), HOME_ZIPCODE varchar(255), COM_PROVINCE varchar(255), COM_CITY varchar(255), COM_STREET varchar(255), COM_ZIPCODE varchar(255), primary key (ID));

然后用component组件定义映射关系

hibernate-mapping>
	
		
			
		

 

name是属性名，class是对应的类，parent是Address所属的整体类，即Customer，并且在Address类里要有setCustomer,getCustomer,这个要特别注意！！

区分一下Value类型和Entity类型

比如Address就是value类型，他没有自己的主键，不能单独持久化，session.save(address)是会报错的，而entity类型是有主键的，并且可以单独持久化。

删除customer时，所以value类型都会删除，而entity类型，要看cascade是否支持级联删除。

应用组成关系的持久化类：

 public void saveCustomer(){
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      
      Customer customer=new Customer();
      Address homeAddress=new Address("province1","city1","street1","100001",customer);
      Address comAddress=new Address("province2","city2","street2","200002",customer);
      customer.setName("Tom");
      customer.setHomeAddress(homeAddress);
      customer.setComAddress(comAddress);

      session.save(customer);
     
      tx.commit();

    }catch (RuntimeException e) {
      if (tx != null) {
        tx.rollback();
      }
      throw e;
    } finally {
        session.close();
    }
  }

 

 public void printCustomerAddress(Customer customer){
    Address homeAddress=customer.getHomeAddress();
    Address comAddress=customer.getComAddress();
    if(homeAddress==null)
      System.out.println("Home Address of "+customer.getName()+" is null.");
    else
      System.out.println("Home Address of "+customer.getName()+" is: " 
      +homeAddress.getProvince()+" "
      +homeAddress.getCity()+" "
      +homeAddress.getStreet());

  if(comAddress==null)
      System.out.println("Company Address of "+customer.getName()+" is null.");
    else
      System.out.println("Company Address of "+customer.getName()+" is: "
      +comAddress.getProvince()+" "
      +comAddress.getCity()+" "
      +comAddress.getStreet());
  }

 public void deleteCustomer(Customer customer){
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();

      session.delete(customer);
      tx.commit();

    }catch (RuntimeException e) {
      if (tx != null) {
        tx.rollback();
      }
      throw e;
    } finally {
        session.close();
    }
  }

映射符合组成关系，就是组件套组件，组件里面还有多对一，看代码吧

还有一个主意的就是value类型是不能有映射文件的，比如这个例子中 graphicsCard和cpuBox都不能有hbm.xml而entity就要有了，如Vendor.hbm.xml

最后希望大家一同提高吧！