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><class name="com.yuxuan.Customer3" table="CUSTOMERS3"><id name="id" type="long" column="ID"><generator class="increment"></generator></id>

 

<component name="homeAddress" class="com.yuxuan.Address"><parent name="customer3"></parent> <property name="province" type="string" column="HOME_PROVINCE"/>            <property name="city" type="string" column="HOME_CITY"/>            <property name="street" type="string" column="HOME_STREET"/>            <property name="zipcode" type="string" column="HOME_ZIPCODE"/></component>

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

<hibernate-mapping >  <class name="mypack.Computer" table="COMPUTERS" >    <id name="id" type="long" column="ID">      <generator class="increment"/>    </id>    <property name="type" type="string" >        <column name="COMPUTER_TYPE" length="15" />    </property>        <component name="cpuBox" class="mypack.CpuBox">            <parent name="computer" />                        <property name="type" type="string" >                <column name="CPUBOX_TYPE" length="15" />            </property>                        <component name="graphicsCard" class="mypack.GraphicsCard">               <parent name="cpuBox" />                             <property name="type" type="string" >                  <column name="GRAPHICSCARD_TYPE" length="15" />               </property>            </component>            <many-to-one        name="vendor"        column="CPUBOX_VENDOR_ID"        class="mypack.Vendor"        not-null="true"             />    </component>  </class> </hibernate-mapping>

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！