Hibernate 映射组成关系-优快云博客

本文介绍了一种通过ORM将数据库表结构映射到Java对象的方法，特别关注于如何将地址信息抽象为独立的Address类，以提高代码的可重用性和维护性。

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SQL：

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));

Customer类中可把地址信息抽象出单独的Address类，来提高程序代码的可重用性。

Customer.java：

package mypack;
public class Customer  implements java.io.Serializable {
    private long id;
    private String name;
    private Address homeAddress;
    private Address comAddress;

    constructor()...; getter()...; setter()...;

}

Address.java：

package mypack;
public class Address  implements java.io.Serializable {
    private String province;
    private String city;
    private String street;
    private String zipcode;
    private Customer customer;

    constructor()...; getter()...; setter()...;

}

Customer.hbm.xml：

<class name="mypack.Customer" table="CUSTOMERS">

    <id name="id" type="long" column="ID">

        <generator class="increment" />

    </id>

    <property name="name" type="string">

        <column name="NAME" length="15" />

    </property>

    <component name="homeAddress" class="mypack.Address">

        <parent name="customer" />

        <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>

    <component name="comAddress" class="mypack.Address">

        <parent name="customer" />

        <property name="province" type="string" column="COM_PROVINCE" />

        <property name="city" type="string" column="COM_CITY" />

        <property name="street" type="string" column="COM_STREET" />

        <property name="zipcode" type="string" column="COM_ZIPCODE" />

    </component>

</class>

此时，Address类属于值类型，没有OID，不能单独进行持久化。Customer属于实体类型，可单独持久化。

在<component>元素中还能嵌套<component>元素，用来映射复合组成关系。