在Hibernate中,component是某个实体的逻辑组成部分&＃xff0c;它与实体的根本区别是没有oid&＃xff08;对象标识符&＃xff09;&＃xff0c;component是一个被包含的对象,它作为值类型被持久化&＃xff0c;而非一个实体&＃xff08;摘自网络&＃xff09;
例如网上最常举的例子&＃xff1a;类User&＃xff0c;Address。一个Address应该是一个User的一部分&＃xff0c;在映射中&＃xff0c;当然可以把地址单独映射成一张表&＃xff0c;与User一对一映射&＃xff1b;但是这里最可取的方式&＃xff0c;是将Address以组件的方式映射到User中。
类User:
1 public class User {
2
3 private Integer id;
4 private String name;
5 private int age;
6 private Date birth;
7 private Address address;
8
9 // getters...
10 // setters...
11
12 }
类Address:
1 public class Address {
2
3 private String province;
4 private String city;
5 private String county;
6
7 // setters...
8
9 // getters...
10 }
映射文件User.hbm.xml&＃xff1a;
1 xml version&＃61;"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
5 <hibernate-mapping package&＃61;"com.zit.hibernateTest.entities">
6 <class name&＃61;"User" table&＃61;"USER_5">
7 <id name&＃61;"id" type&＃61;"java.lang.Integer">
8 <column name&＃61;"ID" />
9 <generator class&＃61;"increment" />
10 id>
11 <property name&＃61;"name" type&＃61;"java.lang.String">
12 <column name&＃61;"NAME" />
13 property>
14 <property name&＃61;"age" type&＃61;"int">
15 <column name&＃61;"AGE" />
16 property>
17 <property name&＃61;"birth" type&＃61;"java.util.Date">
18 <column name&＃61;"BIRTH" />
19 property>
20
21 <component name&＃61;"address" class&＃61;"Address">
22 <property name&＃61;"province" column&＃61;"address_province">property>
23 <property name&＃61;"city" column&＃61;"address_city">property>
24 <property name&＃61;"county" column&＃61;"address_county">property>
25 <property name&＃61;"street" column&＃61;"address_street">property>
26
27 component>
28 class>
29 hibernate-mapping>
User.hbm.xml中&＃xff0c;以component子元素将组件Address包含进来&＃xff0c;在生成表时&＃xff0c;会将Address的属性&＃xff0c;映射成User表的字段&＃xff0c;与User表中的其他字段平行。
数据库&＃xff1a;
PS:
组件映射&＃xff0c;Address不生成oid&＃xff0c;是值类型&＃xff0c;是值类型还是实体类型&＃xff0c;并没有非常明显的界线。
将Address以一对一的映射方式映射&＃xff08;主键的映射方式、外键的映射方式&＃xff09;&＃xff0c;也是可以的。
京公网安备 11010802041100号