本文将介绍怎样使用 MyBatis 实现对象一对一映射，下面通过一个具体实例来进行介绍。
（1）我们先看看实例涉及的数据表，该实例共涉及了 user（用户表） 和 user_contact（用户联系方式表） 表。假设一个用户只能拥有一个联系方式，则有如下数据：
其中，user.user_id 等于 user_contact.user_id 字段。下面将查询用户联系方式，然后也将用户信息查询出来，只不过用户信息是作为联系方式中的成员变量出现。
（2）根据上面数据表创建 user 和 user_contact 表映射的 JavaBean 实体。代码如下：
a、ORMContact.java
package com.hxstrive.mybatis.orm.demo2;
public class ORMContact {
private Integer id;
private Integer userId;
private String usage;
private String number;
private ORMUser user;
// 忽略 getter 和 setter
@Override
public String toString() {
return "ORMContact{" +
"id=" + id +
", userId=" + userId +
", usage='" + usage + '\'' +
", number='" + number + '\'' +
", user=" + user +
'}';
}
}b、ORMUser.java
package com.hxstrive.mybatis.orm.demo2;
import java.util.Date;
import java.util.List;
public class ORMUser {
private Integer userId;
private String name;
private String sex;
private Integer age;
private Double salary;
private Date borthday;
private byte[] face;
// 忽略 getter 和 setter
@Override
public String toString() {
return "ORMUser{" +
"userId=" + userId +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
", age=" + age +
", salary=" + salary +
", borthday=" + borthday +
'}';
}
}（3）MyBatis 配置文件 mybatis-cfg.xml 文件代码如下：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="database.properties"/>
<environments default="MySqlDatabase" >
<environment id="MySqlDatabase" >
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/hxstrive/mybatis/orm/demo2/ORMMapper.xml"/>
</mappers>
</configuration>（4）定义 Mapper 接口文件 ORMMapper.java，文件内容如下：
package com.hxstrive.mybatis.orm.demo2;
import java.util.List;
public interface ORMMapper {
/**
* 查询所有的联系方式信息
*/
List<ORMContact> joinSelect02();
}（5）定义 Mapper XML 文件 ORMMapper.xml，文件内容如下：
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.hxstrive.mybatis.orm.demo2.ORMMapper"> <!-- 对象一对一的关联映射，ORMContact对象中有ORMUser对象 --> <resultMap id="ormContact" type="com.hxstrive.mybatis.orm.demo2.ORMContact"> <id column="id" jdbcType="INTEGER" property="id" /> <result column="user_id" jdbcType="INTEGER" property="userId" /> <result column="usage" jdbcType="VARCHAR" property="usage" /> <result column="number" jdbcType="VARCHAR" property="number" /> <!-- 关联映射 --> <association column="n_userid" property="user" javaType="com.hxstrive.mybatis.orm.demo2.ORMUser"> <id column="user_id" jdbcType="INTEGER" property="userId" /> <result column="name" jdbcType="VARCHAR" property="name" /> <result column="sex" jdbcType="VARCHAR" property="sex" /> <result column="age" jdbcType="INTEGER" property="age" /> <result column="salary" jdbcType="DOUBLE" property="salary" /> <result column="borthday" jdbcType="DATE" property="borthday" /> </association> </resultMap> <select id="joinSelect02" resultMap="ormContact"> select a.`user_id`, a.`name`, a.`sex`, a.`age`, a.`salary`, a.`borthday`, b.`id`, b.`user_id`, b.`usage`, b.`number` from `user` a join `user_contact` b on a.`user_id`=b.`user_id` </select> </mapper>
（6）客户端代码如下：
package com.hxstrive.mybatis.orm.demo2;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.InputStream;
import java.util.List;
public class OrmDemo {
public static void main(String[] args) throws Exception {
String cfgName = "com/hxstrive/mybatis/orm/demo2/mybatis-cfg.xml";
InputStream input = Resources.getResourceAsStream(cfgName);
SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlFactory = factoryBuilder.build(input);
SqlSession sqlSession = sqlFactory.openSession(true);
ORMMapper ormMapper = sqlSession.getMapper(ORMMapper.class);
List<ORMContact> contactList = ormMapper.joinSelect02();
for ( ORMContact contact : contactList ) {
System.out.println(contact);
}
}
}运行程序，输出如下结果：
ORMContact{id=1, userId=1, usage='手机号码', number='15787782291', user=ORMUser{userId=1, name='Helen', sex='男', age=28, salary=7800.0, borthday=Wed Jun 04 00:00:00 CST 1902}}
ORMContact{id=2, userId=2, usage='家庭号码', number='028-82234543', user=ORMUser{userId=2, name='张小凡', sex='男', age=30, salary=8670.0, borthday=Wed Aug 22 00:00:00 CDT 1990}}
ORMContact{id=3, userId=3, usage='工作号码', number='028-78675599', user=ORMUser{userId=3, name='叶星云', sex='女', age=31, salary=6890.0, borthday=Mon Feb 27 00:00:00 CST 1989}}
