Mybatis一对一映射详解编程语言

create table cards( 
    id    int(5)    primary key, 
    num varchar(20) 
); 
create table students( 
    id    int(5)    primary key, 
    name varchar(10), 
    cid int(5), 
    constraint cid_fk foreign key(cid) references cards(id) 
);

insert into cards(id,num) values(2,’12345′);
insert into students(id,name,cid) values(1,’cat’,2);

package com.jyk.mybatis.oneByone; 
 
public class Card { 
 
    private int cid;            //身份证id 
    private String cnum;        //身份证号码 
     
    public int getCid() { 
        return cid; 
    } 
    public void setCid(int cid) { 
        this.cid = cid; 
    } 
    public String getCnum() { 
        return cnum; 
    } 
    public void setCnum(String cnum) { 
        this.cnum = cnum; 
    } 
     
}

package com.jyk.mybatis.oneByone; 
 
public class Student { 
 
    private int id;                //学生id 
    private String name;        //学生姓名 
    private Card card;            //身份证信息 
     
    public int getId() { 
        return id; 
    } 
    public void setId(int id) { 
        this.id = id; 
    } 
    public String getName() { 
        return name; 
    } 
    public void setName(String name) { 
        this.name = name; 
    } 
    public Card getCard() { 
        return card; 
    } 
    public void setCard(Card card) { 
        this.card = card; 
    } 
}

<?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"> 
 
<!-- 名称空间namespace必须唯一 --> 
<mapper namespace="studentNamespace"> 
     
    <!--  
        resultMap标签：映射实体与表 
        type属性:实体全路径名 
        id属性:为实体与表的映射取一个唯一的编号 
     --> 
    <resultMap type="student" id="studentMap"> 
        <!--  
        id标签:映射主键属性 
        result标签：映射非主键属性 
        property属性:实体属性名 
        column属性：表的字段名 
         --> 
        <id property="id" column="id"/> 
        <result property="name" column="name"/> 
        <association property="card" resultMap="cardNamespace.cardMap"/> 
    </resultMap> 
 
    <!-- 根据学生id找到对应学生信息和身份证信息 --> 
    <select id="findById" parameterType="int" resultMap="studentMap"> 
        select s.id,s.name,c.id as cid,c.num as cnum 
        from students s inner join cards c 
        on s.cid = c.id  
        and s.id = #{id} 
    </select> 
</mapper>

<?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"> 
 
<!-- 名称空间namespace必须唯一 --> 
<mapper namespace="cardNamespace"> 
     
    <!--  
        resultMap标签：映射实体与表 
        type属性:实体全路径名 
        id属性:为实体与表的映射取一个唯一的编号 
     --> 
    <resultMap type="card" id="cardMap"> 
        <!--  
        id标签:映射主键属性 
        result标签：映射非主键属性 
        property属性:实体属性名 
        column属性：表的字段名 
         --> 
        <id property="cid" column="cid"/> 
        <result property="cnum" column="cnum"/> 
    </resultMap> 
</mapper>

<?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> 
<!-- 加载类路径下的属性文件 --> 
<properties resource="db.properties"> 
</properties> 
<!-- 设置类型别名 --> 
<typeAliases> 
<typeAlias type="com.jyk.mybatis.oneByone.Card" alias="card"/> 
<typeAlias type="com.jyk.mybatis.oneByone.Student" alias="student"/> 
</typeAliases> 
<!-- 设置一个默认的连接环境信息 --> 
<environments default="mysql_env"> 
<!-- 连接环境信息，取一个唯一的编号 --> 
<environment id="mysql_env"> 
<!-- mybatis使用的jdbc事务管理方式 --> 
<transactionManager type="jdbc"> 
</transactionManager> 
<!-- mybatis使用连接池方式来获取链接 --> 
<dataSource type="pooled"> 
<!-- 配置与数据库交互的四个属性 --> 
<property name="driver" value="${mysql.driver}"/> 
<property name="url" value="${mysql.url}"/> 
<property name="username" value="${mysql.username}"/> 
<property name="password" value="${mysql.password}"/> 
</dataSource> 
</environment> 
</environments> 
<mappers> 
<mapper resource="com/jyk/mybatis/oneByone/StudentMapper.xml"/> 
<mapper resource="com/jyk/mybatis/oneByone/CardMapper.xml"/> 
</mappers> 
</configuration>

package com.jyk.mybatis.oneByone; 
import org.apache.ibatis.session.SqlSession; 
import com.jyk.mybatis.util.MyBatisUtil; 
public class StudentDao { 
/* 
* 根据ID查找 
*/ 
public Student findById(int id) 
{ 
SqlSession sqlSession = null; 
try{ 
sqlSession = MyBatisUtil.getSqlSession(); 
Student stu = sqlSession.selectOne("studentNamespace.findById", id); 
return stu; 
}catch(Exception e){ 
e.printStackTrace(); 
throw e; 
}finally{ 
MyBatisUtil.closeSqlSession(); 
} 
} 
public static void main(String[] args) { 
StudentDao sd = new StudentDao(); 
Student stu = sd.findById(1); 
System.out.println("id=="+stu.getId()); 
System.out.println("name=="+stu.getName()); 
System.out.println("cid=="+stu.getCard().getCnum()); 
} 
}