MyBatis的一对一

1. 建立好工程后，在pom.xml中配置myBatis的依赖。

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.whl</groupId>
    <artifactId>MyBatis02</artifactId>
    <packaging>war</packaging>
    <version>0.0.1-SNAPSHOT</version>
    <name>MyBatis02 Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.4</version>
        </dependency>
    </dependencies>
    <build>
        <finalName>MyBatis02</finalName>
    </build>
</project>

主要就是加一个MyBatis的依赖，以及修改一下Junit的版本，以适应自己的环境。

2 新建一个Card类和一个Person类，每一个Person只有一个Card。故在Person类中

会有一个Card类的属性，在建立数据库时，cid作为外键，存在于Person表中。代码如下：

数据库在dos框中自己建立（cid int unique , foreign key (cid) references card (cid)）(外键设置)

Card类代码如下

package com.whl.one2one;

public class Card {
    private int cid;
    private String cnumber;
    public int getCid() {
        return cid;
    }
    public void setCid(int cid) {
        this.cid = cid;
    }
    public String getCnumber() {
        return cnumber;
    }
    public void setCnumber(String cnumber) {
        this.cnumber = cnumber;
    }
    public Card(int cid, String cnumber) {
        super();
        this.cid = cid;
        this.cnumber = cnumber;
    }
    public Card() {
        super();
    }
    @Override
    public String toString() {
        return "Card [cid=" + cid + ", cnumber=" + cnumber + "]";
    }

}

Person类代码如下：

package com.whl.one2one;

public class Person {
    private int pid;
    private String pname;
    private String page;
    private String psex;
    private Card card;
    public int getPid() {
        return pid;
    }
    public void setPid(int pid) {
        this.pid = pid;
    }
    public String getPname() {
        return pname;
    }
    public void setPname(String pname) {
        this.pname = pname;
    }
    public String getPage() {
        return page;
    }
    public void setPage(String page) {
        this.page = page;
    }
    public String getPsex() {
        return psex;
    }
    public void setPsex(String psex) {
        this.psex = psex;
    }
    public Card getCard() {
        return card;
    }
    public void setCard(Card card) {
        this.card = card;
    }
    @Override
    public String toString() {
        return "Person [pid=" + pid + ", pname=" + pname + ", page=" + page + ", psex=" + psex + ", card=" + card + "]";
    }
    public Person(int pid, String pname, String page, String psex, Card card) {
        super();
        this.pid = pid;
        this.pname = pname;
        this.page = page;
        this.psex = psex;
        this.card = card;
    }
    public Person() {
        super();
    }

}

3.在建立好上述的Jopo类后，在同样的包下新建CardMapper.xml和PersonMapper.xml来映射SQL语句。

CardMapper.xml代码如下：

<?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.whl.one2one">
  <select id="selectCardByID" parameterType="int" resultType="com.whl.one2one.Card">
    select * from card where cid = #{id}
  </select>
</mapper>

PersonMapper.xml代码如下：在Person类中，存在主外键关系，所以select中不在是单一表的查询，将原本的resultType改为

resultMap，其中的值，就是后续Resultmap的ID。且在resultMap中会存在一个对CardMapper.xml的调用。

<?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.whl.one2one">

          <select id="selectPersonById" parameterType="int" resultMap="resultPersonMap">
              select * from tb_person where pid=#{id}
          </select>

          <resultMap id="resultPersonMap" type="com.whl.one2one.Person">
            <id property="pid" column="pid" />
            <result property="pname" column="name" />
            <result property="psex" column="psex" />
            <result property="page" column="page" />
            <association property="card" column="cid"
                select="com.whl.one2one.selectCardByID"
                javaType="com.whl.one2one.Card"/>
          </resultMap >

  </mapper>

4. 在myBatis-config.xml 中实现与数据库的连接。当然在连接之前需要数据库的Jar包，网速好时可在pom中添加依赖自动下载

网速不好使要手动加载。在代码中可以看到连接数据库的driver、url、user、pass等都是通过<properties resource="jdbc.properties"/>来加载资源从而获得的。jdbc.properties文件后面会展示。同时在此XML文件中还需要完成对CardMapper.xml以及PersonMapper.xml的映射。如<Mapper>节点所示。

<?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>
     <!--加载资源 -->
      <properties resource="jdbc.properties"/>

      <environments default="mybatis">
          <environment id="mybatis">
              <transactionManager type="JDBC"/>
              <dataSource type="POOLED">
                  <property name="driver" value="${jdbc.driver}" />
                <property name="url" value="${jdbc.url}" />
                <property name="username" value="${jdbc.user}" />
                <property name="password" value="${jdbc.pass}" />
              </dataSource>
          </environment>
      </environments>
      <mappers>
          <mapper resource="com/whl/one2one/CardMapper.xml"></mapper>
          <mapper resource="com/whl/one2one/PersonMapper.xml"></mapper>
      </mappers>
  </configuration>

5 测试：测试代码如下所示：利用Junit的before和After来实现前期session的准备和后期session的关闭。

package com.whl.testone2one;

import java.io.IOException;
import java.io.InputStream;

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 org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.whl.one2one.Card;
import com.whl.one2one.Person;

public class TestOne2One {
    private SqlSession s;
    @Before
    public void beforeTest(){
        String res = "mybatis-config.xml";

        try {
            InputStream is = Resources.getResourceAsStream(res);

            SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(is);

            s = ssf.openSession();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void testPersonById(){
        Person p = s.selectOne("com.whl.one2one.selectPersonById",1);
        System.out.println(p);
    }
    @Test
    public void testCardById(){
        Card c = s.selectOne("com.whl.one2one.selectCardByID",1);
        System.out.println(c);
    }

    @After
    public void afterTest(){

            s.commit();
            if(s != null){
                s.close();
                s = null;
            }

    }
}