【Mybatis】一对一实例

①创建数据库和表，数据库为mytest，表为father和child

DROP TABLE IF EXISTS child;
DROP TABLE IF EXISTS father;

CREATE TABLE child(
    child_id INT PRIMARY KEY auto_increment NOT NULL,
    child_name VARCHAR(20)
);

CREATE TABLE father(
    father_id INT PRIMARY KEY auto_increment NOT NULL,
    father_name VARCHAR(20),
    child_id INT
);

ALTER TABLE father ADD CONSTRAINT fk_child_id FOREIGN KEY (child_id) REFERENCES child(child_id);

INSERT INTO child(child_name) VALUES ("Guo Xiang");
INSERT INTO child(child_name) VALUES ("Zhang Wuji");
INSERT INTO father(father_name, child_id) VALUES ("Guo Jing", 1);
INSERT INTO father(father_name, child_id) VALUES ("Zhang Cuishan", 2);

②创建Java工程，导入相应的jar包

③创建配置文件conf.xml和数据库配置文件db.properties

<?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="db.properties"></properties>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${name}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    
    
    <mappers>
        <mapper resource="org/mybatis/mapping/fatherMapper.xml"/>
    </mappers>
</configuration>

driver = com.mysql.jdbc.Driver
url = jdbc:mysql://localhost:3306/mytest
name = root
password = root

④创建实体类Father和Child

package org.mybatis.domain;

public class Child {

    private int child_id;
    private String child_name;
    
    public int getChild_id() {
        return child_id;
    }
    public void setChild_id(int child_id) {
        this.child_id = child_id;
    }
    public String getChild_name() {
        return child_name;
    }
    public void setChild_name(String child_name) {
        this.child_name = child_name;
    }
    
    @Override
    public String toString() {
        return "[Child = child_id:" + child_id + ", child_name:" + child_name + "]";
    }
    
    
}

package org.mybatis.domain;

public class Father {

    private int father_id;
    private String father_name;
    private Child child;
    
    public int getFather_id() {
        return father_id;
    }
    public void setFather_id(int father_id) {
        this.father_id = father_id;
    }
    public String getFather_name() {
        return father_name;
    }
    public void setFather_name(String father_name) {
        this.father_name = father_name;
    }

    public Child getChild() {
        return child;
    }
    public void setChild(Child child) {
        this.child = child;
    }
    @Override
    public String toString() {
        return "[Father = father_id:" + father_id + ", father_name:" + father_name 
                + ", child:" + child + "]";
    }
    
    
}

⑤创建sql映射文件fatherMapper.xml

<?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="org.mybatis.mapping.fatherMapper">
    
    <!-- 方式一：嵌套结果 -->
<!--     <select id="getChild" parameterType="int" resultMap="ChildMap"> -->
<!--         select * from child c, father f where c.child_id = f.child_id and f.father_id=#{id} -->
<!--     </select> -->
    
<!--     <resultMap type="org.mybatis.domain.Father" id="ChildMap"> -->
<!--         <id property="father_id" column="father_id"/> -->
<!--         <result property="father_name" column="father_name" /> -->
<!--         <association property="child" javaType="org.mybatis.domain.Child"> -->
<!--             <id property="child_id" column="child_id"/> -->
<!--             <result property="child_name" column="child_name"/> -->
<!--         </association> -->
<!--     </resultMap> -->
    
    <!-- 方式二：嵌套查询 -->
    <select id="getChild" parameterType="int" resultMap="ChildMap">
        select * from father where father_id=#{id}
    </select>
    
    <resultMap type="org.mybatis.domain.Father" id="ChildMap">
        <id property="father_id" column="father_id"/>
        <result property="father_name" column="father_name" />
        <collection property="child" column="child_id" select="getChildCollection">
        </collection>
    </resultMap>
    
    <select id="getChildCollection" resultType="org.mybatis.domain.Child">
        select * from child where child_id=#{child_id}
    </select>
    
</mapper>

⑥向配置文件中注册 fatherMapper.xml 文件【已添加，查看第③步】

⑦测试类

package org.mybatis.app;

import java.io.InputStream;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import org.mybatis.domain.Father;

public class TestOneToOne {

    SqlSession session;
    
    @Before
    public void beforeLoad() {
        InputStream inputStream = 
                TestOneToOne.class.getClassLoader().getResourceAsStream("conf.xml");
        SqlSessionFactory sqlSessionFactory = 
                new SqlSessionFactoryBuilder().build(inputStream);
        session = sqlSessionFactory.openSession();
    }
    
    
    @Test
    public void testOneToOne() {
        // 根据fatherID得到child
        String statement = "org.mybatis.mapping.fatherMapper.getChild";
        Father father = session.selectOne(statement,2);
        session.close();
        System.out.println(father.getFather_name() + "'s child is "
                + father.getChild().getChild_name());
    }
}

⑧结构图

 fatherMapper.xml中有两种方式，两种方式的结果一样