表一对一关联（[尚硅谷]_张晓飞_Mybatis 学习笔记三）

CREATE TABLE teacher(
t_id INT PRIMARY KEY AUTO_INCREMENT,
t_name VARCHAR(20)
);
CREATE TABLE class(
c_id INT PRIMARY KEY AUTO_INCREMENT,
c_name VARCHAR(20),
teacher_id INT
);
ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id);

INSERT INTO teacher(t_name) VALUES('LS1');
INSERT INTO teacher(t_name) VALUES('LS2');

INSERT INTO class(c_name, teacher_id) VALUES('bj_a', 1);
INSERT INTO class(c_name, teacher_id) VALUES('bj_b', 2);

package com.hb.bean;

public class Classes {
private int id;
private String name;
private Teacher teacher;
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 Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
@Override
public String toString() {
return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + "]";
}

}

package com.hb.bean;

public class Teacher {
private int id;
private String name;
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;
}
@Override
public String toString() {
return "Teacher [id=" + id + ", name=" + name + "]";
}

}

<?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.hb.bean.classesMapper">
<!-- 这里namespace必须是“包名 + xml文件名”，不然要运行的时候要报错 “is not known to the MapperRegistry” -->

<!-- 方式一：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集 封装联表查询的数据(去除重复的数据) select * from class
c, teacher t where c.teacher_id=t.t_id and c.c_id=1 -->
<select id="getClass" parameterType="int" resultMap="ClassResultMap">
select *
from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
</select>

<resultMap type="com.hb.bean.Classes" id="ClassResultMap">
<id property="id" column="c_id" />
<result property="name" column="c_name" />
<association property="teacher" javaType="com.hb.bean.Teacher">
<id property="id" column="t_id" />
<result property="name" column="t_name" />
</association>
</resultMap>

<!-- 方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型 SELECT * FROM class WHERE c_id=1;
SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值 -->

<select id="getClass2" parameterType="int" resultMap="ClassResultMap2">
select *
from class where c_id=#{id}
</select>
<resultMap type="com.hb.bean.Classes" id="ClassResultMap2">
<id property="id" column="c_id" />
<result property="name" column="c_name" />
<association property="teacher" column="teacher_id"
select="getTeacher">
</association>
</resultMap>

<select id="getTeacher" parameterType="int" resultType="com.hb.bean.Teacher">
SELECT
t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>

</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>

<settings>
<!-- changes from the defaults for testing -->
<setting name="cacheEnabled" value="false" />
<setting name="useGeneratedKeys" value="true" />
<setting name="defaultExecutorType" value="REUSE" />
</settings>

<environments default="development">
<environment id="development">
<transactionManager type="jdbc" />
<dataSource type="POOLED">
<!--
<property name="driver" value="oracle.jdbc.driver.OracleDriver"/>
<property name="url" value="jdbc:oracle:thin:@192.168.56.201:1521:system"/>
-->
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
<property name="username" value="root" />
<property name="password" value="123456" />
</dataSource>
</environment>
</environments>

<mappers>
<mapper resource="com/hb/bean/classesMapper.xml" />
</mappers>

</configuration>

package com.hb.test3;

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 com.hb.bean.Classes;

public class Test3 {

public static SqlSessionFactory sqlSessionFactory;
public static SqlSession sqlSession;

@Before
public void init(){
//"/"表示是在src根目录下
String source = "config.xml";
InputStream inputStream = Test3.class.getClassLoader().getResourceAsStream(source);

try {
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//			sqlSession = sqlSessionFactory.openSession();
//是否自动提交，默认不是自动提交的
sqlSession = sqlSessionFactory.openSession(true);
} catch (Exception e) {
e.printStackTrace();
}
}

@Test
public void selectById(){
String statment = "com.hb.bean.classesMapper.getClass";
Classes classes = sqlSession.selectOne(statment, 1);
System.out.println(classes);
}

@Test
public void selectById2(){
String statment = "com.hb.bean.classesMapper.getClass2";
Classes classes = sqlSession.selectOne(statment, 1);
System.out.println(classes);
}

}