Mybatis快速上手4 关联表查询二：一对多表关联查询

Mybatis快速上手4 一对多表关联查询

环境：Eclipse+Tomcat9+JDK10+Mybatis-3.1.1、Navicat
需求
代码
结果

其他章节及开发包：https://blog.youkuaiyun.com/XIMAX/article/details/106255196

环境：Eclipse+Tomcat9+JDK10+Mybatis-3.1.1、Navicat

在这里插入图片描述
test1~8分别对应八章，本章使用包test4、tool，文件config.xml、db.properties、log4j.properties

需求

根据classId查询对应的班级信息,包括学生,老师

代码

建库，建表

CREATE TABLE student(
 s_id INT PRIMARY KEY AUTO_INCREMENT, 
 s_name VARCHAR(20), 
 class_id INT
);

INSERT INTO student(s_name, class_id) VALUES('xs_A', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_B', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_C', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_D', 2);
INSERT INTO student(s_name, class_id) VALUES('xs_E', 2);
INSERT INTO student(s_name, class_id) VALUES('xs_F', 2);

config.xml

<?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>
  <typeAliases>
    <package name="com.rjxy.test4"/>
 <typeAliases>
 
 <typeAliases>
   <package name="com.rjxy.test2"/>
 <typeAliases>
 <environments default="development">
   <environment id="development">
    <transactionManager type="JDBC" />
    <dataSource type="POOLED">
     <property name="driver" value="${driver}" />
     <property name="url" value="${url}" />
     <property name="username" value="${username}" />
     <property name="password" value="${password}" />
    </dataSource>
   </environment>
  </environments>  
 
 <mappers>
   <mapper resource="com/rjxy/test4/userMapper.xml"/>
 <mappers>
</configuration>

userMapper.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="com.rjxy.test4.userMapper">
<!-- 一对多关联 method1 联表查询 -->
 <select id="getClass" parameterType="int" resultMap="getClassMap">
  select * from class c,teacher t, student s where c.teacher_id=t.t_id and c.c_id=s.class_id and c.c_id=#{id}
 </select>
 
<resultMap type="Classes2" id="getClassMap">
  <id property="id" column="c_id"/>
  <result property="name" column="c_name"/>
  <association property="teacher" javaType="Teacher">
   <id property="id" column="t_id"/>
   <result property="name" column="t_name"/>
  </association>
  <collection property="students" ofType="Student">
   <id property="id" column="s_id"/>
   <result property="name" column="s_name"/>
  </collection>
 </resultMap> 

!-- method2 嵌套查询 -->