一、创建部门表和员工表：
创建部门信息表`t_department`，其中包括`id`, `name`
CREATE TABLE t_department (
id INT AUTO_INCREMENT,
name VARCHAR(20) UNIQUE NOT NULL,
PRIMARY KEY(id)
) DEFAULT CHARSET=UTF8;
往部门表中插入数据：
INSERT INTO t_department (name) VALUES
(‘UI‘), (‘RD‘), (‘TEST‘);
创建员工信息表t_user
CREATE TABLE t_user(
id INT PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(20) ,
password VARCHAR(20) ,
age int ,
phone VARCHAR(20) ,
email VARCHAR(20) ,
is_Delete int
)DEFAULT CHARSET=UTF8;
往员工表中插入数据：
INSERT
INTO t_user
VALUES(null,‘张三‘,‘123456‘,23,‘110‘,‘11111@qq.com‘,1),(null,‘历史‘,‘123456‘,23,‘110‘,‘11111@qq.com‘,1),(null,‘孙悟空‘,‘123456‘,23,‘110‘,‘11111@qq.com‘,2),(null,‘李白‘,‘123456‘,23,‘110‘,‘11111@qq.com‘,2),(null,‘八戒‘,‘123456‘,23,‘110‘,‘11111@qq.com‘,2);
插入数据错误：
https://www.cnblogs.com/package-java/p/10494380.html
在查询时，`<select>`节点必须指定结果的类型，可以通过`resultType`属性来指定，也可以通过`resultMap`属性来指定。
当有直接对应的查询结果时，可以使用`resultType`，取值一般是实体类的类型，或VO类的类型。
某些查询可能需要将查询结果进行特殊的封装，例如查询时存在1对多、多对多、多对1等关系，则需要使用`resultMap`来配置封装的方式。
二、创建实体类：
1、Vo类的实体类，因为部门只有三个，三个部门里面可能有很多员工，所以把员工封装到List集合中，由于将多条信息明细存储到了list中，因此查询后将不再出现重复数据，达到了去重的效果
package cn.tedu.mybatis.vo;
import java.io.Serializable;
import java.util.List;
import cn.tedu.mybatis.entity.User;
public class DepartmentVO implements Serializable {
private static final long serialVersionUID = -6442405812964981459L;
private Integer did;
private String name;
private List<User> users;
public Integer getDid() {
return did;
}
public void setDid(Integer did) {
this.did = did;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<User> getUsers() {
return users;
}
public void setUsers(List<User> users) {
this.users = users;
}
@Override
public String toString() {
return "DepartmentVO [did=" + did + ", name=" + name + ", users=" + users + "]";
}
}
2、员工类：
package cn.tedu.mybatis.entity;
import java.io.Serializable;
public class User implements Serializable {
private static final long serialVersionUID = 7323921614984096421L;
private Integer id;
private String username;
private String password;
private Integer age;
private String phone;
private String email;
private Integer isDelete;
private Integer did;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public Integer getIsDelete() {
return isDelete;
}
public void setIsDelete(Integer isDelete) {
this.isDelete = isDelete;
}
public Integer getDid() {
return did;
}
public void setDid(Integer did) {
this.did = did;
}
@Override
public String toString() {
return "User [id=" + id + ", username=" + username + ", password=" + password + ", age=" + age + ", phone="
+ phone + ", email=" + email + ", isDelete=" + isDelete + ", did=" + did + "]";
}
}
三、创建接口和抽象方法：
package cn.tedu.mybatis.mapper;
import cn.tedu.mybatis.vo.DepartmentVO;
public interface DepartmentMapper {
DepartmentVO findById(Integer id);
}
四、SQL语句的映射：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//ibatis.apache.org//DTD Mapper 3.0//EN"
"http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">
<mapper namespace="cn.tedu.mybatis.mapper.DepartmentMapper">
<!-- namespace：抽象类绝对路径 -->
<resultMap id="Department_VO_Map"
type="cn.tedu.mybatis.vo.DepartmentVO"> <!-- id节点：配置主键 -->
<!-- type：实体类绝对路径 -->
<!-- column：查询结果中的列名 -->
<!-- property：以上type属性对应的数据类型中的属性名（类里面的属性） -->
<id column="did" property="did"/>
<!-- result节点：配置普通字段 -->
<result column="name" property="name"/>
<!-- collection节点：配置List集合类型的属性，用于1对多的查询 -->
<!-- ofType：在List里放的是什么类型 -->
<collection property="users"
ofType="cn.tedu.mybatis.entity.User">
<id column="uid" property="id"/>
<result column="username" property="username"/>
<result column="password" property="password"/>
<result column="age" property="age"/>
<result column="phone" property="phone"/>
<result column="email" property="email"/>
<result column="isDelete" property="isDelete"/>
</collection>
</resultMap>
<select id="findById"
resultMap="Department_VO_Map">
SELECT
t_department.id AS did,
name,
t_user.id AS uid,
username,
password,
age,
phone,
email,
is_delete
FROM
t_department
INNER JOIN
t_user
ON
t_user.did=t_department.id
WHERE
t_department.id=#{id}
</select>
</mapper>
> 以上代码中，自定义别名是因为需要区分查询结果中的列的名称，并不是因为需要与数据类型中的属性对应，关于查询结果的列名与数据类型的属性名的对应，可以通过`<resultMap>`中的配置来完成！
五、测试：
package cn.tedu.mybatis.mapper;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import cn.tedu.mybatis.vo.DepartmentVO;
public class DepartmentMapperTestCase {
AbstractApplicationContext ac;
DepartmentMapper mapper;
@Before
public void doBefore() {
ac = new ClassPathXmlApplicationContext("spring-dao.xml");
mapper = ac.getBean("departmentMapper", DepartmentMapper.class);
}
@After
public void doAfter() {
ac.close();
}
@Test
public void findById() {
Integer id = 2;
DepartmentVO data
= mapper.findById(id);
System.out.println(data);
}
}
原文地址：https://www.cnblogs.com/package-java/p/10495912.html