Mybatis框架学习笔记
Posted 小智RE0
tags:
篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了Mybatis框架学习笔记相关的知识，希望对你有一定的参考价值。
本篇Mybatis框架学习笔记;紧跟之前的学习
Mybatis框架学习笔记(3)–>
文章目录
本次笔记整理
resultMap的使用 ;
mybatis3.0的文档–>https://mybatis.org/mybatis-3/zh/sqlmap-xml.html
1.当出现数据库的列字段与实体类的不一致时;需要手动配置字段映射;
在之前的基础上,
这次直接给用户数据表添加一个新的字段;info表示信息;
但是,实体类这边我在添加这个属性时,故意把它的属性名定义为information
package com.xiaozhi.pojo;
/**
* @author by CSDN@小智RE0
* @date 2021-10-27 1:48
* 实体类User(用户类)
*/
public class User {
//属性,id,账户,密码,地址;
private int id;
private String account;
private String password;
private String addRess;
//添加的信息属性; 注意这里的属性名和数据库的列字段名完全不一致;
private String information;
//构造方法;
public User() {
}
public User(int id, String account, String password, String addRess, String information) {
this.id = id;
this.account = account;
this.password = password;
this.addRess = addRess;
this.information = information;
}
//这里构造方法初始化时就没包括ID;
public User(String account, String password, String addRess, String information) {
this.account = account;
this.password = password;
this.addRess = addRess;
this.information = information;
}
//为信息 information 添加getter setter方法;
public String getInformation() {
return information;
}
public void setInformation(String information) {
this.information = information;
}
//getter,setter;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getAccount() {
return account;
}
public void setAccount(String account) {
this.account = account;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getAddRess() {
return addRess;
}
public void setAddRess(String addRess) {
this.addRess = addRess;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", account='" + account + '\\'' +
", password='" + password + '\\'' +
", addRess='" + addRess + '\\'' +
", information='" + information + '\\'' +
'}';
}
}
这里的持久层接口;本次笔记整理,就先把之前定义的方法去掉;保留一个查询所有用户的方法;
package com.xiaozhi.mapper;
import com.xiaozhi.pojo.User;
import java.util.List;
/**
* @author by CSDN@小智RE0
* @date 2021-10-24 22:23
* 持久层映射接口
*/
public interface UserMapper {
//查询所有用户;
List<User> findUser();
}
持久层映射配置文件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">
<!--注意 这里对应空间为持久层映射接口-->
<mapper namespace="com.xiaozhi.mapper.UserMapper">
<!--查询所有用户-->
<select id="findUser" resultType="user">
select * from t_user
</select>
</mapper>
核心配置文件mybatis-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>
<!--引入外部的资源文件-->
<properties resource="database.properties">
</properties>
<settings>
<!--配置日志-->
<setting name="logImpl" value="LOG4J"/>
<!--设置开启驼峰命名匹配-->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!--配置别名-->
<typeAliases>
<!--为实体类User配置别名为user-->
<typeAlias type="com.xiaozhi.pojo.User" alias="user"/>
</typeAliases>
<!-- environments 环境配置 , 这里的default来指定默认使用的环境变量 -->
<environments default="development">
<!-- environment 环境变量 ;可以写多个,尽量保证id不重名就行-->
<!--开发的环境变量-->
<environment id="development">
<!--事务管理-->
<transactionManager type="JDBC">
</transactionManager>
<!--dataSource:数据源-->
<dataSource type="UNPOOLED">
<!--数据库驱动,url连接,数据库账户,密码-->
<property name="driver" value="${driver}" />
<property name="url" value="${url}"/>
<property name="username" value="${username}" />
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!--配置mapper映射-->
<mappers>
<mapper resource="mapper/UserMapper.xml"/>
</mappers>
</configuration>
外部数据库链接资源database.properties
driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/day20211024_study_mybatis_db?characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai
username=root
password=123456
这时,去测试的话;
//查询所有用户;
@Test
public void findAllUser(){
//使用工具类创建sqlSession;
SqlSession sqlSession = MyBatisUtils.getSqlSession();
//获取代理对象;
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
//调用方法;
List<User> user = userMapper.findUser();
//以流的方式遍历;
user.forEach(System.out::println);
//关闭sqlSession;
sqlSession.close();
}
查询时注意到info信息这一列查出来全是null空值
那么就得请出resultMap结果集映射了;它的ID是唯一标识符;
然后,它里面的<id>标签主要用来配置主键的映射;<result>标签配置非主键的映射;
column用来配置数据表的列字段名;然后property用来配置实体类的属性名;
那么只需要在UserMapper.xml文件中进行配置;
<?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">
<!--注意 这里对应空间为持久层映射接口-->
<mapper namespace="com.xiaozhi.mapper.UserMapper">
<!--可配置resultMap 进行数据库的列字段名与类的属性字段相对应-->
<resultMap id="userMap" type="user">
<!--ID,主键映射-->
<id column="id" property="id"/>
<!--其他列的映射-->
<result column="account" property="account"/>
<result column="password" property="password"/>
<result column="add_ress" property="addRess"/>
<result column="info" property="information"/>
</resultMap>
<!--查询所有用户; 这里的resultMap直接用id指向即可-->
<select id="findUser" resultMap="userMap">
select * from t_user
</select>
</mapper>
同样地,再去查询所有用户,信息就有显示了
2.两张表以上的多表映射;
首先,去新建两张表;部门表;员工表
-- 创建部门表;
CREATE TABLE IF NOT EXISTS t_dept(
`id` INT PRIMARY KEY AUTO_INCREMENT COMMENT 'Id',
`name` VARCHAR(15) COMMENT '部门名称',
-- 这里的操作人ID是来自于之前的用户表,
`optionId` INT COMMENT '操作人Id'
);
-- 创建员工表;
CREATE TABLE IF NOT EXISTS t_employee(
`id` INT PRIMARY KEY AUTO_INCREMENT COMMENT 'ID',
`name` VARCHAR(15) COMMENT '员工姓名',
`sex` char(1),
`deptID` INT COMMENT '部门ID',
-- 这里的操作人ID是来自于之前的用户表,
`optionId` INT COMMENT '操作人Id'
);
简单地存入一点数据;
部门表
员工表
OK,直接去pojo包下创建员工类;部门类;
package com.xiaozhi.pojo;
/**
* @author by CSDN@小智RE0
* @date 2021-10-29 19:49
* 员工实体类;
*/
public class Employee {
private int id;
private String name;
private String sex;
//关联着部门和用户;
private Dept dept;
private User user;
//构造方法;
public Employee() {
}
public Employee(String name, String sex, Dept dept, User user) {
this.name = name;
this.sex = sex;
this.dept = dept;
this.user = user;
}
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 String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Dept getDept() {
return dept;
}
public void setDept(Dept dept) {
this.dept = dept;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
@Override
public String toString() {
return "Employee{" +
"id=" + id +
", name='" + name + '\\'' +
", sex='" + sex + '\\'' +
", dept=" + dept +
", user=" + user +
'}';
}
}
部门类
package com.xiaozhi.pojo;
import java.util.List;
/**
* @author by CSDN@小智RE0
* @date 2021-10-29 19:41
* 部门表;
*/
public class Dept {
private int id;
private String name;
//关联员工;
private List<Employee> employees;
//关联操作的用户;
private User user;
public Dept() {
}
public Dept(String name, List<Employee> employees, User user) {
this.name = name;
this.employees = employees;
this.user = user;
}
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 List<Employee> getEmployees() {
return employees;
}
public void setEmployees(List<Employee> employees) {
this.employees = employees;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
@Override
public String toString() {
return "Dept{" +
"id=" + id +
", name='" + name + '\\'' +
", employees=" + employees +
", user=" + user +
'}';
}
}
在mybatis的核心配置文件mybatis-config.xml中先去配置别名
<!--配置别名-->
<typeAliases>
<!--为实体类User配置别名为user-->
<typeAlias type="com.xiaozhi.pojo.User" alias="user"/>
<!--为实体类员工类配置别名-->
<typeAlias type="com.xiaozhi.pojo.Employee" alias="employee"/>
<!--为部门的实体类配置别名-->
<typeAlias type="com.xiaozhi.pojo.Dept" alias="dept"/>
</typeAliases>
完成查询所有的员工(附带地查到员工对应的部门);注意有一对一的关系;
在mapper包下创建EmployeeMapper持久层接口;创建查询员工的方法;
package com.xiaozhi.mapper;
import com.xiaozhi.pojo.Employee;
import java.util.List;
/**
* @author by CSDN@小智RE0
* @date 2021-10-29 20:28
*/
public i以上是关于Mybatis框架学习笔记的主要内容，如果未能解决你的问题，请参考以下文章