整合MyBatis

1、新增项目时要选择，MyBatis Framework，MySQL Driver

image.png

2、application.yml文件设置数据源参数

  1. #2、配置相关信息
  2. spring:
  3.   datasource:
  4.     driver-class-name: com.mysql.cj.jdbc.Driver
  5.     url: jdbc:mysql://localhost:3307/jakedeal?serverTimezone=UTC
  6.     username: root
  7.     password: XXXXX
  8.   main:
  9. #    关闭logo图像
  10.     banner-mode: off
  1. MySQL8.x驱动强制要设置时区
  2. 修改url,，添加serverTimezone设定
  3. 驱动类过时，提醒更换为com.mysql.cj.jdbc.Driver

    3、定义数据层接口与映射配置

    ```java package com.tj.domain;

public class User { private Integer id; private String user_id; private String user_name;

  1. @Override
  2. public String toString() {
  3.     return "User{" +
  4.             "id=" + id +
  5.             ", user_id='" + user_id + '\'' +
  6.             ", user_name='" + user_name + '\'' +
  7.             '}';
  8. }
  10. public Integer getId() {
  11.     return id;
  12. }
  14. public void setId(Integer id) {
  15.     this.id = id;
  16. }
  18. public String getUser_id() {
  19.     return user_id;
  20. }
  22. public void setUser_id(String user_id) {
  23.     this.user_id = user_id;
  24. }
  26. public String getUser_name() {
  27.     return user_name;
  28. }
  30. public void setUser_name(String user_name) {
  31.     this.user_name = user_name;
  32. }

}

  1. ```java
  2. package com.tj.dao;
  4. import com.tj.domain.User;
  5. import org.apache.ibatis.annotations.Mapper;
  6. import org.apache.ibatis.annotations.Select;
  7. import org.springframework.stereotype.Repository;
  9. @Mapper
  10. @Repository
  11. public interface UserDao  {
  12.     @Select("select * from users where id=#{id}")
  13.     public User getById(Integer id);
  14. }

4、测试类中注入dao接口，测试功能

  1. package com.tj;
  3. import com.tj.dao.UserDao;
  4. import org.junit.jupiter.api.Test;
  5. import org.springframework.beans.factory.annotation.Autowired;
  6. import org.springframework.boot.test.context.SpringBootTest;
  8. @SpringBootTest
  9. class MybatisApplicationTests {
  12.     @Autowired
  13.     private UserDao userDao;
  15.     @Test
  16.     void contextLoads() {
  17.         System.out.println(userDao.getById(10049));
  18.     }
  20. }

问题报错解决

image.png
解决方法：Could not autowire.No beans of ‘XXXX‘type found的解决方法（详细解析其用法注解）

整合MyBatis-Plus

https://mvnrepository.com/artifact/com.baomidou/mybatis-plus-boot-starter/3.5.1

  1. <!--mybatis-plus依赖-->
  2. <dependency>
  3.     <groupId>com.baomidou</groupId>
  4.     <artifactId>mybatis-plus-boot-starter</artifactId>
  5.     <version>3.5.1</version>
  6. </dependency>

配置数据库

常见问题

Mybatis 查询出来的数据数量正确，但是带下划线的字段数据为null

参考：Mybatis 查询出来的数据数量正确，但是具体数据为null
解决方法一：配置文件（我喜欢这种，可以让数据库和JAVA里的名字统一，便于理解）

  1. mybatis-plus:
  2.   configuration:
  3.     map-underscore-to-camel-case: false

解决方法二：下划线“_”改成驼峰写法
参考：https://blog.csdn.net/weixin_41758407/article/details/90722718
java中使用驼峰命名
数据库表列：user_name
实体类属性：userName

@TableName(“user”)可以绑定表

  1. package com.tj.dao;
  3. import com.baomidou.mybatisplus.annotation.TableName;
  4. import com.baomidou.mybatisplus.core.mapper.BaseMapper;
  5. import com.tj.domain.Users;
  6. import org.apache.ibatis.annotations.Mapper;
  7. import org.springframework.stereotype.Repository;
  9. @Mapper
  10. @Repository
  11. @TableName("user")
  12. public interface UserDao extends BaseMapper<Users> {
  13. //    @Select("select * from users where id=#{id}")
  14. //    public Users getById(Integer id);
  15. }