【MyBatis快速入门】MyBatis编程流程

• 0.把数据导入数据库
• 1.下载依赖包
• 2.写配置文件
• 3.写代码访问数据库里的数据
• • 3.1 实体类
  • 3.2 dao数据访问层
  • 3.3 xml配置文件
  • 3.4 测试

C:Users9>mysql -uroot -p***
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or g.
Your MySQL connection id is 10
Server version: 8.0.26 MySQL Community Server - GPL

Copyright (c) 2000, 2021, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| bjpowernode        |
| community          |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
6 rows in set (0.00 sec)

mysql> drop database community ;
Query OK, 5 rows affected (0.18 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| bjpowernode        |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> create database community;
Query OK, 1 row affected (0.02 sec)

mysql> use community;
Database changed
mysql> source D:codeinit_schema.sql
Query OK, 0 rows affected (0.00 sec)
...
Query OK, 0 rows affected (0.00 sec)

mysql> show tables;
+---------------------+
| Tables_in_community |
+---------------------+
| comment             |
| discuss_post        |
| login_ticket        |
| message             |
| user                |
+---------------------+
5 rows in set (0.00 sec)

mysql> source D:codeinit_data.sql;
ERROR:
Unknown command 'i'.
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'odeinit_data.sql' at line 1
mysql> source D:/code/init_data.sql;
Query OK, 0 rows affected (0.00 sec)
...
Query OK, 0 rows affected (0.00 sec)

https://mvnrepository.com/

# DataSourceProperties
#驱动
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver 
#连接格式
spring.datasource.url=jdbc:mysql://localhost:3306/community?characterEncoding=utf-8&useSSL=false&serverTimezone=Hongkong
spring.datasource.username=root
#1.写自己的密码
spring.datasource.password=
spring.datasource.type=com.zaxxer.hikari.HikariDataSource
spring.datasource.hikari.maximum-pool-size=15
spring.datasource.hikari.minimum-idle=5
spring.datasource.hikari.idle-timeout=30000

# MybatisProperties
#2.resourcees下创建mapper包
mybatis.mapper-locations=classpath:mapper/*.xml
#3.按路径创建entity包
mybatis.type-aliases-package=com.nowcoder.community.entity
mybatis.configuration.useGeneratedKeys=true
#header_url headerUrl这两种不同命名方式可以自动匹配
mybatis.configuration.mapUnderscoreToCamelCase=true

首先要写实体类，有个实体类能够封装表里的数据，然后才好用实体类对数据操作

有多少个字段就对应多少个属性，不过属性按照驼峰式命名的方式命名
Alt+insert生成get/set方法、toString方法（方便打印对象看数据）

要在dao数据访问层写UserMapper接口，声明增删改查的方法，再写上对应的配置文件（下一步）
加注解@Mapper
声明增删改查的方法

声明好Mapper之后，要想实现它，需要写一个配置文件，配置文件里给每个方法提供它所需要的sql，mybatis底层会自动生成实现类
在mapper包下创建user-mapper.xml文件

配置文件的所有格式在MyBatis官网都有说明
https://mybatis.org/mybatis-3/zh/getting-started.html

  
    select * from Blog where id = #{id}
  

注意：namespace写对应的Mapper的路径名+Mapper名，不然MyBatis也找不到对应的是谁呀
sql语句的格式（以select为例）官网都有，很详细

注意：sql语句里的属性名都是表格里的属性名，#{}里的属性名才是实体类里的属性名，不要搞混了

现在练习是一下子都写了，实际开发是用到什么方法再加

1.写注解

@RunWith(SpringRunner.class)
@SpringBootTest
@ContextConfiguration(classes = CommunityApplication.class)

2.注入Mapper
3.写测试类

3.5 调试着玩玩嘻嘻

Mybatis会自动实例化一个Mapper代理