Java中使用MyBatis-Plus操作数据库的实例

MyBatis-Plus

MyBatis-Plus (opens new window)（简称 MP）是一个 MyBatis (opens new window)的增强工具，在 MyBatis 的基础上只做增强不做改变，为简化开发、提高效率而生。

MyBatis可以直接在xml中通过SQL语句操作数据库，很灵活。但其操作都要通过SQL语句进行，就必须写大量的xml文件，很麻烦。mybatis-plus就很好的解决了这个问题。

官网

MyBatis-Plus 官方文档

使用

        这里我用的数据库是mysql8，新建test数据库，并创建user表

     建表语句

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
 
-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user`  (
  `id` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '主键',
  `name` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '姓名',
  `age` int(0) NULL DEFAULT NULL COMMENT '年龄',
  `address` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '地址',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
 
SET FOREIGN_KEY_CHECKS = 1;

  引入依赖

        这里我用的数据库是mysql8

     <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.3</version>
        <relativePath/>
    </parent>
 
    <dependencies>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-test</artifactId>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.1</version>
        </dependency>
        <!--Druid连接池-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.9</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.25</version>
        </dependency>
    </dependencies>

分别创建application.yml及application-dev.yml文件

 application.yml

# Spring配置
spring:
  # 环境设置
  profiles:
    active: dev
  # 模板引擎
  thymeleaf:
    mode: HTML
    encoding: utf-8
    # 禁用缓存
    cache: false
  # 服务模块
  devtools:
    restart:
      # 热部署开关
      enabled: true

application-dev.yml

# 开发环境配置
server:
  # 服务器的HTTP端口，默认为80
  port: 8081
 
spring:
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.mysql.cj.jdbc.Driver
    druid:
      url: jdbc:mysql://localhost:3307/test?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&useSSL=true&serverTimezone=GMT%2B8
      username: root
      password: 123456
      initial-size: 5
      min-idle: 10
      max-active: 20
      max-wait: 60000
      time-between-eviction-runs-millis: 60000
      min-evictable-idle-time-millis: 300000
      validation-query: select 'x'
      test-while-idle: true
      test-on-borrow: false
      test-on-return: false
      pool-prepared-statements: true
      max-open-prepared-statements: 50
      max-pool-prepared-statement-per-connection-size: 20

编写实体类User.java,这里用到lombok

@Data
public class User {
    private String id;
    private String name;
    private Integer age;
    private String address;
}

创建mapper文件夹,并编写 Mapper 类 UserMapper.java

public interface UserMapper extends BaseMapper<User> {
 
}

在 Spring Boot 启动类中添加 @MapperScan 注解，扫描 Mapper 文件夹：

@SpringBootApplication
@MapperScan("com.mybatisplus.mapper")
public class MainApplication {
    public static void main(String[] args)
    {
        SpringApplication.run(MainApplication.class, args);
    }
}

添加测试类，进行功能测试：

测试数据插入数据库

    @Autowired
    private UserMapper userMapper;
 
    @Test
    public void testInsert() {
        System.out.println(("----- insert method test ------"));
        User user = new User();
        // 自动生成主键,例如550E8400-E29B-11D4-A716-446655440000
        String id = UUID.randomUUID().toString();
        String replaceAll = id.replaceAll("-", "");
        //550E8400E29B11D4A716446655440000
        user.setId(replaceAll);
        user.setName("张三");
        user.setAge(21);
        user.setAddress("北京市海淀区");
        int insert = userMapper.insert(user);
        if(insert>0){
            System.out.println("插入成功："+user);
        }else{
            System.out.println("插入失败！");
        }
    }

 测试查询所有

    @Autowired
    private UserMapper userMapper;   
     
    @Test
    public void testSelect() {
        System.out.println(("----- selectAll method test ------"));
        List<User> userList = userMapper.selectList(null);
        userList.forEach(System.out::println);
    }

 测试删除数据

        删除姓名等于“张三”的记录

    @Autowired
    private UserMapper userMapper;
    
    @Test
    public void testDelete() {
        System.out.println(("----- delete method test ------"));
        LambdaQueryWrapper<User> wrapper = new LambdaQueryWrapper<>();
        User user = new User();
        user.setName("张三");
        wrapper.eq(User::getName, user.getName());
        int delete = userMapper.delete(wrapper);
        if(delete>0){
            System.out.println("删除成功："+user);
        }else{
            System.out.println("删除失败！");
        }
    }

 测试修改数据

 修改前先执行下插入

        修改还可以用userMapper.updateById(T entity)方法来修改，传入一个实体类

    @Autowired
    private UserMapper userMapper;
    
    @Test
    public void testUpdate() {
        System.out.println(("----- update method test ------"));
        LambdaQueryWrapper<User> wrapper = new LambdaQueryWrapper<>();
        User user = new User();
        user.setName("张三");
        wrapper.eq(User::getName, user.getName());
        User userNew = new User();
        userNew.setName("李四");
        int update = userMapper.update(userNew, wrapper);
        if(update>0){
            System.out.println("修改成功："+user);
        }else{
            System.out.println("修改失败！");
        }
    }

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