Java中使用MyBatis-Plus操作数据库的实例
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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: trueapplication-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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