mybatis plus 项目模板

前言

• ​​案例地址​​

项目搭建

• 新建1个spring boot项目，导入所需依赖

点击查看详情

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </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-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-devtools</artifactId>
        <scope>runtime</scope>
        <optional>true</optional>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
    </dependency>
    <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus-boot-starter</artifactId>
        <version>3.4.3.1</version>
    </dependency>
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>druid</artifactId>
        <version>1.2.6</version>
    </dependency>
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>fastjson</artifactId>
        <version>1.2.73</version>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <configuration>
                <excludes>
                    <exclude>
                        <groupId>org.projectlombok</groupId>
                        <artifactId>lombok</artifactId>
                    </exclude>
                </excludes>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-resources-plugin</artifactId>
            <version>3.1.0</version>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>2.22.1</version>
            <configuration>
                <skipTests>true</skipTests>
            </configuration>
        </plugin>
    </plugins>
</build>

• 编写yml

点击查看详情

# 端口号
server:
  port: 8080

spring:
  application:
    name: mybatisdemo
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://192.168.0.102:3306/mybatisdemo?characterEncoding=utf-8&serverTimezone=UTC
    username: root
    password: 123456
  mvc:
    view:
      suffix: ".html"

# 开启驼峰命名自动映射
mybatis:
  configuration:
    map-underscore-to-camel-case: true
  mapperLocations: classpath:mapper/*.xml    # 映射xml文件

logging:
  level:
    com:
      chnq:
        mybatisdomo: debug

• 启动类添加注解​​@MapperScan​​

点击查看详情

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan("com.chnq.mybatisdemo.mapper")
public class MybatisDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(MybatisDemoApplication.class, args);
    }

}

• 创建数据库



• 
  



• 编写配置类​​MybatisPlusConfig​​

点击查看详情

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.annotation.EnableTransactionManagement;

@EnableTransactionManagement
@Configuration
@MapperScan("com.chnq.mybatisdemo.mapper")
public class MybatisPlusConfig {

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }

}

• 编写实体类User

点击查看详情

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
import lombok.experimental.Accessors;
import java.io.Serializable;
import java.util.Date;

@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
@Accessors(chain = true)
@TableName("t_user")
public class User implements Serializable {
    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;
    private String username;
    private String password;
    private Date birthday;

}

• 编写实体类Book

点击查看详情

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
import lombok.experimental.Accessors;
import java.io.Serializable;
import java.math.BigDecimal;

@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
@Accessors(chain = true)
@TableName("t_book")
public class Book implements Serializable {
    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;
    private String bookname;
    private BigDecimal price;   // 保留小数点后两位
    private String author;

}

mybatis plus 环境搭建

• mapper

点击查看详情

@Mapper
public interface UserMapper extends BaseMapper<User> {

}

• service

点击查看详情

public interface UserService extends IService<User> {

}

// 实现类
@Service
@Transactional
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {

    @Resource
    private UserMapper userMapper;

}

• 控制器

点击查看详情

@Controller
public class UserController {
    @Resource
    UserService userService;

    @Resource
    UserMapper userMapper;

    // 调用service层接口查询所有
    @GetMapping("/getUsers")
    @ResponseBody
    public String getUserList(){
        List<User> user = userService.list();
        System.out.println(user);
        return RespResult.success("获取成功！", user);
    }

    // 调用mapper层接口查询所有
    @GetMapping("/getUsers2")
    @ResponseBody
    public String getUserTest(){
        List<User> users = userMapper.selectList(null);
        users.forEach(user-> System.out.println("user = " + user));
        return RespResult.success("获取成功！", users);
    }

    // 调用mapper层接口查询单个
    @GetMapping("/getUser")
    @ResponseBody
    public String testFindOne(@PathParam("id") int id){
        User user = userMapper.selectById(id);
        return RespResult.success("获取成功！", user);
    }

    // 调用mapper层接口添加数据
    @GetMapping("/save")
    @ResponseBody
    public String testSave(){
        User user = new User();
        user.setUsername("小兰");
        user.setPassword("123456");
        userMapper.insert(user);
        return RespResult.success("添加成功！", user);
    }

}

• 测试一下

点击查看详情

• 在控制器中注入了service对象和mapper对象，就可以直接调用mybatis plus为我们提供的方法，​​ctrl + f12​​可查看方法



• 
  



• 更过crud方法参考​​mybatis puls官网​​
• ​​使用注解自定义sql​​​ ​​参考​​

点击查看详情

// mapper层
@Mapper
public interface UserMapper extends BaseMapper<User> {

    // 使用注解自定义sql
    @Select("select * from t_user")
    List<User> getAll();

}

// 控制层
@Controller
public class UserController {

    @Resource
    UserMapper userMapper;

    // 使用注解自定义sql
    @GetMapping("/getAll")
    @ResponseBody
    public String getAll(){
        List<User> users = userMapper.getAll();
        System.out.println(users);
        return RespResult.success("添加成功！", users);
    }

}

• ​​使用xml自定义sql​​​​参考​​

点击查看详情

// mapper
@Mapper
public interface BookMapper extends BaseMapper<Book> {

    List<Book> getAll();

}

// xml，在resource路径下新建mapper文件夹，在该文件夹下编写xml文件
<?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" >

<mapper namespace="com.chnq.mybatisdemo.mapper.BookMapper">

    <select id="getAll" resultType="com.chnq.mybatisdemo.model.Book">
        select id, bookname, price, author from t_book
    </select>

</mapper>

// service
public interface BookService extends IService<Book> {

    List<Book> getAll();

}

// 实现类
@Service
@Transactional
public class BookServiceImpl extends ServiceImpl<BookMapper, Book> implements BookService {

    @Resource
    private BookMapper bookMapper;

    @Override
    public List<Book> getAll() {
        return bookMapper.getAll();
    }

}

// controller
@RestController
@RequestMapping(value = {"/book"})
public class BookController {
    @Resource
    BookService bookService;

    @RequestMapping(value = {"/getBooks"})
    @ResponseBody
    public String decrease() {
        List<Book> books = new LinkedList<>();
        books = bookService.getAll();
        System.out.println(books);
        return RespResult.success(books);
    }

}

• ​​使用匿名内部类风格构造器自定义sql​​​​参考​​

点击查看详情

// mapper层
@Mapper
public interface UserMapper extends BaseMapper<User> {

    @UpdateProvider(type = UserProvider.class, method = "updateUser")
    int updateUser(@Param("user") User user, @Param("id") int id);

    class UserProvider {
        public String updateUser(@Param("user") User user, @Param("id") int id) {
            SQL sql = new SQL();
            sql.UPDATE("t_user");
            if(user.getUsername() != null) {
                sql.SET("username=#{user.username}");
            }
            if(user.getPassword() != null) {
                sql.SET("password = #{user.password}");
            }
            if(user.getBirthday() != null) {
                sql.SET("birthday = #{user.birthday}");
            }
            sql.WHERE("id = #{id}");
            return sql.toString();
        }
    }

}

// controller层
@Controller
public class UserController {

    @Resource
    UserMapper userMapper;

    @GetMapping("/testUpdate")
    @ResponseBody
    public String testUpdate(@PathParam("id") int id){
        User user = new User();
        user.setUsername("cyq");
        user.setPassword("123456");
        userMapper.updateUser(user, id);
        return RespResult.success("添加成功！", user);
    }

}

• ​​使用Fluent风格自定义sql​​​​参考​​

点击查看详情

// mapper层
@Mapper
public interface UserMapper extends BaseMapper<User> {

    @SelectProvider(type = addUserProvider.class, method = "addUser")
    Integer addUser(@Param("username") String username, @Param("password") String password, @Param("birthday") Date birthday);

    class addUserProvider {
        public String addUser(@Param("username") String username, @Param("password") String password, @Param("birthday") Date birthday) {
            String sql = new SQL()
                    .INSERT_INTO("t_user")
                    .VALUES("username, password", "#{username}, #{password}")
                    .VALUES("birthday", "#{birthday}")
                    .toString();
            return sql;
        }
    }

}

// controller层
@Controller
public class UserController {

    @Resource
    UserMapper userMapper;

    @GetMapping("/testAdd")
    @ResponseBody
    public String testAdd(){
        Date bir = new Date();
        userMapper.addUser("chenx", "123456", bir);
        return RespResult.success("添加成功！");
    }

}

报错

• 错误描述：拉取依赖时报错​​Cannot find file​​
• 错误原因：maven3.8.2的问题，切换为idea自带maven或安装maven3.6.1及其以下版本
• ​​参考​​
• 错误2：在控制层中调用mapper层的insert方法插入数据时报错：​​java.lang.IllegalArgumentException: argument type mismatch​​
• 错误原因：实体类中属性的类型与数据库中字段类型不一致、实体类没有构造方法、MybatisPlus主键生成策略不匹配
• ​​参考​​
• 应该将实体类修改为如下

@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
@Accessors(chain = true)
@TableName("t_user")
public class User implements Serializable {
    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;
    private String username;
    private String password;
    private Date birthday;

}

• 使用Fluent风格自定义sql时报错：​​attempted to return null from a method with a primitive return type (int)​​
• 解决方案：将mapper层的返回类型int改为Integer
• ​​参考​​