Spring Boot+mybatis-plus之@Select注解

首先声明，此方式不推荐使用，不够灵活。推荐@Provider、xml映射文件方式。此文章仅仅是开发测试

1. 创建Spring Boot项目

• 通过IDEA创建，不过社区版没法直接创建。
• 通过https://start.spring.io/创建。

  • 选择对应project、language、Boot版本、group及包名、packaging、Java版本。右侧选择需要的依赖。

    
    
    图示
  • 选择“generate”下载后用ide工具打开即可。

2. pom.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.7.3</version>
    <relativePath/> <!-- lookup parent from repository -->
  </parent>
  <groupId>com.example</groupId>
  <artifactId>demo</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>demo</name>
  <description>Demo project for Spring Boot</description>
  <properties>
    <java.version>1.8</java.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-thymeleaf</artifactId>
    </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>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
    </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>
    </plugins>
  </build>

</project>

然后将mybatis-plus的依赖加入

<dependency>
  <groupId>com.baomidou</groupId>
  <artifactId>mybatis-plus-boot-starter</artifactId>
  <version>3.5.1</version>
</dependency>

3. application.properties文件中的配置项（端口、数据库配置、debug、mybatis）。

推荐将生成的application.properties删除，替换为application.yml，配置更简便。以下为yml文件配置

server:
  port: 8000
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/bank?useSSL=false&useUnicode=true&characterEncoding=utf-8&zeroDateTimeBehavior=convertToNull&transformedBitIsBoolean=true&serverTimezone=GMT%2B8&nullCatalogMeansCurrent=true&allowPublicKeyRetrieval=true
    username: root
    password: root
  thymeleaf:
    prefix: classpath:/templates/
    suffix: .html
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

4. 项目构造

   
   
   项目构造
5. 测试代码

• 最小功能实现
  • controller层：

package com.web.test.test.controller;
 
import com.web.test.test.service.TeacherService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class TeacherController {
    @Autowired
    private TeacherService teacherService;
　　
　　//Select By Id
    @RequestMapping("/showTeacher/{id}")
    public String selectTeacher(@PathVariable int id){
        return teacherService.selectTeacher(id).toString();
    }
     
    //Select All
    @RequestMapping("/selectAll")
    public String selectAll(){
        return teacherService.selectAll().toString();
    }

• 有的朋友想在return的时候直接跳转界面去，看到@RestController了吗，这个是ResponseBody和Controller的集合，意思是return的数据都变成json的格式，返回到前端，不会跳转界面。如果想跳转页面的话，就需要把RestController改成Controller，就会跳转页面了。
• 还有些朋友想带着数据返回到重新定义的页面去，对于这种需求，我建议使用“视图解释器解析”——ModelAndVIew。ModelAndView的用法类似于这样：

@RequestMapping
public ModelAndView list(Model model) {
    model.addAttribute("userList", userRepository.listUsers());
    model.addAttribute("title", "用户管理");
        // new ModelAndView(目标页面的路径, 目标页面接到的返回值名称, api封装好返回的数据)
    return new ModelAndView("users/list","userModel",model);
}

• Service层：

package com.we b.test.test.service;
 
import com.web.test.test.domain.Teacher;
import java.util.List;
 
public interface TeacherService {
    Teacher selectTeacher(int id);
    List<Teacher> selectAll();
}

• Service实现类

package com.test.test.Service.impl;
 
import com.test.test.Service.TeacherService;
import com.test.test.domain.Teacher;
import com.test.test.mapper.TeacherMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
 
import java.util.List;
 
@Service
public class TeacherImpl implements TeacherService {
 
    @Autowired
    TeacherMapper mapper;
 
    @Override
    public Teacher selectTeacher(int id) {
        return mapper.selectTeacher(id);
    }
 
    @Override
    public List<Teacher> selectAll() {
        return mapper.selectAll();
    }
}

• Mapper层
  • 只需要继承BaseMapper即可

public interface UserMapper extends BaseMapper<User> {

    @Select("select * from user a inner join user_test b on a.id = b.user_id where a.name = '王' and b.is_deleted = 0")
    List<User> userList();
}