MyBatis-Plus 查询指定字段的实现

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.kaven</groupId>
  <artifactId>mybatis-plus</artifactId>
  <version>1.0-SNAPSHOT</version>

  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.4.RELEASE</version>
    <relativePath/>
  </parent>

  <properties>
    <java.version>1.8</java.version>
  </properties>

  <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>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-webflux</artifactId>
    </dependency>
    <dependency>
      <groupId>com.baomidou</groupId>
      <artifactId>mybatis-plus-boot-starter</artifactId>
      <version>3.4.0</version>
    </dependency>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.49</version>
    </dependency>
    <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
    </plugins>
  </build>
</project>

spring:
 application:
  name: mybatis-plus
 datasource:
  driver-class-name: com.mysql.jdbc.Driver
  username: root
  password: ITkaven@123
  url: jdbc:mysql://127.0.0.1:3306/test?characterEncoding=utf-8&useSSL=false

server:
 port: 8085

logging:
 level:
  root: warn
  com.kaven.mybatisplus.dao: trace
 pattern:
  console: '%p%m%n'

mybatis-plus:
 mapper-locations: classpath:mappers/*.xml

package com.kaven.mybatisplus.entity;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

@TableName("user")
@Data
public class User {

  @TableId
  private String id;

  @TableField("username")
  private String username;

  @TableField("password")
  private String password;

  @TableField("age")
  private Integer age;

  /**
   * 使用 @TableField(exist = false) ，表示该字段在数据库中不存在 ，所以不会插入数据库中
   * 使用 transient 、 static 修饰属性也不会插入数据库中
   */
  @TableField(exist = false)
  private String phone;
}

package com.kaven.mybatisplus.dao;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.kaven.mybatisplus.entity.User;
import org.springframework.stereotype.Component;


@Component
public interface UserMapper extends BaseMapper<User> {}

package com.kaven.mybatisplus;

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

@SpringBootApplication
@MapperScan(basePackages = "com.kaven.mybatisplus.dao")
public class AppRun {
  public static void main(String[] args) {
    SpringApplication.run(AppRun.class , args);
  }
}

package com.kaven.mybatisplus.dao;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.kaven.mybatisplus.entity.User;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;
import java.util.List;


@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

  @Autowired
  private UserMapper userMapper;

  @Test
  public void selectList(){
    QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
//    QueryWrapper<User> userQueryWrapper = Wrappers.query(); 和上面一样的效果
    userQueryWrapper.select("username", "age").like("username" , "k").lt("age" , 35);
//    userQueryWrapper.like("username" , "k").lt("age" , 35).select("username", "age"); 
//    把select()放在最后面也可以，但我一般喜欢放在最前面，和sql语法保持一致
    List<User> userList = userMapper.selectList(userQueryWrapper);
    userList.forEach(System.out::println);
  }
}

package com.kaven.mybatisplus.dao;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.kaven.mybatisplus.entity.User;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;
import java.util.List;


@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

  @Autowired
  private UserMapper userMapper;

  @Test
  public void selectList2(){
    QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
//    QueryWrapper<User> userQueryWrapper = Wrappers.query(); 和上面一样的效果
    userQueryWrapper.select(User.class , e->!e.getColumn().equals("password")).like("username" , "k")
        .between("age" , 25 , 35)
        .isNotNull("password");
    List<User> userList = userMapper.selectList(userQueryWrapper);
    userList.forEach(System.out::println);
  }
}