mybatisplus 联表查询_工作中不推荐mybatisplus

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus-boot-starter</artifactId>
        <version>3.3.1.tmp</version>
    </dependency>
    
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>druid</artifactId>
        <version>1.2.8</version>
    </dependency>
    
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
        <version>1.18.4</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.6.4</version>
    </dependency>
</dependencies>

spring.datasource.password=数据库账号的登录密码
spring.datasource.username=数据库登录账号
spring.datasource.url=jdbc:mysql://localhost:3306/数据库名?useSSL=false&useUnicode=true&characterEncoding=utf-8&serverTimezone=GMT%2B8
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
server.port=8096
spring.application.name=MYBATISPLUSSERVER

@Data
@AllArgsConstructor
@NoArgsConstructor
@TableName("emp")  //告知mybatis-plus和数据库中的哪个表关联
public class User extends Model<User> implements Serializable {
    //主键id
    private int id;  //当实体类的属性名和和表中的列名相同，无需做任何设置

    @TableField("name") 
    private String userName; //属性名和列名不一致时设置映射，用userName属性和表中的name列进行关联

    private int age;
    private String email;
}

package com.qf.pro.dao;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.qf.pro.pojo.User;

public interface UserDao extends BaseMapper<User> {
    //BaseMapper<User> 默认封装了CRUD方法，通过泛型制定了所操作的实体类及表
}

package com.qf.mp2103.dao;

import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@MapperScan("com.qf.mp2103.dao")
public class MybatisPlusConfig {
    @Bean
    public PaginationInterceptor paginationInterceptor(){

        return new PaginationInterceptor();
    }
}

package com.qf.mp2103.service.impl;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.qf.mp2103.dao.UsersDao;
import com.qf.mp2103.pojo.Users;
import com.qf.mp2103.service.UsersService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

@Service
public class UserServiceImpl implements UsersService {
    @Autowired
    private UsersDao usersDao;
    
    @Override
    public List<Users> findUsers() {
        //mybatisplus 自动生成/提供的查询方法
        //由于是无条件查询，参数null
        return usersDao.selectList(null);
    }

    @Override
    public List<Users> findUsersByCondition(String name) {
        //创建QueryWrapper对象
        QueryWrapper<Users> wrapper=new QueryWrapper<Users>();
        //通过wrapper对象来设置查询条件
        //参数1：字段表名
        //参数2：所赋值
        //eq  等于
        wrapper.eq("name",name);

        return usersDao.selectList(wrapper);
    }

    @Override
    public List<Users> findUsersByCondition2(int startAge, int endAge) {
        QueryWrapper<Users> wrapper=new QueryWrapper<Users>();
        //年龄的范围
        wrapper.between("age",startAge,endAge);
        return usersDao.selectList(wrapper);
    }

    @Override
    public List<Users> findUsersByCondition3(Users users) {
        //多条件查询
        QueryWrapper<Users> wrapper=new QueryWrapper<Users>();
        //where name='' and age <=
//        wrapper.eq(true,"name",users.getUserName());
////        wrapper.le(true,"age",users.getAge());
        //where name='' or age >=
        wrapper.eq(true,"name",users.getUserName());
        wrapper.ge(false,"age",users.getAge());
        return usersDao.selectList(wrapper);
    }

    @Override
    public List<Users> findUsersByCondition4(Users users) {
        //模糊查询
        QueryWrapper<Users> wrapper=new QueryWrapper<Users>();
        //%关键字%
        wrapper.like("name",users.getUserName());
        //%明
        //wrapper.likeLeft()
        //李%
        //wrapper.likeRight();
        return usersDao.selectList(wrapper);
    }

    //排序查询
    @Override
    public List<Users> findUsers2() {
        QueryWrapper<Users> wrapper=new QueryWrapper<Users>();
        //设置排序条件
        wrapper.orderByDesc("id");

        return usersDao.selectList(wrapper);
    }

    @Override
    public List<Users> findUsersByPage(int page, int size) {
        //用于分页查询
        //select * from users  limit X,X
        QueryWrapper<Users> wrapper=new QueryWrapper<Users>();
        int start=(page-1)*size;
        //拼接
        wrapper.last("limit "+start+","+size);
        return usersDao.selectList(wrapper);
    }

    @Override
    public List<Users> findUsers3() {
        //查询指定列
        QueryWrapper<Users> wrapper=new QueryWrapper<Users>();
        //设置查询的列
        wrapper.select("id","email");

        return usersDao.selectList(wrapper);
    }

    @Override
    public boolean addUser(Users users) {
        //添加用户
        int result=usersDao.insert(users);
        return result==1;
    }

    @Override
    public boolean deleteUser(int id) {
        //删除用户--单个删除
        int result=usersDao.deleteById(id);
        //批量删除
        //usersDao.deleteBatchIds(List<Integer> list);
        return result==1;
    }

    @Override
    public boolean updateUser(Users users) {
        //要求表中的主键列是id的名字，使用id列作为条件
        int result=usersDao.updateById(users);
        //如果主键列的名字不是id,或者条件不是主键id
//        QueryWrapper<Users> wrapper=new QueryWrapper<Users>();
//        wrapper.eq("email",users.getEmail());
//        int result2=usersDao.update(users,wrapper);
        return result==1;
    }

    @Override
    public Users findUersById(int id) {
        //根据主键id查询单个对象
        return usersDao.selectById(id);
    }

    @Override
    public List<Users> findUsersByIds(List<Integer> list) {
        //根据id批量查询
        return usersDao.selectBatchIds(list);
    }

    @Override
    public Map<String,Object> findUsersByPage2(int page, int size) {
        //如果还有其他条件查询，声明条件构造器进行

        //创建分页插件对象
        //参数1：显示第几页数据
        //参数2：每页显示几条数据
        Page<Users> page1=new Page<Users>(page,size);
        //根据分页插件对象里的分页条件查询数据
        IPage<Users> iPage=usersDao.selectPage(page1,null);

        Map<String,Object> map=new HashMap<String, Object>();
        //总记录数  iPage.getTotal()
        map.put("totalCount",iPage.getTotal());
        //总页数 iPage.getPages()
        map.put("totalPage",iPage.getPages());
        //分页数据
        map.put("data",iPage.getRecords());
        return map;
    }

    @Override
    public List<Users> findUsers4(int age1, int age2, String email) {
        QueryWrapper<Users> queryWrapper=new QueryWrapper<Users>();
        queryWrapper.ge("age",age1).le("age",age2).or().likeRight("email",email);

        return usersDao.selectList(queryWrapper);
    }

    @Override
    public Users findUsers5(int id) {
        //创建实体类对象
        Users user=new Users();
        user.setId(id);
        //声明对象接收查询返回的结果
        Users getUser=user.selectById(id);
        return getUser;
    }

    @Override
    public void addUsers2(Users users) {
        //添加方法
        users.insert();
    }

    @Override
    public void updateUsers2(Users users) {
        //根据主键更新
        users.updateById();
    }

    @Override
    public void deleteUsers2(Users users) {
        //根据主键删除
        users.deleteById();
    }

    public Users findOne(String name){
        //根据其他条件查询单个数据，如果多于1条数据，则报异常
        //条件构造器
        QueryWrapper queryWrapper=new QueryWrapper();
        queryWrapper.eq("name",name);
        return usersDao.selectOne(queryWrapper);
    }
    //查询总记录数
    public int getUserCount(){
        //可以声明条件构造器
        return usersDao.selectCount(null);
    }

}