Mybatis Plus的基础使用

  • 为简化开发而生

1.实体类的定义

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@Data
@TableName("userswork")  // 映射表
public class Userwork {
  @TableId(type = IdType.AUTO)  // 主键策略
  private int id;
  private int workid;
  private int userid;
  
  @TableField(exist = false) // 列策略：是否对应表属性，查询时是否返回结果....
  private int other;
}

2.Mapper的书写（多表查询使用SQL拼接）

  • 继承BaseMapper实现基本的CURD功能
  • 简单语句可以使用自带的CRUD
  • 复杂语句也可以使用sql语句拼接
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package kid1999.upload.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import kid1999.upload.model.HomeWork;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;
import java.util.List;

@Mapper
public interface homeworkMapper extends BaseMapper<HomeWork> {

    @Select("select * from homework where title = #{title} and id in (select workid from userswork where userid = #{userId})")
    HomeWork findHKByTitleAndUserID(String title,int userId);

    @Insert("insert into homework(title, infomation, createtime, endtime, type, addr) values (#{title},#{infomation} ,#{createtime} ,#{endtime} ,#{type} ,#{addr} )")
    void addHomeWork(HomeWork homeWork);

    @Select("select * from homework where id in (select workid from userswork where userid = #{userid} ) ")
    List<HomeWork> findByUserId(Integer userid);
    
    @Select("select addr from homework where id = (select workid from student where student.id = #{uid})")
    String findaddrBySid(int uid);
    
    
    @Select("select * from homework where title = #{title} and id in (select workid from userwork where userid = #{userId})")
    HomeWork findHKByTitle(String title,int userId);
}

3.在Service中实现一些简单的单表CRUD

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package kid1999.upload.service;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import kid1999.upload.mapper.userMapper;
import kid1999.upload.model.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;



@Service
public class userService {

  @Autowired
  private userMapper userMapper;

  // 简单查询使用 QueryWrapper 
  public User findUserByName(String name) {
    QueryWrapper wrapper = new QueryWrapper();
    wrapper.eq("name",name);
    return userMapper.selectOne(wrapper);
  }

  // 增加 使用自带的 insert
  public int addUser(User user) {
    return userMapper.insert(user);
  }

  public User login(User user) {
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.eq("name",user.getName())
            .eq("password",user.getPassword());
    return userMapper.selectOne(wrapper);
  }
  
  // 更新student
  public int updateStudent(Student student) {
	QueryWrapper<Student> wrapper = new QueryWrapper<>();
	wrapper.eq("id",student.getId())
			.eq("name",student.getName());
	return studentMapper.update(student,wrapper);
  }
}

后续再修订 。。。。