使用数据传输对象避免写多表关联查询

@Service
public class QuestionServiceImpl implements QuestionService {
	@Autowired
	private QuestionMapper questionMapper;
	@Autowired
	private UserMapper userMapper;

    @Override
    public List<QuestionDTO> findAll() {
    	List<QuestionDTO> questionDTOs = new ArrayList<>();
    	List<Question> questions = questionMapper.findAll();
    
    	User user = null;
    	QuestionDTO questionDTO = null;
    	for (Question question : questions) {
    		user = userMapper.findById(question.getPublisher());
    
    		questionDTO = new QuestionDTO();
    		BeanUtils.copyProperties(question, questionDTO);
    
    		// 为数据传输对象设置user
    		questionDTO.setUser(user);
    		questionDTOs.add(questionDTO);
    	}
    
    	return questionDTOs;
    }
}

Question.java

@Data
public class Question {
	private Integer id;//
	private String title;// varchar(50)
	private String description;// text,
	private Long gmtCreated;// bigint(20) DEFAULT NULL,
	private Long gmtModified;//
	private Integer publisher;// 问题发布者id
	private Integer commentNum;// 评论数
	private Integer viewNum;// 浏览数
	private Integer likeNum;// 点赞数
	private String tag;// 问题标签
}

传输对象

package com.fei.dto;

import com.fei.domain.User;

import lombok.Data;

@Data
public class QuestionDTO {
	private Integer id;//
	private String title;// varchar(50)
	private String description;// text,
	private Long gmtCreated;// bigint(20) DEFAULT NULL,
	private Long gmtModified;//
	private Integer publisher;// 问题发布者id
	private Integer commentNum;// 评论数
	private Integer viewNum;// 浏览数
	private Integer likeNum;// 点赞数
	private String tag;// 问题标签
	
	// 数据传输对象，增加发布者User的id
	private User user;
}