MyBatis-Plus查询排除大字段的性能优化指南

CREATE TABLE article
(
    id                  BIGINT AUTO_INCREMENT PRIMARY KEY COMMENT '主键ID',
    title               VARCHAR(200)   NOT NULL COMMENT '文章标题',
    summary             VARCHAR(500)   NULL COMMENT '摘要',
    content             LONGTEXT       NULL COMMENT '文章正文(富文本)',
    extra_config        TEXT           NULL COMMENT '扩展配置(JSON)',
    cover_image_base64  MEDIUMTEXT     NULL COMMENT '封面图Base64',
    category_id         BIGINT         NOT NULL COMMENT '分类ID',
    author              VARCHAR(64)    NULL COMMENT '作者',
    view_count          INT            DEFAULT 0 COMMENT '阅读量',
    status              TINYINT        DEFAULT 0 COMMENT '状态 0-草稿 1-已发布 2-已下架',
    publish_time        DATETIME       NULL COMMENT '发布时间',
    create_by           VARCHAR(64)    NULL COMMENT '创建者',
    create_time         DATETIME       DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    update_by           VARCHAR(64)    NULL COMMENT '更新者',
    update_time         DATETIME       DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
    del_flag            TINYINT        DEFAULT 0 NOT NULL COMMENT '删除标识 0-正常 1-已删除'
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='文章表';

id, title, summary, category_id, author, view_count, status, publish_time

.select(EntityClass.class, predicate)

.select("id", "title", "summary", "status")

.select(Article::getId, Article::getTitle, Article::getSummary)

package com.example.article.entity;

import com.baomidou.mybatisplus.annotation.*;
import lombok.Data;
import java.time.LocalDateTime;

/**
 * 文章实体
 *
 * @author zhangsan
 */
@Data
@TableName("article")
public class Article {

    @TableId(type = IdType.AUTO)
    private Long id;

    /** 文章标题 */
    private String title;

    /** 摘要 */
    private String summary;

    /** 文章正文(富文本) —— LONGTEXT 大字段 */
    private String content;

    /** 扩展配置(JSON) —— TEXT 大字段 */
    private String extraConfig;

    /** 封面图Base64 —— MEDIUMTEXT 大字段 */
    private String coverImageBase64;

    /** 分类ID */
    private Long categoryId;

    /** 作者 */
    private String author;

    /** 阅读量 */
    private Integer viewCount;

    /** 状态 0-草稿 1-已发布 2-已下架 */
    private Integer status;

    /** 发布时间 */
    private LocalDateTime publishTime;

    /** 创建者 */
    private String createBy;

    /** 创建时间 */
    private LocalDateTime createTime;

    /** 更新者 */
    private String updateBy;

    /** 更新时间 */
    private LocalDateTime updateTime;

    /** 逻辑删除标识 */
    @TableLogic
    private Integer delFlag;
}

package com.example.article.vo;

import lombok.Data;
import java.time.LocalDateTime;

/**
 * 文章列表 VO —— 不包含 content、extraConfig、coverImageBase64
 *
 * @author zhangsan
 */
@Data
public class ArticleListVo {

    private Long id;

    /** 文章标题 */
    private String title;

    /** 摘要 */
    private String summary;

    /** 分类ID */
    private Long categoryId;

    /** 作者 */
    private String author;

    /** 阅读量 */
    private Integer viewCount;

    /** 状态 */
    private Integer status;

    /** 发布时间 */
    private LocalDateTime publishTime;

    /** 创建时间 */
    private LocalDateTime createTime;
}

package com.example.article.vo;

import lombok.Data;
import java.time.LocalDateTime;

/**
 * 文章详情 VO —— 包含全部字段
 *
 * @author zhangsan
 */
@Data
public class ArticleDetailVo {

    private Long id;
    private String title;
    private String summary;
    private String content;
    private String extraConfig;
    private String coverImageBase64;
    private Long categoryId;
    private String author;
    private Integer viewCount;
    private Integer status;
    private LocalDateTime publishTime;
    private LocalDateTime createTime;
    private LocalDateTime updateTime;
}

package com.example.article.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.article.entity.Article;
import com.example.article.vo.ArticleListVo;
import org.apache.ibatis.annotations.Mapper;

/**
 * 文章 Mapper
 *
 * @author zhangsan
 */
@Mapper
public interface ArticleMapper extends BaseMapper<Article> {

    // 如果使用 MyBatis-Plus 扩展的 BaseMapperPlus，可支持 selectVoList
    // 此处以原生 BaseMapper 为基础，Service 层做转换
}

package com.example.article.service.impl;

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.toolkit.Wrappers;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.example.article.entity.Article;
import com.example.article.mapper.ArticleMapper;
import com.example.article.service.ArticleService;
import com.example.article.vo.ArticleListVo;
import com.example.article.vo.ArticleDetailVo;
import lombok.RequiredArgsConstructor;
import org.springframework.beans.BeanUtils;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.stream.Collectors;

/**
 * 文章 Service 实现
 *
 * @author zhangsan
 */
@Service
@RequiredArgsConstructor
public class ArticleServiceImpl implements ArticleService {

    private final ArticleMapper articleMapper;

    /**
     * 查询已发布文章列表（排除大字段）
     * <p>
     * 列表页只需要标题、摘要、作者等轻量信息，
     * 不需要 content、extraConfig、coverImageBase64 三个大字段。
     *
     * @param categoryId 分类ID（可选）
     * @return 文章列表
     */
    @Override
    public List<ArticleListVo> listPublishedArticles(Long categoryId) {
        LambdaQueryWrapper<Article> wrapper = Wrappers.<Article>lambdaQuery()
                // ★ 核心：排除三个大字段
                .select(Article.class, field ->
                        !"content".equals(field.getProperty())
                        && !"extraConfig".equals(field.getProperty())
                        && !"coverImageBase64".equals(field.getProperty())
                )
                .eq(Article::getStatus, 1)
                .eq(Article::getDelFlag, 0)
                .eq(categoryId != null, Article::getCategoryId, categoryId)
                .orderByDesc(Article::getPublishTime);

        List<Article> articles = articleMapper.selectList(wrapper);

        // 转换为 VO
        return articles.stream().map(article -> {
            ArticleListVo vo = new ArticleListVo();
            BeanUtils.copyProperties(article, vo);
            return vo;
        }).collect(Collectors.toList());
    }

    /**
     * 分页查询已发布文章（排除大字段）
     *
     * @param pageNum    页码
     * @param pageSize   每页条数
     * @param categoryId 分类ID（可选）
     * @return 分页结果
     */
    @Override
    public Page<ArticleListVo> pagePublishedArticles(int pageNum, int pageSize, Long categoryId) {
        LambdaQueryWrapper<Article> wrapper = Wrappers.<Article>lambdaQuery()
                // ★ 同样排除大字段
                .select(Article.class, field ->
                        !"content".equals(field.getProperty())
                        && !"extraConfig".equals(field.getProperty())
                        && !"coverImageBase64".equals(field.getProperty())
                )
                .eq(Article::getStatus, 1)
                .eq(Article::getDelFlag, 0)
                .eq(categoryId != null, Article::getCategoryId, categoryId)
                .orderByDesc(Article::getPublishTime);

        Page<Article> page = articleMapper.selectPage(new Page<>(pageNum, pageSize), wrapper);

        // 转换为 VO 分页
        Page<ArticleListVo> voPage = new Page<>(page.getCurrent(), page.getSize(), page.getTotal());
        List<ArticleListVo> voList = page.getRecords().stream().map(article -> {
            ArticleListVo vo = new ArticleListVo();
            BeanUtils.copyProperties(article, vo);
            return vo;
        }).collect(Collectors.toList());
        voPage.setRecords(voList);
        return voPage;
    }

    /**
     * 查询文章详情（包含全部字段）
     * <p>
     * 详情页需要展示正文、配置等完整信息，不做字段过滤。
     *
     * @param id 文章ID
     * @return 文章详情
     */
    @Override
    public ArticleDetailVo getArticleDetail(Long id) {
        Article article = articleMapper.selectOne(
                Wrappers.<Article>lambdaQuery()
                        .eq(Article::getId, id)
                        .eq(Article::getDelFlag, 0)
        );
        if (article == null) {
            return null;
        }
        ArticleDetailVo vo = new ArticleDetailVo();
        BeanUtils.copyProperties(article, vo);
        return vo;
    }

    /**
     * 下拉选择器：只查 id 和 title（极端精简场景）
     *
     * @return 文章简要列表
     */
    @Override
    public List<ArticleListVo> listArticleOptions() {
        LambdaQueryWrapper<Article> wrapper = Wrappers.<Article>lambdaQuery()
                // 只需要两个字段，用 Lambda 方式更直观
                .select(Article::getId, Article::getTitle)
                .eq(Article::getStatus, 1)
                .eq(Article::getDelFlag, 0)
                .orderByDesc(Article::getPublishTime);

        List<Article> articles = articleMapper.selectList(wrapper);
        return articles.stream().map(article -> {
            ArticleListVo vo = new ArticleListVo();
            vo.setId(article.getId());
            vo.setTitle(article.getTitle());
            return vo;
        }).collect(Collectors.toList());
    }
}

SELECT id, title, summary, category_id, author, view_count, status,
       publish_time, create_by, create_time, update_by, update_time, del_flag
FROM article
WHERE status = 1
  AND del_flag = 0
  AND category_id = ?
ORDER BY publish_time DESC

SELECT id, title, summary, content, extra_config, cover_image_base64,
       category_id, author, view_count, status, publish_time,
       create_by, create_time, update_by, update_time, del_flag
FROM article
WHERE status = 1
  AND del_flag = 0
ORDER BY publish_time DESC

.select(Article.class, field -> !"content".equals(field.getProperty()))

// 显式列出需要的列（数据库列名，下划线风格）
.select("id", "title", "summary", "category_id", "author",
        "view_count", "status", "publish_time", "create_time")

// Lambda 方法引用，类型安全
.select(Article::getId, Article::getTitle, Article::getSummary,
        Article::getCategoryId, Article::getAuthor,
        Article::getViewCount, Article::getStatus,
        Article::getPublishTime, Article::getCreateTime)

// 方式 A：按 Java 属性名匹配
.select(Article.class, field -> !"extraConfig".equals(field.getProperty()))

// 方式 B：按数据库列名匹配
.select(Article.class, field -> !"extra_config".equals(field.getColumn()))

// 初始：字段名与列名一致
private String extraConfig;  // → 数据库列 extra_config

// 后来：加了 @TableField 自定义列名
@TableField("ext_cfg")
private String extraConfig;  // → 数据库列变为 ext_cfg

.select(Article.class, field ->
        !"content".equals(field.getProperty())
        && !"coverImageBase64".equals(field.getProperty())
)

.select(Article::getId, Article::getTitle)

String[] columns = buildColumnsDynamically();
wrapper.select(columns);

<select id="selectArticleWithCategory" resultType="com.example.article.vo.ArticleListVo">
    SELECT a.id, a.title, a.summary, a.author, a.view_count,
           a.status, a.publish_time, a.create_time,
           c.name AS categoryName
    FROM article a
    LEFT JOIN category c ON a.category_id = c.id
    WHERE a.status = 1
      AND a.del_flag = 0
      AND c.del_flag = 0
    ORDER BY a.publish_time DESC
</select>

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

-- 优化后
EXPLAIN SELECT id, title, summary, category_id, author, view_count, status, publish_time
FROM article
WHERE status = 1 AND del_flag = 0
ORDER BY publish_time DESC;
-- 优化前（对比）
EXPLAIN SELECT *
FROM article
WHERE status = 1 AND del_flag = 0
ORDER BY publish_time DESC;

// 在测试环境中对比
long start = System.nanoTime();
List<Article> fullList = articleMapper.selectList(
    Wrappers.<Article>lambdaQuery().eq(Article::getStatus, 1));
long fullCost = System.nanoTime() - start;

start = System.nanoTime();
List<Article> lightList = articleMapper.selectList(
    Wrappers.<Article>lambdaQuery()
        .select(Article.class, f -> !"content".equals(f.getProperty())
                && !"extraConfig".equals(f.getProperty())
                && !"coverImageBase64".equals(f.getProperty()))
        .eq(Article::getStatus, 1));
long lightCost = System.nanoTime() - start;

log.info("全字段查询: {}ms, 排除大字段: {}ms, 提升: {}%",
    fullCost / 1_000_000,
    lightCost / 1_000_000,
    (fullCost - lightCost) * 100 / fullCost);

-- 针对列表查询的联合索引
CREATE INDEX idx_article_list
    ON article(status, del_flag, category_id, publish_time DESC);

-- 极端精简查询，可被索引完全覆盖
SELECT id, title FROM article WHERE status = 1 AND del_flag = 0;

-- 主表：高频访问的轻量字段
CREATE TABLE article (
    id            BIGINT AUTO_INCREMENT PRIMARY KEY,
    title         VARCHAR(200) NOT NULL,
    summary       VARCHAR(500),
    category_id   BIGINT NOT NULL,
    author        VARCHAR(64),
    view_count    INT DEFAULT 0,
    status        TINYINT DEFAULT 0,
    publish_time  DATETIME,
    create_time   DATETIME DEFAULT CURRENT_TIMESTAMP,
    update_time   DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    del_flag      TINYINT DEFAULT 0 NOT NULL
) COMMENT='文章主表';
-- 内容表：低频访问的大字段
CREATE TABLE article_content (
    article_id         BIGINT PRIMARY KEY COMMENT '关联文章ID',
    content            LONGTEXT COMMENT '文章正文',
    extra_config       TEXT COMMENT '扩展配置',
    cover_image_base64 MEDIUMTEXT COMMENT '封面图',
    CONSTRAINT fk_article_content FOREIGN KEY (article_id) REFERENCES article(id)
) COMMENT='文章内容表';

@Cacheable(value = "article:published:list", key = "#categoryId", unless = "#result.isEmpty()")
public List<ArticleListVo> listPublishedArticles(Long categoryId) {
    // 查询逻辑...
}

// 第一步：列表查询（无大字段）
List<ArticleListVo> list = listPublishedArticles(categoryId);

// 第二步：用户点击某篇文章时，再查详情（含大字段）
ArticleDetailVo detail = getArticleDetail(clickedId);

// ❌ 错误认知
// "ArticleListVo 里没有 content 字段，所以 MyBatis-Plus 不会查 content"
List<Article> list = articleMapper.selectList(
    Wrappers.<Article>lambdaQuery().eq(Article::getStatus, 1)
);

// ❌ 错误：getColumn() 返回数据库列名（下划线风格），不是 Java 属性名
.select(Article.class, field -> !"extraConfig".equals(field.getColumn()))

// ✅ 用 getProperty() 匹配 Java 属性名
.select(Article.class, field -> !"extraConfig".equals(field.getProperty()))

// ✅ 或用 getColumn() 匹配数据库列名
.select(Article.class, field -> !"extra_config".equals(field.getColumn()))

// ❌ 分页 + 全字段
Page<Article> page = articleMapper.selectPage(
    new Page<>(1, 20),
    Wrappers.<Article>lambdaQuery().eq(Article::getStatus, 1)
);

// ✅ 分页 + 排除大字段
Page<Article> page = articleMapper.selectPage(
    new Page<>(1, 20),
    Wrappers.<Article>lambdaQuery()
        .select(Article.class, field ->
                !"content".equals(field.getProperty())
                && !"coverImageBase64".equals(field.getProperty()))
        .eq(Article::getStatus, 1)
        .orderByDesc(Article::getPublishTime)
);

// ❌ 冲突：setSqlSelect 优先级更高，会覆盖 select() 的列选择
wrapper.select(Article.class, field -> !"content".equals(field.getProperty()))
       .setSqlSelect("id, title");  // 这行会覆盖上面的 select()

// ⚠️ 危险：如果不小心排除了 del_flag
.select(Article.class, field -> !"delFlag".equals(field.getProperty()))

List<ArticleListVo> list = articleMapper.selectVoList(
    Wrappers.<Article>lambdaQuery()
        .select(Article.class, field -> !"content".equals(field.getProperty()))
        .eq(Article::getStatus, 1)
);