mybatis-plus使用问题小结

一、多表联合分页查询

1.多表联合查询结果集建议使用VO类，当然也可以使用resultMap

package com.cjhx.tzld.entity.vo;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.cjhx.tzld.entity.TContent;
import com.fasterxml.jackson.annotation.JsonFormat;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;
import org.springframework.format.annotation.DateTimeFormat;
import java.util.Date;
@Data
@ApiModel(value="TContentVo", description="内容池多表联合数据对象")
public class TContentVo extends TContent {
   @ApiModelProperty(value = "编号")
   private Integer cid;
   @ApiModelProperty(value = "内容标题")
   private String title;
   @ApiModelProperty(value = "作者Id")
   @TableField("authorId")
   private Integer authorId;
   @ApiModelProperty(value = "时间")
   @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss",timezone = "GMT+8") //返回时间类型
   @DateTimeFormat(pattern="yyyy-MM-dd HH:mm:ss") //接收时间类型
   private Date time;
   @ApiModelProperty(value = "内容")
   private String content;
   @ApiModelProperty(value = "作者姓名")
   private String author;
   @ApiModelProperty(value = "话题")
   private String topic;
   @ApiModelProperty(value = "模块编号")
   private int moduleNum;
   @ApiModelProperty(value = "模块")
   private String module;
   public TContentVo() {
   }
   public TContentVo(Integer cid, String title, Date time, String content, String author, String topic, int moduleNum) {
       this.cid = cid;
       this.title = title;
       this.time = time;
       this.content = content;
       this.author = author;
       this.topic = topic;
       this.moduleNum = moduleNum;
}

2.controller

package com.cjhx.tzld.controller;

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.cjhx.tzld.common.Result;
import com.cjhx.tzld.entity.TContent;
import com.cjhx.tzld.entity.TContentRelationFund;
import com.cjhx.tzld.entity.TTopicPk;
import com.cjhx.tzld.entity.vo.TContentVo;
import com.cjhx.tzld.service.TContentService;
import io.swagger.annotations.*;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import javax.annotation.Resource;
import java.util.Date;
import java.util.List;
/**
* @since 2022-02-28
*/
@RestController
@RequestMapping("/content")
@Api("内容池模块")
public class ContentController {
   @Resource
   private TContentService contentService;
   @ApiImplicitParams({
           @ApiImplicitParam(name = "cid",value = "cid",dataType = "int",defaultValue = "0",required = false),
           @ApiImplicitParam(name = "title",value = "标题",dataType = "String",defaultValue = "",required = false),
           @ApiImplicitParam(name = "author",value = "作者姓名",dataType = "String",defaultValue = "",required = false),
           @ApiImplicitParam(name = "time",value = "发布时间",dataType = "Date",defaultValue = "",required = false),
           @ApiImplicitParam(name = "content",value = "内容",dataType = "String",defaultValue = "",required = false),
           @ApiImplicitParam(name = "topic",value = "话题",dataType = "String",defaultValue = "",required = false),
           @ApiImplicitParam(name = "moduleNum",value = "投放模块 1热点速递 2基会直达",dataType = "int",defaultValue = "",required = false),
           @ApiImplicitParam(name = "pageIndex",value = "页码",dataType = "int",defaultValue = "1",required = false),
           @ApiImplicitParam(name = "pageSize",value = "每页数量",dataType = "int",defaultValue = "10",required = false)
   })
   @ApiResponses({
           @ApiResponse(code = 200,message = "OK",response = TContent.class)
   @ApiOperation(value="分页获取内容接口(Web端)", notes="支持多条件查询",httpMethod = "GET")
   @RequestMapping(value = "/getContentPage",method = RequestMethod.GET)
   public Result getContentPage(@RequestParam(defaultValue = "0",required = false) int cid,
                                @RequestParam(defaultValue = "",required = false) String title,
                                @RequestParam(defaultValue = "",required = false) String author,
                                @RequestParam(required = false) Date time,
                                @RequestParam(defaultValue = "",required = false) String content,
                                @RequestParam(defaultValue = "",required = false) String topic,
                                @RequestParam(defaultValue = "0",required = false) int moduleNum,
                                @RequestParam(defaultValue = "1",required = false) int pageIndex,
                                @RequestParam(defaultValue = "10",required = false)  int pageSize) throws Exception{
       try {
           IPage<TContentVo> byPage = contentService.findByPage(new Page<TContentVo>(pageIndex, pageSize),new TContentVo(cid, title, time, content, author,  topic, moduleNum));
           return Result.success(byPage);
       }catch (Exception e){
           return Result.serviceFail(e.getMessage());
       }
   }
}

3.service

package com.cjhx.tzld.service.impl;

import com.baomidou.mybatisplus.core.conditions.Wrapper;
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.cjhx.tzld.common.PageUtil;
import com.cjhx.tzld.entity.TContent;
import com.cjhx.tzld.entity.vo.TContentVo;
import com.cjhx.tzld.mapper.TContentMapper;
import com.cjhx.tzld.service.TContentService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
import java.util.Date;
/**
* @since 2022-02-28
*/
@Service
public class TContentServiceImpl extends ServiceImpl<TContentMapper, TContent> implements TContentService {
   @Resource
   private TContentMapper tContentMapper;
   @Override
   public IPage<TContentVo> findByPage(Page<TContentVo> page, TContentVo contentVo) {
       return tContentMapper.findByPage(page,contentVo);
   }
}

4.mapper

package com.cjhx.tzld.mapper;

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.cjhx.tzld.entity.TContent;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.cjhx.tzld.entity.vo.TContentVo;
import org.apache.ibatis.annotations.Param;
/**
* @since 2022-02-28
*/
public interface TContentMapper extends BaseMapper<TContent> {
   IPage<TContentVo> findByPage(Page<TContentVo> page, @Param("contentVo") TContentVo contentVo);
}

5.mapper.xml，注意入参contentVo

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.cjhx.tzld.mapper.TContentMapper">

<select id="findByPage" resultType="com.cjhx.tzld.entity.vo.TContentVo" parameterType="com.cjhx.tzld.entity.vo.TContentVo">
       SELECT t.`cid`,t.`authorId`,a.`name`,t.`title`,t.`time`,t.`content`,p.`topic`,h.`title` AS `module`
       FROM `t_content` t
       LEFT JOIN `t_author` a ON a.`aid`=t.`authorId`
       LEFT JOIN `t_topic_pk` p ON p.`cid` = t.`cid`
       LEFT JOIN `t_hot_express` h ON h.`cid` = t.`cid`
       UNION ALL
       SELECT t.`cid`,t.`authorId`,a.`name`,t.`title`,t.`time`,t.`content`,p.`topic`,f.`title` AS `module`
       LEFT JOIN `t_fund_point` f ON f.`cid` = t.`cid`
       <where>
           1=1
           <if test="contentVo.cid > 0"> and cid = #{contentVo.cid}</if>
           <if test="contentVo.title != null and contentVo.title != ''"> and t.title like concat('％', #{contentVo.title}, '％')</if>
           <if test="contentVo.author != null and contentVo.author != ''"> and a.author like concat('％', #{contentVo.author}, '％')</if>
           <if test="contentVo.time != null"> and t.time =${contentVo.time}</if>
           <if test="contentVo.content != null and contentVo.content != ''"> and t.content like concat('％', #{contentVo.content}, '％')</if>
           <if test="contentVo.topic != null and contentVo.topic != ''"> and p.topic like concat('％', #{contentVo.topic}, '％')</if>
           <if test="contentVo.moduleNum == 1"> and f.currentState = -1</if>
           <if test="contentVo.moduleNum == 2"> and h.currentState = -1</if>
       </where>
       order by time desc
   </select>
</mapper>

二、找不到mapper

首先排除@MapperScan("com.cjhx.tzld.mapper")已添加

1.首先配置文件扫描，mapper-locations:classpath:/com/cjhx/tzld/mapper/xml/*.xml

mybatis-plus:
 configuration:
   log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
 mapper-locations: classpath:/com/cjhx/tzld/mapper/xml/*.xml

2.在pom.xml的<build>添加xml资源

<build>
       <plugins>
           <plugin>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-maven-plugin</artifactId>
           </plugin>
       </plugins>
       <resources>
           <!--引入mapper对应的xml文件-->
           <resource>
               <directory>src/main/java</directory>
               <includes>
                   <include>**/*.xml</include>
               </includes>
           </resource>
       </resources>
   </build>

来源：https://www.cnblogs.com/zeussbook/p/15949379.html