mybatis的多表关联查询

• 平时项目中不可避免的会使用多表关联查询。

public R selectPersonInfo(){
    //mybatis会自动把重复数据合并组装。不重复数据放入list中
    List<DemoPersion> demoPersions = demoUserDao.selectPersonInfo("120928001");
    return R.ok(demoPersions);
}

xml文件的写法

<resultMap type="com.standard.modules.demo.entity.DemoPersion" id="demoPerson">
    <result property="collectId" column="COLLECT_ID"></result>
   <!-- 一对多关系 -->
    <collection property="staPostList" ofType="com.standard.modules.homepage.entity.StaPostEntity"
                javaType="java.util.List">
        <result property="isMainPost" column="IS_MAIN_POST"></result>
        <result property="postCode" column="POST_CODE"></result>
        <result property="postName" column="POST_NAME"></result>
    </collection>
</resultMap>

<select id="selectTest" resultMap="demoUserString">
    select 'test_success' test from dual
</select>

<select id="selectPersonInfo" parameterType="java.lang.String"  resultMap="demoPerson">
    SELECT cp.COLLECT_TAG,cp.COLLECT_ID
    ,po.IS_MAIN_POST,po.POST_CODE,po.POST_NAME
    FROM sta_collect_person cp
    left JOIN sta_post po on cp.COLLECT_ID = po.EMPLID
    WHERE cp.EMPLID = ${emplid}
</select>

• 分页插件的使用，使用pagehelper

  package com.standard.config;
  
  import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
  import com.github.pagehelper.PageHelper;
  import org.springframework.context.annotation.Bean;
  import org.springframework.context.annotation.Configuration;
  
  import java.util.Properties;
  
  /**
          * mybatis-plus配置
          *
          */
  @Configuration
  public class MybatisPlusConfig {
  
      /**
       * 分页插件
       */
      @Bean
      public PaginationInterceptor paginationInterceptor() {
          return new PaginationInterceptor();
      }
  
      @Bean
      public PageHelper pageHelper(){
          PageHelper pageHelper = new PageHelper();
          Properties properties = new Properties();
          properties.setProperty("offsetAsPageNum","true");
          properties.setProperty("rowBoundsWithCount","true");
          properties.setProperty("reasonable","true");  //
          properties.setProperty("dialect","mysql");    //配置mysql数据库的方言
          pageHelper.setProperties(properties);
          return pageHelper;
      }
  }
  

  //代码中直接使用
  public R queryLowMark(@RequestBody CollectPersonParam collectPersonParam) {
     Page<Object> result=PageHelper.startPage(collectPersonParam.getPageNum(), collectPersonParam.getPageSize(),true);
     List<StaCollectPersonDTO> list=staHomeService.queryLowMark();
     PageInfo<Object> pageInfo = new PageInfo<>(result.getResult());
     return R.ok(pageInfo);
  }