mybatis/mybatis-plus一对多查询

主要是返回数据类型对应关系需要注意一下。具体实现示例如下，

1、查询结果实体类（一对多中的"一"）

package sol.erms.model.entity.process.use;


import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.experimental.Accessors;

import java.io.Serializable;
import java.time.LocalDateTime;
import java.util.Date;
import java.util.List;

/**
 * <p>
 * 借阅记录表/借阅主表导出表
 * </p>
 *
 * @author groot
 * @since 2020-03-18
 */
@Data
public class ErmsUseMainExport implements Serializable {

    private static final long serialVersionUID = 1L;


    /**
     * 借阅编号
     */
    
    private String useNo;

    /**
     * 借阅人
     */
    
    private String ermsLender;

    /**
     * 借阅目的
     */
    
    private String ermsLendingpurpose;

    //条目集合
   
    private List<ERMSUseExport> archList;






}

2、查询结果子对象实体类（一对多中的"多"）

package sol.erms.model.entity.process.use;

import lombok.Data;

import java.util.Date;

@Data
public class ERMSUseExport {

    
    private String archName;

    
    private String archNo;

    
    private String ermsApplymode;

   
    private Date startUseDate;

    
    private String ermsLendhandler;

    
    private String ermsBorrowReviewer;

    
    private Date ermsReturntime;

    
    private Date ermsReturner;

    
    private Date ermsReturnhandler;

    
    private Date ermsReturnReviewer;

}

3、mapper/dao方法：

List<ErmsUseMainExport> getMainListUseCollectionByCondition(Map<String, Object> map);

4、xml中的sql。定义返回数据类型，通过collection标签对应子集即可。

    <resultMap type="sol.erms.model.entity.process.use.ErmsUseMainExport" id="useMainResult">
        <result column="USE_NO" property="useNo" />
        <result column="ERMS_LENDER" property="ermsLender" />
        <result column="ERMS_LENDINGPURPOSE" property="ermsLendingpurpose" />
        <collection property="archList" ofType="sol.erms.model.entity.process.use.ERMSUseExport" column="id">
            <result column="ARCH_NAME" jdbcType="TIMESTAMP" property="archName" />
            <result column="ARCH_NO" jdbcType="VARCHAR" property="archNo" />
            <result column="ERMS_APPLYMODE" property="ermsApplymode" />
            <result column="START_USE_DATE" property="startUseDate" />
            <result column="ERMS_LENDHANDLER" property="ermsLendhandler" />
            <result column="ERMS_BORROW_REVIEWER" property="ermsBorrowReviewer" />
            <result column="ERMS_RETURNTIME" property="ermsReturntime" />
            <result column="ERMS_RETURNER" property="ermsReturner" />
            <result column="ERMS_RETURN_HANDLER" property="ermsReturnhandler" />
            <result column="ERMS_RETURN_REVIEWER" property="ermsReturnReviewer" />
        </collection>
    </resultMap>



<!--条件查询借阅+档案(集合)数据-->
    <select id="getMainListUseCollectionByCondition" resultMap="useMainResult">
        SELECT
            m.`USE_NO`,
            m.`ERMS_LENDER`,
            m.`ERMS_LENDINGPURPOSE`,
            m.ERMS_APPLYMODE,
            u.START_USE_DATE,
            u.ERMS_LENDHANDLER,
            u.ERMS_BORROW_REVIEWER,
            u.ERMS_RETURNTIME,
            u.ERMS_RETURNER,
            u.ERMS_RETURN_HANDLER,
            u.ERMS_RETURN_REVIEWER,
            a.ARCH_NO,
            a.ARCH_NAME
        FROM
            erms_use_main m
            LEFT JOIN erms_use u ON m.ID = u.ERMS_USE_MAIN_ID
            LEFT JOIN erms_archived_arch_ru a ON u.ERMS_ARCH_FORM_ID = a.ID
        <where>
            <if test="DEL_STATUS!=null and DEL_STATUS!=''">
                m.DEL_STATUS = #{DEL_STATUS}
            </if>
            <if test="ids!=null and ids.size()>0">
                m.ID IN
                <foreach collection="ids" item="id" open="(" close=")" separator="," >
                    #{id}
                </foreach>
            </if>
        </where>
    </select>