mybatis 多层(三层)嵌套查询

一、java 实体描述

/**
 * <p>
 * 家庭表
 * </p>
 *
 * @author lohas
 */
@Data
@EqualsAndHashCode(callSuper = true)
@TableName("t_family_info")
@ApiModel(value = "FamilyInfoEntity对象", description = "家庭表")
public class FamilyInfoEntity extends Model {

    private static final long serialVersionUID = 1L;

    @ApiModelProperty(value = "主键")
    @TableId(value = "id", type = IdType.INPUT)
    private String id;

    @ApiModelProperty(value = "家庭名称")
    private String familyName;

    @ApiModelProperty(value = "家庭头像url")
    private String headUrl;

    @ApiModelProperty(value = "国家")
    private String country;

    @ApiModelProperty(value = "城市")
    private String city;

    @ApiModelProperty(value = "地址")
    private String address;

    @ApiModelProperty(value = "经度")
    private BigDecimal longitude;

    @ApiModelProperty(value = "纬度")
    private BigDecimal latitude;

    @ApiModelProperty(value = "租户ID")
    private String tenantId;

    @ApiModelProperty(value = "是否删除（0：正常；低于0的数字：已删除）")
    private String deleteFlag;

    @ApiModelProperty(value = "创建人ID")
    private String creatorId;

    @ApiModelProperty(value = "创建时间")
    @JsonDeserialize(using = LocalDateTimeSerializerConfig.LocalDateTimeDeserializer.class)
    @JsonSerialize(using = LocalDateTimeSerializerConfig.LocalDateTimeSerializer.class)
    private LocalDateTime createTime;

    @ApiModelProperty(value = "更新人ID")
    private String updateId;

    @ApiModelProperty(value = "更新时间")
    @JsonDeserialize(using = LocalDateTimeSerializerConfig.LocalDateTimeDeserializer.class)
    @JsonSerialize(using = LocalDateTimeSerializerConfig.LocalDateTimeSerializer.class)
    private LocalDateTime updateTime;

}

/**
 * @author lohas
 * @description
 */
@Data
@ApiModel(value = "RoomDeviceInfoVo对象", description = "房间设备信息实体")
public class RoomDeviceInfoVo implements Serializable {

    @ApiModelProperty(value = "房间id")
    private String roomId;

    @ApiModelProperty(value = "房间名称")
    private String roomName;

    @ApiModelProperty(value = "设备数量")
    private Integer deviceNum;

    @ApiModelProperty(value = "设备信息列表")
    private List<String> deviceIds;
}

/**
 * @author lohas
 * @description
 */
@Data
@ApiModel(value = "FamilyRoomInfoVo对象", description = "家庭房间信息对象实例")
public class FamilyRoomInfoVo extends FamilyInfoEntity {

    @ApiModelProperty(value = "房间设备信息列表")
    private List<RoomDeviceInfoVo> roomDeviceInfoVoList;
}

二、mybatis xml

<?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.lohas.mapper.FamilyInfoMapper">

    <select id="getFamilyRoomInfoVoByUserId" resultMap="familyMap">
		SELECT *
		FROM (
             SELECT tfi.*,
                    trf."id"      AS r_room_id,  --要加上r因为columnPrefix="r_"(如果字段唯一，可以不加)
                    trf.room_name AS r_room_name, --要加上r因为columnPrefix="r_"
                    trd.device_id AS r_d_device_id --要加上r因为columnPrefix="r_"，加上d因为columnPrefix="d_"
             FROM t_user_family tuf
                      LEFT JOIN t_family_info tfi ON tfi.ID = tuf.family_id
                      LEFT JOIN t_family_room tfr ON tuf.family_id = tfr.family_id
                      LEFT JOIN t_room_info trf ON tfr.room_id = trf.ID
                      LEFT JOIN t_room_device trd ON tfr.room_id = trd.room_id
             WHERE tuf.user_id = #{userId}
             ORDER BY tfi.create_time DESC
         ) AS fr,
         (
             SELECT trf."id"             AS r_room_id,  --要加上r因为columnPrefix="r_"
                    COUNT(trd.device_id) AS r_device_num  --要加上r因为columnPrefix="r_"
             FROM t_user_family tuf
                      LEFT JOIN t_family_info tfi ON tfi.ID = tuf.family_id
                      LEFT JOIN t_family_room tfr ON tuf.family_id = tfr.family_id
                      LEFT JOIN t_room_info trf ON tfr.room_id = trf.
                 ID
                      LEFT JOIN t_room_device trd ON tfr.room_id = trd.room_id
             WHERE tuf.user_id = #{userId}
             GROUP BY trf."id"
         ) AS rd
		WHERE fr.r_room_id = rd.r_room_id
	</select>

	<resultMap id="familyMap" type="com.lohas.vo.FamilyRoomInfoVo">
		<!-- 一层： 家庭信息-->
		<id column="id" jdbcType="VARCHAR" property="id"/>
		<result column="family_name" jdbcType="VARCHAR" property="familyName"/>
		<result column="head_url" jdbcType="VARCHAR" property="headUrl"/>
		<result column="country" jdbcType="VARCHAR" property="country"/>
		<result column="city" jdbcType="VARCHAR" property="city"/>
		<result column="address" jdbcType="VARCHAR" property="address"/>
		<result column="longitude" jdbcType="NUMERIC" property="longitude"/>
		<result column="latitude" jdbcType="NUMERIC" property="latitude"/>
		<result column="delete_flag" jdbcType="CHAR" property="deleteFlag"/>
		<result column="creator_id" jdbcType="VARCHAR" property="creatorId"/>
		<result column="create_time" jdbcType="TIMESTAMP" property="createTime"/>
		<result column="update_id" jdbcType="VARCHAR" property="updateId"/>
		<result column="update_time" jdbcType="TIMESTAMP" property="updateTime"/>
		<result column="tenant_id" jdbcType="VARCHAR" property="tenantId"/>
		<!-- 如果字段唯一，可以不加columnPrefix="r_"-->
		<collection property="roomDeviceInfoVoList" columnPrefix="r_" resultMap="roomMap"/>
	</resultMap>

	<resultMap id="roomMap" type="com.lohas.vo.RoomDeviceInfoVo">
		<!-- 二层： 房间信息-->
		<result column="room_id" jdbcType="VARCHAR" property="roomId"/>
		<result column="room_name" jdbcType="VARCHAR" property="roomName"/>
		<result column="device_num" jdbcType="VARCHAR" property="deviceNum"/>
		<!-- 如果字段唯一，可以不加columnPrefix="d_"-->
		<collection property="deviceIds" columnPrefix="d_" resultMap="deviceMap"/>
	</resultMap>

	<resultMap id="deviceMap" type="string">
		<!-- 三层： 设备信息-->
		<result column="device_id" jdbcType="VARCHAR"/>
	</resultMap>

</mapper>

三、调用方法

public interface FamilyInfoMapper extends BaseMapper<FamilyInfoEntity> {

	List<FamilyRoomInfoVo> getFamilyRoomInfoVoByUserId(@Param("userId") String userId);
   
}

四、注意总结

如果你的字段唯一，columnPrefix="r_" 和 columnPrefix="d_"，可以不加，如果你加上了columnPrefix记得在字段上拼接上，否则查询不出数据，拼接要有前后顺序拼接例如：

<collection property="roomDeviceInfoVoList" columnPrefix="r_" resultMap="roomMap"/>

<collection property="deviceIds" columnPrefix="d_" resultMap="deviceMap"/>

r_d_device_id（要加上r因为roomMap columnPrefix="r_"，加上d因为deviceMap columnPrefix="d_"）