MyBatis一對多巢狀查詢的完整例項
阿新 • • 發佈:2021-01-19
前言
巢狀查詢的實現原理為兩次查詢,比如產品表為主表,圖片表為從表通過product_id欄位與產品表id欄位關聯實現一對多,巢狀查詢 首先查詢 主表的資料 然後將主表id欄位賦值給從表實體類中product_id 欄位(productId)然後通過dao介面路徑對映找到對應的MyBatis XMl檔案SQL語句ID如:com.liao.dao.DImgMapper.selectDImgByProductId 進行子查詢也就是第二次查詢。然後返回資料
資料庫建表語句和測試資料如下:
資料庫版本為 MySQL 8.0
產品表
DROP TABLE IF EXISTS `d_product`; CREATE TABLE `d_product` ( `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '產品ID',`product_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin NULL DEFAULT NULL COMMENT '產品名稱',`product_introduction` text CHARACTER SET utf8 COLLATE utf8_bin NULL COMMENT '產品介紹',`product_category` int(11) NULL DEFAULT NULL COMMENT '產品ID',`product_status` int(1) NULL DEFAULT NULL COMMENT '產品狀態',`create_time` datetime(0) NULL DEFAULT NULL COMMENT '建立時間',PRIMARY KEY (`id`) USING BTREE ) ENGINE = InnoDB AUTO_INCREMENT = 18 CHARACTER SET = utf8 COLLATE = utf8_bin COMMENT = '產品表' ROW_FORMAT = Dynamic; INSERT INTO `d_product` VALUES (1,'測試產品名稱修改','測試產品介紹修改',NULL,1,'2020-02-02 12:40:06'); INSERT INTO `d_product` VALUES (2,'產品名稱','產品介紹','2020-03-02 18:15:07'); INSERT INTO `d_product` VALUES (3,'bbb','2020-03-01 22:18:40');
圖片表
DROP TABLE IF EXISTS `d_img`; CREATE TABLE `d_img` ( `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'id',`product_id` int(11) NULL DEFAULT NULL COMMENT '產品圖片ID',`img` varchar(500) CHARACTER SET utf8 COLLATE utf8_bin NULL DEFAULT NULL COMMENT '圖片',PRIMARY KEY (`id`) USING BTREE,INDEX `product_id`(`product_id`) USING BTREE,CONSTRAINT `d_img_ibfk_1` FOREIGN KEY (`product_id`) REFERENCES `d_product` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT ) ENGINE = InnoDB AUTO_INCREMENT = 86 CHARACTER SET = utf8 COLLATE = utf8_bin COMMENT = '產品圖片' ROW_FORMAT = Dynamic; INSERT INTO `d_img` VALUES (40,'1491803633034_683819.jpg','2020-03-03 17:21:20'); INSERT INTO `d_img` VALUES (40,'2020-03-03 17:21:20'); INSERT INTO `d_img` VALUES (41,'1568950881751_702421.jpg','2020-03-03 17:21:20');
Java實體類:
// 將這個註解寫在類上之後,就會忽略類中不存在的欄位,否則可能會報錯 @JsonIgnoreProperties(value = {"handler"}) /** * * TODO: 產品類 * @author LiAo * @date 2020/5/20 17:04 */ public class DProduct { private Integer id; private String productName; private Integer productCategory; private Integer productStatus; private Date createTime; private String productIntroduction; private List<DImg> dImgs; // 用於存放圖片集合 // .. get set toString } /** * * TODO: 產品圖片類 * @author LiAo * @date 2020/5/20 17:05 */ @JsonIgnoreProperties(value = {"handler"}) public class DImg { private Integer id; private Integer productId; private String img; private Date createTime; // .. get set toString }
實體類建立好後要編寫Dao介面 和Mapper XML了
持久層介面DAO:
/** * * TODO: 產品 Dao介面 * @author LiAo * @date 2020/5/20 17:08 */ public interface DProductMapper { /** * 產品圖片一對多巢狀 * @param record 查詢條件 * @return 返回引數 */ List<DProduct> productSelect(DProduct record); }
產品MyBatis xml:
<!--對映的Dao介面類 可以通過這個路徑找到先關的SQL語句和resultMap 對映--> <mapper namespace="com.liao.dao.DProductMapper"> <resultMap id="BaseResultMap" type="com.liao.entity.DProduct"> <id column="id" property="id" jdbcType="INTEGER"/> <result column="product_name" property="productName" jdbcType="VARCHAR"/> <result column="product_category" property="productCategory" jdbcType="INTEGER"/> <result column="product_status" property="productStatus" jdbcType="INTEGER"/> <result column="create_time" property="createTime" jdbcType="TIMESTAMP"/> <result column="product_introduction" property="productIntroduction" jdbcType="LONGVARCHAR"/> </resultMap> <!--產品圖片一對多查詢對映--> <!--id:配置對映的名稱--> <!--type:返回值型別 --> <!--extends:繼承id為BaseResultMap的對映 --> <!--select:子查詢所在的XML繫結的DAO介面路徑.SQL語句id --> <!--column="{productId = id} productId:從表關聯主表的實體類屬性,作為子查詢的條件 id:主表中被關聯的資料庫欄位--> <resultMap id="dProductResultMap" type="com.liao.entity.DProduct" extends="BaseResultMap"> <collection property="dImgs" fetchType="lazy" select="com.liao.dao.DImgMapper.selectDImgByProductId" column="{productId = id}"/> </resultMap> <!--查詢語句--> <select id="productSelect" parameterType="com.liao.entity.DProduct" resultMap="dProductListMapSelect"> select d.id,d.product_name,d.product_category,d.product_status,d.create_time,d.product_introduction from d_product d where 1 = 1 <!-- 使用if標籤拼接條件語句 實現動態SQL--> <if test="id != null and id != ''"> and d.id = #{id} </if> <if test="productName != null and productName != ''"> and d.product_name like concat(#{productName},'%') </if> <if test="productStatus != null and productStatus != ''"> and d.product_status = #{productStatus} </if> <if test="createTime != null and createTime != ''"> and d.create_time like concat(#{createTime},'%') </if> <if test="productIntroduction != null and productIntroduction != ''"> and d.product_introduction like concat(#{productIntroduction},'%') </if> </select> </mapper>
圖片MyBatis xml:
<mapper namespace="com.liao.dao.DImgMapper"> <resultMap id="BaseResultMap" type="com.liao.entity.DImg"> <id column="did" property="id" jdbcType="INTEGER"/> <result column="product_id" property="productId" jdbcType="INTEGER"/> <result column="img" property="img" jdbcType="VARCHAR"/> <result column="create_time" property="createTime" jdbcType="TIMESTAMP"/> </resultMap> <!--一對多巢狀查詢 子查詢語句--> <select id="selectDImgByProductId" resultMap="BaseResultMap"> select i.id as did,i.product_id,i.img,i.create_time from d_img i where i.product_id = #{productId} </select> </mapper>
測試查詢結果
查詢結果為一個產品物件裡有若干個產品圖片物件。
{ "id": 18,"productName": "產品新增圖片上傳測試","productCategory": null,"productStatus": 1,"createTime": "2020-04-14T13:40:40.000+0000","productIntroduction": "產品新增圖片上傳測試","dImgs": [ { "id": 92,"productId": 18,"img": "01.jpg","createTime": "2020-04-26T02:33:04.000+0000" },{ "id": 93,"img": "1554103835292_610234.jpg",{ "id": 94,"img": "1555484699771_582172.jpg",{ "id": 95,"createTime": "2020-04-26T02:33:04.000+0000" } ] },
總結
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