Mybatis多表连接

程序员文章站 2022-07-12 13:50:50

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Mybatis多表连接

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    文章末尾会附上本文完整的业务需求代码素材，建议你先看末尾，再来看前文。
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                                                                   河南济源普普通通的追梦孩
                                                                           ——爱猫狗的小郝
                                                                             2020/05/06

前言

两种类型

resultType和resultMap都可以完成输出映射：

resultType映射要求sql查询的列名和输出映射pojo类型的属性名一致(不一致可以通过起别名来解决)
resultMap映射时对sql查询的列名和输出映射pojo类型的属性名作一个对应关系。(不一致也无所谓)

resultType ：直接表示返回类型
基本数据类型
复杂数据类型
resultMap ：对外部resultMap的引用
应用场景：
数据库字段信息与对象属性不一致
复杂的联合查询，*控制映射结果
二者不能同时存在，本质上都是Map数据结构

resultMap

解决列名与实体类属性名不一致的问题，同时解决多表连接的查询问题。

操作步骤

分析需求（主查询表、关联查询表）
编写sql语句
resultMap进行映射的思路，在相应的pojo里加关联
编写NewsMapper.xml
编写NewsMapperr.java
单元测试
前端界面展示

resultMap映射问题

resultMap的配置

 <resultMap id="newsResultMap" type="hsy.cool.bean.News">
        <result property="id" column="id"/>
        <result property="title" column="title"/>
        <result property="content" column="content"/>
        <result property="users_id" column="users_id"/>
        <result property="category_id" column="category_id"/>
        <result property="pubtime" column="pubtime"/>
        <result property="keywords" column="keywords"/>
        <result property="state" column="state"/>
        <result property="check_users_id" column="check_users_id"/>
        <result property="check_time" column="check_time"/>
        <result property="is_elite" column="is_elite"/>
    </resultMap>

查询

 <select id="findAllNor" resultMap="newsResultMap">
       select * from n_news
    </select>

java代码

 List<News>findAllNor();

单元测试

@Test
    public void findAllNor(){
        NewsMapper dao= MybatisUtils.getMapper(NewsMapper.class);
        List<News> list=dao.findAllNor();
        Assert.assertNotNull(list);
        Assert.assertEquals(8,list.size());
        String time= DateUtils.parse(list.get(0).getCheck_time());
        Assert.assertEquals("2020-04-10 11:41:40",time);
    }

多表连接——简单

通过增加简单类型的属性实现展⽰多表数据的⽬的

resultMap新增

 <result property="usersName" column="nickname"/>
 <result property="categoryName" column="name"/>
 <result property="checkUsersName" column="nickname"/>

实体类新增属性

    private String usersName;
    private String categoryName;
    private String checkUsersName;
    // setter/getter

单元测试新增

 Assert.assertEquals("匿名",list.get(0).getUsersName());

多表连接——复杂

通过在实体类中添加对象的类型的属性以及assocation标签实现对复杂数据类型的映射

    <resultMap id="newsMapComplex" type="hsy.cool.bean.News">
        <result property="id" column="id"/>
        <result property="title" column="title"/>
        <result property="content" column="content"/>
        <result property="users_id" column="users_id"/>
        <result property="category_id" column="category_id"/>
        <result property="pubtime" column="pubtime"/>
        <result property="keywords" column="keywords"/>
        <result property="state" column="state"/>
        <result property="check_users_id" column="check_users_id"/>
        <result property="check_time" column="check_time"/>
        <result property="is_elite" column="is_elite"/>
        <result property="categoryName" column="name"/>
        <result property="checkUsersName" column="nickname"/>
        <association property="own" javaType="hsy.cool.bean.Users">
            <result property="id" column="id"/>
            <result property="nickname" column="nickname"/>
            <result property="realname" column="realname"/>
            <result property="phone" column="phone"/>
            <result property="email" column="email"/>
            <result property="address" column="address"/>
            <result property="createTime" column="create_time"/>
        </association>
    </resultMap>

查询

 <select id="findAllComplex" resultMap="newsMapComplex">
       select
         n.id,
         title,
         content,
         users_id,
         category_id,
         c.name,
         pubtime,
         keywords,
         state,
         check_users_id,
         u1.nickname,
         check_time,
         is_elite,
         u.*
        from n_news n inner join n_users u on n.users_id=u.id
                       inner join n_category c on n.category_id=c.id
                       inner join n_users u1 on n.check_users_id=u1.id
    </select>

java代码

  List<News>findAllComplex();

实体类新增

  private Users own;
  //setter/getter

单元测试

    @Test
    public void  findAllComplex(){
        NewsMapper dao=MybatisUtils.getMapper(NewsMapper.class);
        List<News> list=dao.findAllComplex();
        Assert.assertNotNull(list);
        Assert.assertEquals(8,list.size());
        String time= DateUtils.parse(list.get(0).getCheck_time());
        Assert.assertEquals("2020-04-10 11:41:40",time);
        Assert.assertEquals("匿名啊啊啊",list.get(0).getOwn().getNickname());
    }

JSP页面修改

          <td class="users">${news.own.nickname}
              <div class="usersInfo">
                  <table>
                      <tr>
                          <td>账号:</td>
                          <td>${news.own.nickname}</td>
                      </tr>

                      <tr>
                          <td>姓名:</td>
                          <td>${news.own.realname}</td>
                      </tr>

                      <tr>
                          <td>电话:</td>
                          <td>${news.own.phone}</td>
                      </tr>

                      <tr>
                          <td>邮件:</td>
                          <td>${news.own.email}</td>
                      </tr>

                      <tr>
                          <td>地址:</td>
                          <td>${news.own.address}</td>
                      </tr>
                  </table>
              </div>
          </td>

java代码修改

List<News> list=newsDao.findAllComplex();

添加样式

    <style type="text/css">
        .usersInfo{
            width: 200px;
            background: #eee;
        }
    </style>

样式修改

    <style type="text/css">
        .usersInfo{
            width: 200px;
            background: #eee;
            position: absolute;
            display: none;
        }
    </style>

导入jquery

    <script type="text/javascript" src="${pageContext.request.contextPath}/js/jquery-1.8.3.min.js">
    </script>

动态样式

    <script>
        //选择器.动作
        $(function(){
            $(".users").hover(function(){
                $(".usersInfo",this).css("display","block");
            },function(){
                $(".usersInfo",this).css("display","none");
            });
        });
    </script>

完整页面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>新闻列表</title>
    <style type="text/css">
        .usersInfo{
            width: 200px;
            background: #eee;
            position: absolute;
            display: none;
        }
    </style>
    <script type="text/javascript" src="${pageContext.request.contextPath}/js/jquery-1.8.3.min.js"></script>
    <script>

        $(function(){
            $(".users").hover(function(){
                $(".usersInfo",this).css("display","block");
            },function(){
                $(".usersInfo",this).css("display","none");
            });
        });
    </script>
</head>
<body>
<p>首页/新闻</p>
<h1>新闻列表</h1>
  <table width="1000" border="1">
      <tr>
          <th>编号</th>
          <th>标题</th>
          <th>内容</th>
          <th>分类</th>
          <th>作者</th>
          <th>关键字</th>
          <th>发布时间</th>
          <th>审批</th>
      </tr>
      <c:forEach items="${list}" var="news">
      <tr>
          <td>${news.id}</td>
          <td>${news.title}</td>
          <td>${news.content}</td>
          <td>${news.categoryName}</td>
          <td class="users">${news.own.nickname}
              <div class="usersInfo">
                  <table>
                      <tr>
                          <td>账号:</td>
                          <td>${news.own.nickname}</td>
                      </tr>

                      <tr>
                          <td>姓名:</td>
                          <td>${news.own.realname}</td>
                      </tr>

                      <tr>
                          <td>电话:</td>
                          <td>${news.own.phone}</td>
                      </tr>

                      <tr>
                          <td>邮件:</td>
                          <td>${news.own.email}</td>
                      </tr>

                      <tr>
                          <td>地址:</td>
                          <td>${news.own.address}</td>
                      </tr>
                  </table>
              </div>
          </td>
          <td>${news.keywords}</td>
          <td>${news.pubtimeString}</td>
          <td>${news.checkUsersName}</td>
      </tr>
      </c:forEach>

  </table>
</body>
</html>

业务素材

数据库表

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 80016
 Source Host           : localhost:3306
 Source Schema         : news

 Target Server Type    : MySQL
 Target Server Version : 80016
 File Encoding         : 65001

 Date: 21/02/2020 16:56:04
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for n_access_logs
-- ----------------------------
DROP TABLE IF EXISTS `n_access_logs`;
CREATE TABLE `n_access_logs`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `ip` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `intime` datetime(0) DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP(0),
  `news_id` int(11) DEFAULT NULL,
  `users_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8 COLLATE = utf8_bin ROW_FORMAT = Dynamic;

-- ----------------------------
-- Table structure for n_category
-- ----------------------------
DROP TABLE IF EXISTS `n_category`;
CREATE TABLE `n_category`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 7 CHARACTER SET = utf8 COLLATE = utf8_bin ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of n_category
-- ----------------------------
INSERT INTO `n_category` VALUES (1, '时事');
INSERT INTO `n_category` VALUES (2, '财经');
INSERT INTO `n_category` VALUES (3, '体育');
INSERT INTO `n_category` VALUES (4, '娱乐');
INSERT INTO `n_category` VALUES (5, '科技');
INSERT INTO `n_category` VALUES (6, '旅游');

-- ----------------------------
-- Table structure for n_news
-- ----------------------------
DROP TABLE IF EXISTS `n_news`;
CREATE TABLE `n_news`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `title` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `content` text CHARACTER SET utf8 COLLATE utf8_bin,
  `users_id` int(11) DEFAULT NULL,
  `category_id` int(11) DEFAULT NULL,
  `pubtime` datetime(0) DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP(0),
  `keywords` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `state` int(11) DEFAULT NULL COMMENT '1=新建，2=审批，3=删除',
  `check_users_id` int(11) DEFAULT NULL,
  `check_time` datetime(0) DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP(0),
  `is_elite` int(11) DEFAULT NULL COMMENT '1=精华，0=非精华',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8 COLLATE = utf8_bin ROW_FORMAT = Dynamic;

-- ----------------------------
-- Table structure for n_replys
-- ----------------------------
DROP TABLE IF EXISTS `n_replys`;
CREATE TABLE `n_replys`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `news_id` int(11) DEFAULT NULL,
  `content` varchar(1024) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `users_id` int(11) DEFAULT NULL,
  `replys_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8 COLLATE = utf8_bin ROW_FORMAT = Dynamic;

-- ----------------------------
-- Table structure for n_short_replys
-- ----------------------------
DROP TABLE IF EXISTS `n_short_replys`;
CREATE TABLE `n_short_replys`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `news_id` int(11) DEFAULT NULL,
  `type` int(11) DEFAULT NULL COMMENT '1=赞，0=踩',
  `create_time` datetime(0) DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP(0),
  `users_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8 COLLATE = utf8_bin ROW_FORMAT = Dynamic;

-- ----------------------------
-- Table structure for n_users
-- ----------------------------
DROP TABLE IF EXISTS `n_users`;
CREATE TABLE `n_users`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `nickname` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
  `realname` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `pwd` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `phone` varchar(20) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `email` varchar(100) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `address` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `create_time` datetime(0) DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP(0),
  `type` int(11) DEFAULT NULL COMMENT '0=管理员，1=读者，2=编辑',
  `realid` varchar(20) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL COMMENT '身份证号',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 3 CHARACTER SET = utf8 COLLATE = utf8_bin ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of n_users
-- ----------------------------
INSERT INTO `n_users` VALUES (1, '管理员', NULL, '123', NULL, NULL, NULL, '2019-10-09 10:06:39', 0, NULL);
INSERT INTO `n_users` VALUES (2, '匿名', NULL, '123', NULL, NULL, NULL, '2019-10-09 10:11:42', 1, NULL);

-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
  `phone` varchar(20) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 23 CHARACTER SET = utf8 COLLATE = utf8_bin ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES (1, '张三', '110');
INSERT INTO `student` VALUES (2, '李四', '120');
INSERT INTO `student` VALUES (3, '王五', '119');
INSERT INTO `student` VALUES (4, '赵六', '110');
INSERT INTO `student` VALUES (15, 'xxx', '111');
INSERT INTO `student` VALUES (16, 'xxx', '111');
INSERT INTO `student` VALUES (17, 'xxx', '111');
INSERT INTO `student` VALUES (18, 'xxx', '111');
INSERT INTO `student` VALUES (19, 'xxx', '111');
INSERT INTO `student` VALUES (20, 'xxx', '111');
INSERT INTO `student` VALUES (21, 'xxx', '111');

-- ----------------------------
-- Table structure for users
-- ----------------------------
DROP TABLE IF EXISTS `users`;
CREATE TABLE `users`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `pwd` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `phone` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `email` varchar(100) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `address` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = utf8 COLLATE = utf8_bin ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of users
-- ----------------------------
INSERT INTO `users` VALUES (1, '张三', '123', '110', '[email protected]', '洛阳');
INSERT INTO `users` VALUES (2, '李四', '111', '110', '[email protected]', '洛阳');
INSERT INTO `users` VALUES (3, '李四', '555', '110', '[email protected]', '洛阳');

SET FOREIGN_KEY_CHECKS = 1;

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完整版请看https://haosy.blog.csdn.net/article/details/105958872

Mybatis多表连接

Mybatis多表连接

前言

两种类型

resultMap

操作步骤

resultMap映射问题

多表连接——简单

多表连接——复杂

JSP页面修改

完整页面

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