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display: inline-block;">6</div>SQL映射文件之自定义映射元素</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-95d837d1 data-v-95d837d1><div class="item" data-v-95d837d1><div class="indicator" data-v-95d837d1></div><a class="VPLink link link" href="/courses/mybatis/01-MyBatis%E5%9F%BA%E7%A1%80/07-SQL%E6%98%A0%E5%B0%84%E6%96%87%E4%BB%B6%E4%B9%8B%E7%BC%93%E5%AD%98%E5%85%83%E7%B4%A0" data-v-95d837d1><!--[--><p class="text" data-v-95d837d1><div class="text-color-gray mr-[6px]" style="font-weight: 550; display: inline-block;">7</div>SQL映射文件之缓存元素</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-95d837d1 data-v-95d837d1><div class="item" data-v-95d837d1><div class="indicator" data-v-95d837d1></div><a class="VPLink link link" href="/courses/mybatis/01-MyBatis%E5%9F%BA%E7%A1%80/08-%E5%8A%A8%E6%80%81SQL" data-v-95d837d1><!--[--><p class="text" data-v-95d837d1><div class="text-color-gray mr-[6px]" style="font-weight: 550; display: inline-block;">8</div>动态SQL</p><!--]--></a><!----></div><!----></div><!--]--></div></section></div><div class="group" data-v-802ad7d8><section class="VPSidebarItem level-0 collapsible" data-v-802ad7d8 data-v-95d837d1><div class="item" role="button" tabindex="0" data-v-95d837d1><div class="indicator" data-v-95d837d1></div><h2 class="text" data-v-95d837d1>MyBatis-Plus基础 (5篇)</h2><div class="caret" role="button" aria-label="toggle section" tabindex="0" data-v-95d837d1><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" viewbox="0 0 24 24" class="caret-icon" data-v-95d837d1><path d="M9,19c-0.3,0-0.5-0.1-0.7-0.3c-0.4-0.4-0.4-1,0-1.4l5.3-5.3L8.3,6.7c-0.4-0.4-0.4-1,0-1.4s1-0.4,1.4,0l6,6c0.4,0.4,0.4,1,0,1.4l-6,6C9.5,18.9,9.3,19,9,19z"></path></svg></div></div><div class="items" data-v-95d837d1><!--[--><div class="VPSidebarItem level-1 is-link" data-v-95d837d1 data-v-95d837d1><div class="item" data-v-95d837d1><div class="indicator" data-v-95d837d1></div><a class="VPLink link link" href="/courses/mybatis/02-MyBatis-Plus%E5%9F%BA%E7%A1%80/01-%E5%BF%AB%E9%80%9F%E5%85%A5%E9%97%A8" data-v-95d837d1><!--[--><p class="text" data-v-95d837d1><div class="text-color-red mr-[6px]" style="font-weight: 550; display: inline-block;">1</div>快速入门</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-95d837d1 data-v-95d837d1><div class="item" data-v-95d837d1><div class="indicator" data-v-95d837d1></div><a class="VPLink link link" href="/courses/mybatis/02-MyBatis-Plus%E5%9F%BA%E7%A1%80/02-%E5%A2%9E%E5%88%A0%E6%94%B9%E6%93%8D%E4%BD%9C" data-v-95d837d1><!--[--><p class="text" data-v-95d837d1><div class="text-color-orange mr-[6px]" style="font-weight: 550; display: inline-block;">2</div>增删改操作</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-95d837d1 data-v-95d837d1><div class="item" data-v-95d837d1><div class="indicator" data-v-95d837d1></div><a class="VPLink link link" href="/courses/mybatis/02-MyBatis-Plus%E5%9F%BA%E7%A1%80/03-%E7%AE%80%E5%8D%95%E6%9F%A5%E8%AF%A2%E6%93%8D%E4%BD%9C" data-v-95d837d1><!--[--><p class="text" data-v-95d837d1><div class="text-color-yellow mr-[6px]" style="font-weight: 550; display: inline-block;">3</div>简单查询操作</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-95d837d1 data-v-95d837d1><div class="item" data-v-95d837d1><div class="indicator" data-v-95d837d1></div><a class="VPLink link link" href="/courses/mybatis/02-MyBatis-Plus%E5%9F%BA%E7%A1%80/04-%E6%9D%A1%E4%BB%B6%E6%9E%84%E9%80%A0%E5%99%A8" data-v-95d837d1><!--[--><p class="text" data-v-95d837d1><div class="text-color-gray mr-[6px]" style="font-weight: 550; display: inline-block;">4</div>条件构造器</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-95d837d1 data-v-95d837d1><div class="item" data-v-95d837d1><div class="indicator" data-v-95d837d1></div><a class="VPLink link link" href="/courses/mybatis/02-MyBatis-Plus%E5%9F%BA%E7%A1%80/05-%E4%BB%A3%E7%A0%81%E7%94%9F%E6%88%90%E5%99%A8" data-v-95d837d1><!--[--><p class="text" data-v-95d837d1><div class="text-color-gray mr-[6px]" style="font-weight: 550; display: inline-block;">5</div>代码生成器</p><!--]--></a><!----></div><!----></div><!--]--></div></section></div><!--]--><!--[--><!--]--></nav></aside><div class="VPContent has-sidebar" id="VPContent" data-v-03322d68 data-v-2c336b25><div class="VPDoc has-sidebar has-aside" data-v-2c336b25 data-v-53ed897c><!--[--><!--]--><div class="container" data-v-53ed897c><div class="aside" data-v-53ed897c><div class="aside-curtain" data-v-53ed897c></div><div class="aside-container" data-v-53ed897c><div class="aside-content" data-v-53ed897c><div class="VPDocAside" data-v-53ed897c data-v-3d450548><!--[--><!--]--><!--[--><!--]--><div class="VPDocAsideOutline" role="navigation" data-v-3d450548 data-v-70b38f01><div class="content" data-v-70b38f01><div class="outline-marker" data-v-70b38f01></div><div class="outline-title" role="heading" aria-level="2" data-v-70b38f01>目录</div><nav aria-labelledby="doc-outline-aria-label" data-v-70b38f01><span class="visually-hidden" id="doc-outline-aria-label" data-v-70b38f01> Table of Contents for current page </span><ul class="root" data-v-70b38f01 data-v-e10534d6><!--[--><!--]--></ul></nav></div></div><!--[--><!--]--><div class="spacer" data-v-3d450548></div><!--[--><!--]--><!----><!--[--><!--]--><!--[--><!--]--></div></div></div></div><div class="content" data-v-53ed897c><div class="content-container" data-v-53ed897c><!--[--><!--]--><!----><main class="main" data-v-53ed897c><div style="position:relative;" class="vp-doc _courses_mybatis_01-MyBatis%E5%9F%BA%E7%A1%80_04-SQL%E6%98%A0%E5%B0%84%E6%96%87%E4%BB%B6%E4%B9%8B%E6%9F%A5%E8%AF%A2%E5%85%83%E7%B4%A0" data-v-53ed897c><div><h1 id="sql映射文件之查询元素" tabindex="-1">SQL映射文件之查询元素 <a class="header-anchor" href="#sql映射文件之查询元素" aria-label="Permalink to "SQL映射文件之查询元素""></a></h1><!----><h2 id="前言" tabindex="-1">前言 <a class="header-anchor" href="#前言" aria-label="Permalink to "前言""></a></h2><p><strong>C：</strong> 在上一篇，笔者带大家对 MyBatis 的核心配置文件做了介绍。本篇开始，笔者将带你学习 MyBatis 的 SQL 映射文件，它是 MyBatis 中亮点最多的部分（翻回去看看 MyBatis 特点，主要优势都在这儿），同时也是未来我们使用 MyBatis 开发时接触最多的部分。</p><p>不过你也别担心，MyBatis 在 SQL 语句映射方面异常强大，但 SQL 映射文件却是相当简单。</p><p>下方是 SQL 映射文件的标签模板，笔者将花两三篇对其中常用的一些标签的常用使用方式进行介绍。</p><p><strong>mapper</strong> 根标签</p><ul><li>cache-ref 引用其它命名空间的缓存配置</li><li><strong>cache</strong> 配置给定命名空间的缓存</li><li><em><strong>resultMap</strong></em> （自定义结果集映射配置）用来描述数据库结果集和对象的对应关系，是最复杂也是最强大的元素</li><li><s>parameterMap</s> （自定义参数映射配置）此元素已被废弃，并可能在将来被移除！请使用行内参数映射。</li><li><strong>sql</strong> 可以重用的 SQL 块</li><li><strong>insert</strong> 映射插入语句</li><li><strong>update</strong> 映射更新语句</li><li><strong>delete</strong> 映射删除语句</li><li><strong>select</strong> 映射查询语句</li></ul><p><img src="/assets/202012271107691.6QQ7R8Hv.png" alt="202012271107691"></p><h2 id="mapper元素" tabindex="-1">mapper元素 <a class="header-anchor" href="#mapper元素" aria-label="Permalink to "mapper元素""></a></h2><p>mapper 元素是 SQL 映射文件的根标签，在该标签内有一个属性 namespace（命名空间），可以理解为当前 SQL 映射文件的标识。</p><p><strong>传统 SqlSession 开发中</strong> ，mapper 元素的 namespace 属性和下方子元素的 id 属性联合保证了 SQL 语句的唯一标识。</p><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><?</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">xml</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> version</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"1.0"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> encoding</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"UTF-8"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">?></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><!</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">DOCTYPE</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> mapper</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">"http://mybatis.org/dtd/mybatis-3-mapper.dtd"></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">mapper</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> namespace</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"userMapper"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> <</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectList"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> SELECT * FROM `user`</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> </</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">mapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">List</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;"><</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">> </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">userList</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectList</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"userMapper.selectList"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span></code></pre></div><p><strong>SqlSession 的 Mapper 接口开发中</strong> ，mapper 元素的 namespace 属性必须命名为对应的 Mapper 接口的全限定类名，下方子元素也要和对应 Mapper 接口中的方法一 一对应。</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">package</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> com.example.mapper;</span></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">// ...略...</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> interface</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
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<span class="line"></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> /**</span></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * 查询用户列表</span></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@return</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> /</span></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> */</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List<</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">> </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectList</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">();</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> </span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><?</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">xml</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> version</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"1.0"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> encoding</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"UTF-8"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">?></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><!</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">DOCTYPE</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> mapper</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">"http://mybatis.org/dtd/mybatis-3-mapper.dtd"></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">mapper</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> namespace</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"com.example.mapper.UserMapper"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> <!-- List<User> selectList(); --></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> <</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectList"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> SELECT * FROM `user`</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> </</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">mapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><div class="tip custom-block"><p class="custom-block-title">笔者说</p><p>Mapper 接口开发是我们上篇中最后部分讲解过的 SqlSession 使用方式，以后也是主要的写法，很好理解，GKD掌握。</p></div><h2 id="select元素" tabindex="-1">select元素 <a class="header-anchor" href="#select元素" aria-label="Permalink to "select元素""></a></h2><p>在每一个项目中，查询都是应用最频繁也是应用最困难的部分。 在 SQL 映射文件中，select 元素就是用于编写查询 SQL 的，它是 MyBatis 中最常用的元素之一。</p><p>select 元素有很多属性，可以很详细的来配置每条语句的行为细节。</p><ul><li><p><strong>id</strong> 命名空间中唯一的标识符</p><p>Mapper 接口开发中，id 值需要和接口中对应方法的名字保持一致</p></li><li><p><strong>parameterType</strong> 传入SQL语句的参数类型</p><p>可以为参数类型的全限定类名或别名</p><p>Mapper接口开发中，parameterType 值需要和接口中对应方法的参数类型保持一致</p></li><li><p><strong>resultType</strong> SQL语句返回值类型（详细解释见 resultMap 元素部分）</p><p>可以为返回值类型的全限定类名或别名</p><p>Mapper接口开发中，resultType 值需要和接口中对应方法的返回值类型保持一致</p><p><strong>注意：</strong> 如果返回值类型是集合，那么 resultType 值应该表示为集合的泛型类型，而不是集合类型。</p></li></ul><p>接下来，笔者通过几个示例来带大家掌握下 select 元素的使用。</p><div class="tip custom-block"><p class="custom-block-title">笔者说</p><p>笔者只是介绍了使用最为频繁的几个属性，如果想了解更多的属性含义，可以前往<a href="https://mybatis.org/mybatis-3/zh/sqlmap-xml.html" target="_blank" rel="noreferrer">官网</a>查看。</p></div><h3 id="用户名查询" tabindex="-1">用户名查询 <a class="header-anchor" href="#用户名查询" aria-label="Permalink to "用户名查询""></a></h3><p>在《快速入门》篇的数据库基础上，我们先来实现一个根据用户名的模糊查询。</p><p>首先，在 Mapper 接口中我们添加一个方法。</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> interface</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
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<span class="line"></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> /**</span></span>
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||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * 根据用户名模糊查询</span></span>
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||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> name</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 用户名</span></span>
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||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@return</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 用户列表</span></span>
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||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> */</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List<</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">> </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByName</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(String </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
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<span class="line"></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p>然后我们在 SQL 映射文件中再添加一个与该方法对应的查询元素。</p><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- List<User> selectByName(String name); --></span></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- 通过#{参数名}即可获取传入的值 --></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectByName"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> parameterType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"string"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> select * from user where name like concat('%', #{name}, '%')</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><p>测试一下：</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> TestMyBatis</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
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<span class="line"></span>
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||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Test</span></span>
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||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> void</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;"> testSelectByName</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">throws</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> IOException {</span></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 获取SqlSession对象</span></span>
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||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> try</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (SqlSession</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> MyBatisUtils.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">openSession</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">()) {</span></span>
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<span class="line"></span>
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||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 获取 Mapper 接口</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(UserMapper.class);</span></span>
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||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 执行 SQL</span></span>
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||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;"><</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">> </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">userList</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByName</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"J"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
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||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 遍历数据</span></span>
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||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userList.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">forEach</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(System.out</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">::</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">println);</span></span>
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||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> } </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">catch</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (Exception </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">e</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) {</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> e.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">printStackTrace</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">();</span></span>
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||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> }</span></span>
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||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> }</span></span>
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||
<span class="line"></span>
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||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p><strong>控制台输出：</strong></p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">-- 输出的 SQL 语句</span></span>
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||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">select</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> *</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> from</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">where</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> like</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> concat</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">'%'</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, ?, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">'%'</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">)</span></span></code></pre></div><div class="language- vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang"></span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span>User [id=1, name=Jone, age=18, email=Jone@126.com]</span></span>
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<span class="line"><span>User [id=2, name=Jack, age=20, email=Jack@126.com]</span></span></code></pre></div><h4 id="和-的区别" tabindex="-1">#{}和${}的区别 <a class="header-anchor" href="#和-的区别" aria-label="Permalink to "#{}和${}的区别""></a></h4><p>在控制台输出的 MyBatis 日志中，我们可以看到最后执行的 SQL 就是我们在传统 JDBC 开发中，为了解决 SQL 注入攻击而编写的 SQL 形式。</p><p>之所以输出如此，是因为我们使用了 #{} 的形式来使用参数，#{}表示一个占位符号，可以接收简单类型值或 POJO 属性值，通过 #{} 可以实现 preparedStatement 向占位符中设置值，自动进行 Java 类型和 JDBC 类型转换。#{} 可以有效防止 SQL 注入。</p><p><strong>注意：</strong> #{} 占位符不能放置在字符串中，即：select * from user where name like '%#{name}%' 是错误的。</p><hr><p>其实在 MyBatis 中还有占位符：${}，但是基本不使用，至于原因，我们试试看就知道了。</p><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- List<User> selectByName(String name); --></span></span>
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<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- ${参数名} 可以直接放在字符串中 --></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectByName"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> parameterType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"string"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> select * from user where name like '%${name}%'</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><p><strong>控制台输出：</strong></p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">-- 输出的 SQL 语句</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">select</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> *</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> from</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">where</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> like</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;"> '%J%'</span></span></code></pre></div><p>这回知道原因了吧？ <strong>总结一下它们的区别（面试题）</strong> ：</p><ul><li>在使用<code>#{}</code>参数语法时，MyBatis 会创建 <code>PreparedStatement</code> 参数占位符，并通过占位符安全地设置参数（就像使用 ? 一样）[1]</li><li>在使用 <code>${}</code> 时，MyBatis 会将 SQL 中的 <code>${}</code> 替换成对应变量的值。适合需要直接插入一个不转义的字符串时使用。</li><li>使用 #{} 可以有效的防止 SQL 注入，提高系统安全性。</li></ul><h3 id="多参数查询" tabindex="-1">多参数查询 <a class="header-anchor" href="#多参数查询" aria-label="Permalink to "多参数查询""></a></h3><p>我们也都知道，在 Java 中定义方法的时候，返回值类型只能设定为一个具体类型，但是方法的参数是可以定义 N 个的，那么在面对这种方法时，MyBatis 查询元素的 parameterType 该如何使用呢？</p><p>其实也非常简单，<strong>有三种方式比较流行</strong> ：</p><ul><li>将多个参数封装到 POJO / 自定义对象中</li><li>将多个参数封装到 Map / List 集合中</li><li>将多个参数通过 @Param 注解标注</li></ul><p>我们通过一个案例感受下不同方式的区别： <strong>案例需求：根据用户名、年龄查询用户列表</strong></p><h4 id="封装到pojo" tabindex="-1">封装到POJO <a class="header-anchor" href="#封装到pojo" aria-label="Permalink to "封装到POJO""></a></h4><p>首先，在 Mapper 接口中我们添加一个方法。</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> interface</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> /**</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * 根据用户名和年龄查询</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> user</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 用户信息</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@return</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 用户列表</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> */</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List<</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">> </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByUser</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(User </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">user</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p>然后我们在 SQL 映射文件中再添加一个与该方法对应的查询元素。</p><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- List<User> selectByUser(User user); --></span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- 在 parameterType 为对象时, #{属性名} 可以获取对象中的属性值 --></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectByUser"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> parameterType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> select</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> * </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> from</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> where </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> name like concat('%', #{name}, '%')</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> and age = #{age}</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><p>测试一下：</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> TestMyBatis</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Test</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> void</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;"> testSelectByUser</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">throws</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> IOException {</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 获取SqlSession对象</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> try</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (SqlSession</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> MyBatisUtils.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">openSession</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">()) {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 获取 Mapper 接口</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(UserMapper.class);</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 执行 SQL</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> new</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">();</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">setName</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"J"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">setAge</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;"><</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">> </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">userList</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByUser</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(user);</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 遍历数据</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userList.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">forEach</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(System.out</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">::</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">println);</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> } </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">catch</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (Exception </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">e</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) {</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> e.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">printStackTrace</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">();</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> }</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> }</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p><strong>控制台输出：</strong></p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">-- 输出的 SQL 语句</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">select</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> *</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> from</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">where</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> like</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> concat</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">'%'</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, ?, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">'%'</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">and</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> age </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> ?</span></span></code></pre></div><div class="language- vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang"></span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span>User [id=2, name=Jack, age=20, email=Jack@126.com]</span></span></code></pre></div><h4 id="封装到map集合" tabindex="-1">封装到Map集合 <a class="header-anchor" href="#封装到map集合" aria-label="Permalink to "封装到Map集合""></a></h4><div class="tip custom-block"><p class="custom-block-title">笔者说</p><p>笔者个人比较喜欢这一种，Map 集合总是那么"万金油"。</p></div><p>首先，在 Mapper 接口中我们添加一个方法。</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> interface</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> /**</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * 根据用户名和年龄查询</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> params</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 条件参数</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@return</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 用户列表</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> */</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List<</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">> </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByMap</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(Map<</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">String</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Object</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">> </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">params</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p>然后我们在 SQL 映射文件中再添加一个与该方法对应的查询元素。</p><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- List<User> selectByMap(Map<String, Object> params); --></span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- 在 parameterType 为 Map 集合时, #{map的键名} 可以获取集合的值 --></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectByMap"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> parameterType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"map"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> select</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> * </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> from</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> where </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> name like concat('%', #{name}, '%')</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> and age = #{age}</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><p>测试一下：</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> TestMyBatis</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Test</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> void</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;"> testSelectByMap</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">throws</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> IOException {</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 获取SqlSession对象</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> try</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (SqlSession</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> MyBatisUtils.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">openSession</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">()) {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 获取 Mapper 接口</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(UserMapper.class);</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 执行 SQL</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> Map</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;"><</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">String</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Object</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">> </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">params</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> new</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> HashMap<>();</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> params.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">put</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"name"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"J"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> params.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">put</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"age"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;"><</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">> </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">userList</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByMap</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(params);</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 遍历数据</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userList.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">forEach</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(System.out</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">::</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">println);</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> } </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">catch</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (Exception </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">e</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) {</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> e.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">printStackTrace</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">();</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> }</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> }</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p><strong>控制台输出：</strong></p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">-- 输出的 SQL 语句</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">select</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> *</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> from</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">where</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> like</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> concat</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">'%'</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, ?, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">'%'</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">and</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> age </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> ?</span></span></code></pre></div><div class="language- vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang"></span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span>User [id=2, name=Jack, age=20, email=Jack@126.com]</span></span></code></pre></div><h4 id="param注解" tabindex="-1">@Param注解 <a class="header-anchor" href="#param注解" aria-label="Permalink to "@Param注解""></a></h4><div class="tip custom-block"><p class="custom-block-title">笔者说</p><p>@Param 注解与上述两种方式有些不同，如果你使用了该注解，那么 parameterType 就不需要再手动指定了，使用 <strong>普通类型参数</strong> （Java中的 int、double、String...... 这些都属于普通类型参数，而对象和集合就不属于普通类型参数了）的方法一般都推荐使用它。</p></div><p>首先，在 Mapper 接口中我们添加一个方法。</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> interface</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> /**</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * 根据用户名和年龄查询</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> name</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 用户名</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> age</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 年龄</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@return</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 用户列表</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> */</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // @Param("参数名") 注解中传入的参数名才是占位符要使用到的名字</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List<</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">> </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByParam</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Param</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"name"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) String </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Param</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"age"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) Integer </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">age</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p>然后我们在 SQL 映射文件中再添加一个与该方法对应的查询元素。</p><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- List<User> selectByParam(@Param("name") String name, @Param("age") Integer age); --></span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- #{@Param注解设定的名} 可以用来取出对应参数的值 --></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectByParam"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> select</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> * </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> from</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> where </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> name like concat('%', #{name}, '%')</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> and age = #{age}</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><p>测试一下：</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> TestMyBatis</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Test</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> void</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;"> testSelectByParam</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">throws</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> IOException {</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 获取SqlSession对象</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> try</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (SqlSession</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> MyBatisUtils.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">openSession</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">()) {</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 获取 Mapper 接口</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> sqlSession.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(UserMapper.class);</span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 执行 SQL</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> List</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;"><</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">> </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">userList</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByParam</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"j"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> // 遍历数据</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userList.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">forEach</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(System.out</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">::</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">println);</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> } </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">catch</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (Exception </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">e</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) {</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> e.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">printStackTrace</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">();</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> }</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> }</span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p><strong>控制台输出：</strong></p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">-- 输出的 SQL 语句</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">select</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> *</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> from</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">where</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> like</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> concat</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">'%'</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, ?, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">'%'</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">and</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> age </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> ?</span></span></code></pre></div><div class="language- vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang"></span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span>User [id=2, name=Jack, age=20, email=Jack@126.com]</span></span></code></pre></div><div class="warning custom-block"><p class="custom-block-title">使用注意</p><p>超过 3 个以上的 <strong>普通类型参数</strong> 最好封装成对象或 Map 来入参（特别是在常规的增加和修改操作时，字段较多，封装成对象比较方便），而参数固定的业务方法，最好使用 @Param 来入参（这种方法比较灵活，代码的可读性高，可以清晰看出来这个接口方法的所需的参数是什么，并且对于固定的接口方法，参数一般是固定的，所以可以使用直接参数入参即可，无需封装对象。例如：修改个人密码的方法，根据 id 删除用户的方法，根据 id 查看用户明细的方法，都可以采取这种方式）</p></div><h2 id="sql元素" tabindex="-1">sql元素 <a class="header-anchor" href="#sql元素" aria-label="Permalink to "sql元素""></a></h2><p>在同一个 SQL 映射文件中，经常面临着重复 SQL 的问题，尤其是查询类 SQL 。效果如下：</p><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectByName"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> select </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> id, name, age, email</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> from</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> where name like concat('%', #{name}, '%')</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectById"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> select </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> id, name, age, email</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> from</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> where id = #{id}</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><p>使用 sql 元素可以让我们得以复用一些 SQL语句。</p><div class="language-xml vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">xml</span><pre class="shiki shiki-themes github-light github-dark-dimmed vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"><!-- 定义可重用 SQL 段 --></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">sql</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectUser"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> select </span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> id, name, age, email</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> from</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">sql</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectByName"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> <!-- 引用 SQL --></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> <</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">include</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> refid</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectUser"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">/></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> where name like concat('%', #{name}, '%')</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"><</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> id</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectById"</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> resultType</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"User"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> <</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">include</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> refid</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">"selectUser"</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">/></span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> where id = #{id}</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"></</span><span style="--shiki-light:#22863A;--shiki-dark:#8DDB8C;">select</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">></span></span></code></pre></div><h2 id="参考文献" tabindex="-1">参考文献 <a class="header-anchor" href="#参考文献" aria-label="Permalink to "参考文献""></a></h2><p>[1]MyBatis 官网. XML 映射文件[EB/OL]. <a href="https://mybatis.org/mybatis-3/zh/sqlmap-xml.html" target="_blank" rel="noreferrer">https://mybatis.org/mybatis-3/zh/sqlmap-xml.html</a>. 2020-12-26</p><h2 id="后记" tabindex="-1">后记 <a class="header-anchor" href="#后记" aria-label="Permalink to "后记""></a></h2><p>本篇中，select 元素是重点，笔者列了好多个示例，你一定要将示例代码完整"临摹" + "思考"一遍，这样才能达到笔者所说的技术学习的第二步、第三步。</p><div class="info custom-block"><p class="custom-block-title">笔者说</p><p>对于技术的学习，笔者一贯遵循的步骤是：先用最最简单的 demo 让它跑起来，然后学学它的最最常用 API 和 配置让自己能用起来，最后熟练使用的基础上，在空闲时尝试阅读它的源码让自己能够洞彻它的运行机制，部分问题出现的原因，同时借鉴这些技术实现来提升自己的代码高度。</p><p>所以在笔者的文章中，前期基本都是小白文，仅仅穿插很少量的源码研究。当然等小白文更新多了，你们还依然喜欢，后期会不定时专门对部分技术的源码进行解析。</p></div></div></div></main><footer class="VPDocFooter" data-v-53ed897c data-v-f3af8004><!--[--><!--[--><!--[--><!--[--><!----><!--]--><!--]--><!--]--><!--]--><div class="edit-info" data-v-f3af8004><div class="edit-link" data-v-f3af8004><a class="VPLink link vp-external-link-icon no-icon edit-link-button" href="https://github.com/Charles7c/charles7c.github.io/edit/main/docs/courses/mybatis/01-MyBatis基础/04-SQL映射文件之查询元素.md" target="_blank" rel="noreferrer" data-v-f3af8004><!--[--><svg xmlns="http://www.w3.org/2000/svg" viewbox="0 0 24 24" class="edit-link-icon" aria-label="edit icon" data-v-f3af8004><path d="M18,23H4c-1.7,0-3-1.3-3-3V6c0-1.7,1.3-3,3-3h7c0.6,0,1,0.4,1,1s-0.4,1-1,1H4C3.4,5,3,5.4,3,6v14c0,0.6,0.4,1,1,1h14c0.6,0,1-0.4,1-1v-7c0-0.6,0.4-1,1-1s1,0.4,1,1v7C21,21.7,19.7,23,18,23z"></path><path d="M8,17c-0.3,0-0.5-0.1-0.7-0.3C7,16.5,6.9,16.1,7,15.8l1-4c0-0.2,0.1-0.3,0.3-0.5l9.5-9.5c1.2-1.2,3.2-1.2,4.4,0c1.2,1.2,1.2,3.2,0,4.4l-9.5,9.5c-0.1,0.1-0.3,0.2-0.5,0.3l-4,1C8.2,17,8.1,17,8,17zM9.9,12.5l-0.5,2.1l2.1-0.5l9.3-9.3c0.4-0.4,0.4-1.1,0-1.6c-0.4-0.4-1.2-0.4-1.6,0l0,0L9.9,12.5z M18.5,2.5L18.5,2.5L18.5,2.5z"></path></svg> 不妥之处，敬请雅正<!--]--></a></div><div class="last-updated" data-v-f3af8004><p class="VPLastUpdated" data-v-f3af8004 data-v-a25eb6f3>最后更新: <time datetime="2022-08-13T15:30:56.000Z" data-v-a25eb6f3></time></p></div></div><nav class="prev-next" data-v-f3af8004><div class="pager" data-v-f3af8004><a class="VPLink link pager-link prev" href="/courses/mybatis/01-MyBatis%E5%9F%BA%E7%A1%80/03-%E6%A0%B8%E5%BF%83%E9%85%8D%E7%BD%AE%E6%96%87%E4%BB%B6" data-v-f3af8004><!--[--><span class="desc" data-v-f3af8004>上一篇</span><span class="title" data-v-f3af8004><div class="text-color-yellow mr-[6px]" style="font-weight: 550; display: inline-block;">3</div>核心配置文件</span><!--]--></a></div><div class="pager" data-v-f3af8004><a class="VPLink link pager-link next" href="/courses/mybatis/01-MyBatis%E5%9F%BA%E7%A1%80/05-SQL%E6%98%A0%E5%B0%84%E6%96%87%E4%BB%B6%E4%B9%8B%E5%A2%9E%E5%88%A0%E6%94%B9%E5%85%83%E7%B4%A0" data-v-f3af8004><!--[--><span class="desc" data-v-f3af8004>下一篇</span><span class="title" data-v-f3af8004><div class="text-color-gray mr-[6px]" style="font-weight: 550; display: inline-block;">5</div>SQL映射文件之增删改元素</span><!--]--></a></div></nav></footer><!--[--><!--[--><!--[--><div id="comment-container"></div><!--]--><!--]--><!--]--></div></div></div><!--[--><!--]--></div></div><!----><!--[--><!--]--></div></div>
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class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/tiger.svg\\\" title=\\\"虎年\\\" alt=\\\"生肖\\\">\\n 2022年 (12篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>解决 Maven 传递依赖污染的问题\",\"link\":\"/categories/issues/2022/11/23/解决Maven传递依赖污染的问题\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>解决 DotNet 安装完，报错：Couldn't find a valid ICU package installed on the system. Please install libicu using your package manager and try again\",\"link\":\"/categories/issues/2022/11/06/解决DotNET安装后报错的问题\"},{\"text\":\"<div class=\\\"text-color-yellow mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">3</div>解决 Docker 安装 Prometheus 启动报 permission denied 的问题\",\"link\":\"/categories/issues/2022/11/04/解决Docker安装Prometheus启动报错的问题\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">4</div>Docker 设置网络代理\",\"link\":\"/categories/issues/2022/10/29/Docker设置网络代理\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">5</div>解决 CentOS 8 执行 yum install 报 Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist 的问题\",\"link\":\"/categories/issues/2022/10/25/解决CentOS8执行yum安装报错\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">6</div>解决 Windows 桌面部分快捷方式图标变为空白的问题\",\"link\":\"/categories/issues/2022/10/15/解决Windows桌面部分快捷方式图标变为空白的问题\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">7</div>解决无法重复读取请求体和响应体的问题\",\"link\":\"/categories/issues/2022/09/23/解决无法重复读取请求体和响应体的问题\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">8</div>Nginx转发请求，报13：Permission denied错误\",\"link\":\"/categories/issues/2022/09/05/Nginx转发请求，报13：Permission denied错误\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">9</div>SpringBoot项目引入OpenFeign后无法启动\",\"link\":\"/categories/issues/2022/08/31/SpringBoot项目引入OpenFeign后无法启动\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">10</div>执行Shell脚本，报java: command not found\",\"link\":\"/categories/issues/2022/08/11/执行Shell脚本，报java command not found\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">11</div>创建一个自身类的静态对象变量，究竟会如何执行？\",\"link\":\"/categories/issues/2022/03/24/创建一个自身类的静态对象变量，究竟会如何执行？\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">12</div>JavaScript 无法存储 Java Long 类型数据问题\",\"link\":\"/categories/issues/2022/01/26/JavaScript 无法存储 Java Long 类型数据问题\"}],\"collapsed\":false},{\"text\":\"<img class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/ox.svg\\\" title=\\\"牛年\\\" alt=\\\"生肖\\\">\\n 2021年 (5篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>无法访问 F:\\\\。文件或目录损坏且无法读取。\",\"link\":\"/categories/issues/2021/12/13/无法访问F盘。文件或目录损坏且无法读取\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>SQL 注入攻击风险\",\"link\":\"/categories/issues/2021/12/11/SQL 注入攻击风险\"},{\"text\":\"<div class=\\\"text-color-yellow mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">3</div>Command line is too long. Shorten command line for XXX or also for Spring Boot default configuration？\",\"link\":\"/categories/issues/2021/12/10/Command line is too long. 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display: inline-block;\\\">1</div>个人常用快捷键\",\"link\":\"/categories/fragments/2022/10/06/个人常用快捷键\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>个人常用 Git 命令\",\"link\":\"/categories/fragments/2022/10/05/个人常用Git命令\"},{\"text\":\"<div class=\\\"text-color-yellow mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">3</div>个人常用 Docker 命令\",\"link\":\"/categories/fragments/2022/10/01/个人常用Docker命令\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">4</div>个人常用 SQL 函数\",\"link\":\"/categories/fragments/2022/02/16/个人常用SQL函数\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">5</div>个人常用 Linux 命令\",\"link\":\"/categories/fragments/2019/12/31/个人常用Linux命令\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">6</div>个人常用 Hutool 工具类\",\"link\":\"/categories/fragments/2019/12/30/个人常用Hutool工具类\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">7</div>个人常用 Stream 使用技巧\",\"link\":\"/categories/fragments/2019/12/29/个人常用Stream使用技巧\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">8</div>个人 SQL 优化技巧\",\"link\":\"/categories/fragments/2019/12/28/个人SQL优化技巧\"}],\"collapsed\":false},{\"text\":\"<img class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/rabbit.svg\\\" title=\\\"兔年\\\" alt=\\\"生肖\\\">\\n 2023年 (1篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>阿里巴巴的Code Review方法论与实践总结\",\"link\":\"/categories/fragments/2023/01/06/CodeReview方法论与实践总结\"}],\"collapsed\":false},{\"text\":\"<img class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/tiger.svg\\\" title=\\\"虎年\\\" alt=\\\"生肖\\\">\\n 2022年 (15篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>简单聊聊如何让网站开启灰色显示\",\"link\":\"/categories/fragments/2022/12/07/网站开启灰色显示\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>使用 IntelliJ IDEA 进行远程程序调试\",\"link\":\"/categories/fragments/2022/11/01/使用IDEA进行远程程序调试\"},{\"text\":\"<div class=\\\"text-color-yellow mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">3</div>CentOS 安装 Docker、Docker Compose\",\"link\":\"/categories/fragments/2022/10/31/CentOS安装Docker\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">4</div>Docker 安装 MinIO 详细步骤\",\"link\":\"/categories/fragments/2022/10/28/Docker安装MinIO\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">5</div>Docker 安装 Consul 详细步骤\",\"link\":\"/categories/fragments/2022/10/27/Docker安装Consul\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">6</div>Docker 安装 OpenLDAP 详细步骤\",\"link\":\"/categories/fragments/2022/10/26/Docker安装OpenLDAP\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">7</div>个人常用快捷键\",\"link\":\"/categories/fragments/2022/10/06/个人常用快捷键\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">8</div>个人常用 Git 命令\",\"link\":\"/categories/fragments/2022/10/05/个人常用Git命令\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">9</div>个人常用 Docker 命令\",\"link\":\"/categories/fragments/2022/10/01/个人常用Docker命令\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">10</div>内网CentOS服务器设置网络代理\",\"link\":\"/categories/fragments/2022/08/29/内网CentOS服务器设置网络代理\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">11</div>为指定Git仓库单独配置用户名和邮箱\",\"link\":\"/categories/fragments/2022/03/28/为指定Git仓库单独配置用户名和邮箱\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">12</div>修改Git所有提交记录中的作者和邮箱\",\"link\":\"/categories/fragments/2022/03/27/修改Git所有提交记录中的作者和邮箱\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">13</div>修改Git最后一次提交记录的作者和邮箱\",\"link\":\"/categories/fragments/2022/03/26/修改Git最后一次提交记录的作者和邮箱\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">14</div>合并两个Git仓库的历史提交记录\",\"link\":\"/categories/fragments/2022/03/25/合并两个Git仓库的历史提交记录\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">15</div>个人常用 SQL 函数\",\"link\":\"/categories/fragments/2022/02/16/个人常用SQL函数\"}],\"collapsed\":true},{\"text\":\"<img class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/ox.svg\\\" title=\\\"牛年\\\" alt=\\\"生肖\\\">\\n 2021年 (2篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>设计模式之单例模式\",\"link\":\"/categories/fragments/2021/05/29/设计模式之单例模式\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>精密计算工具类-BigDecimal\",\"link\":\"/categories/fragments/2021/03/12/精密计算工具类-BigDecimal\"}],\"collapsed\":true},{\"text\":\"<img class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/pig.svg\\\" title=\\\"猪年\\\" alt=\\\"生肖\\\">\\n 2019年 (4篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>个人常用 Linux 命令\",\"link\":\"/categories/fragments/2019/12/31/个人常用Linux命令\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>个人常用 Hutool 工具类\",\"link\":\"/categories/fragments/2019/12/30/个人常用Hutool工具类\"},{\"text\":\"<div class=\\\"text-color-yellow mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">3</div>个人常用 Stream 使用技巧\",\"link\":\"/categories/fragments/2019/12/29/个人常用Stream使用技巧\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">4</div>个人 SQL 优化技巧\",\"link\":\"/categories/fragments/2019/12/28/个人SQL优化技巧\"}],\"collapsed\":true}],\"/categories/solutions/\":[{\"text\":\"<img class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/tiger.svg\\\" title=\\\"虎年\\\" alt=\\\"生肖\\\">\\n 2022年 (1篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>递归查询树型结构数据的性能优化方案\",\"link\":\"/categories/solutions/2022/09/07/递归查询树型结构数据的性能优化方案\"}],\"collapsed\":false},{\"text\":\"<img class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/ox.svg\\\" title=\\\"牛年\\\" alt=\\\"生肖\\\">\\n 2021年 (2篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>一条SQL查询今年每月统计信息\",\"link\":\"/categories/solutions/2021/11/22/一条SQL查询今年每月统计信息\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>用Java8获取近N天日期\",\"link\":\"/categories/solutions/2021/11/18/用Java8获取近N天日期\"}],\"collapsed\":true}],\"/categories/tools/\":[{\"text\":\"<img class=\\\"chinese-zodiac\\\" style=\\\"position: static; vertical-align: middle; padding-bottom: 3px;\\\" src=\\\"/img/svg/chinese-zodiac/ox.svg\\\" title=\\\"牛年\\\" alt=\\\"生肖\\\">\\n 2021年 (5篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>Quartz 快速入门\",\"link\":\"/categories/tools/2021/03/10/Quartz快速入门\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>Postman 快速入门\",\"link\":\"/categories/tools/2021/03/06/Postman快速入门\"},{\"text\":\"<div class=\\\"text-color-yellow mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">3</div>Another Redis Desktop Manager 快速入门\",\"link\":\"/categories/tools/2021/03/04/ARDM快速入门\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">4</div>Redis Desktop Manager 快速入门\",\"link\":\"/categories/tools/2021/02/22/RDM快速入门\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">5</div>初识 Lombok\",\"link\":\"/categories/tools/2021/01/14/初识Lombok\"}],\"collapsed\":false}],\"/courses/java/\":[{\"text\":\"Java语法入门 (14篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>开发环境搭建\",\"link\":\"/courses/java/01-Java语法入门/01-开发环境搭建\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>第一个Java程序\",\"link\":\"/courses/java/01-Java语法入门/02-第一个Java程序\"},{\"text\":\"<div class=\\\"text-color-yellow mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">3</div>初识Eclipse\",\"link\":\"/courses/java/01-Java语法入门/03-初识Eclipse\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">4</div>程序和计算机的那点事儿\",\"link\":\"/courses/java/01-Java语法入门/04-程序和计算机的那点事儿\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">5</div>变量和常量\",\"link\":\"/courses/java/01-Java语法入门/05-变量和常量\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">6</div>常用的运算符\",\"link\":\"/courses/java/01-Java语法入门/06-常用的运算符\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">7</div>控制语句和流程图\",\"link\":\"/courses/java/01-Java语法入门/07-控制语句和流程图\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">8</div>if选择结构\",\"link\":\"/courses/java/01-Java语法入门/08-if选择结构\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; 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display: inline-block;\\\">1</div>类和对象\",\"link\":\"/courses/java/02-Java面向对象/01-类和对象\"}],\"collapsed\":true},{\"text\":\"Java高级特性 (1篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>集合与泛型-1\",\"link\":\"/courses/java/03-Java高级特性/01-集合与泛型-1\"}],\"collapsed\":true},{\"text\":\"附录 (1篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>CentOS 8.2 安装 JDK 1.8.0_202\",\"link\":\"/courses/java/04-附录/01-CentOS安装JDK\"}],\"collapsed\":true}],\"/courses/mysql/\":[{\"text\":\"MySQL基础 (1篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>MySQL安装与配置\",\"link\":\"/courses/mysql/01-MySQL基础/01-MySQL安装与配置\"}],\"collapsed\":true},{\"text\":\"附录 (2篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>CentOS 8.2 安装 MySQL 5.7.39\",\"link\":\"/courses/mysql/03-附录/01-CentOS安装MySQL\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>Docker 安装 MySQL 详细步骤\",\"link\":\"/courses/mysql/03-附录/02-Docker安装MySQL\"}],\"collapsed\":false}],\"/courses/mybatis/\":[{\"text\":\"MyBatis基础 (8篇)\",\"items\":[{\"text\":\"<div class=\\\"text-color-red mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">1</div>快速入门\",\"link\":\"/courses/mybatis/01-MyBatis基础/01-快速入门\"},{\"text\":\"<div class=\\\"text-color-orange mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">2</div>核心对象\",\"link\":\"/courses/mybatis/01-MyBatis基础/02-核心对象\"},{\"text\":\"<div class=\\\"text-color-yellow mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">3</div>核心配置文件\",\"link\":\"/courses/mybatis/01-MyBatis基础/03-核心配置文件\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; display: inline-block;\\\">4</div>SQL映射文件之查询元素\",\"link\":\"/courses/mybatis/01-MyBatis基础/04-SQL映射文件之查询元素\"},{\"text\":\"<div class=\\\"text-color-gray mr-[6px]\\\" style=\\\"font-weight: 550; 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