vitepress-theme-blog-charles7c-s1/assets/courses_mybatis_02-MyBatis-Plus基础_03-简单查询操作.md.OO_paHtp.js

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to &quot;前言&quot;">​</a></h2><p><strong>C：</strong> 在 CRUD 中，哪一个操作是最复杂的，毫无疑问是 R（查询）操作。在大多数业务中，查询也是涉及最广泛的部分。很多初级程序员有个毛病：简单的查询不想写，难一点的查询不会写。</p><p>上一篇，我们体验了 MP 的增删改操作，本篇，笔者将带你看看你想写或不想写的查询究竟被 MP 封装优化成什么样了。</p><p><img src="'+F+'" alt="202101231220866"></p><h2 id="数据准备" tabindex="-1">数据准备 <a class="header-anchor" href="#数据准备" aria-label="Permalink to &quot;数据准备&quot;">​</a></h2><p>在介绍查询操作前，我们需要重置一次数据表，因为上一篇，数据表的数据已经被我们玩的不能看了。</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;">-- 清空用户表数据</span></span>\n<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">TRUNCATE</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> TABLE</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> user;</span></span>\n<span class="line"></span>\n<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">-- 向用户表插入测试数据</span></span>\n<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">INSERT INTO</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;"> `user`</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> VALUES</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Jone&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">18</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Jone@126.com&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>\n<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">INSERT INTO</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;"> `user`</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> VALUES</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Jack&#39;</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 style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Jack@126.com&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>\n<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">INSERT INTO</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;"> `user`</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> VALUES</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">3</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Tom&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">28</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Tom@126.com&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>\n<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">INSERT INTO</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;"> `user`</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> VALUES</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">4</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Sandy&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">21</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Sandy@126.com&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>\n<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">INSERT INTO</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;"> `user`</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> VALUES</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Billie&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">24</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&#39;Billie@126.com&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">NOW</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(), </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span></code></pre></div><p><img src="'+B+`" alt="202101231220888"></p><h2 id="根据id查询记录" tabindex="-1">根据ID查询记录 <a class="header-anchor" href="#根据id查询记录" aria-label="Permalink to &quot;根据ID查询记录&quot;">​</a></h2><p>在MP 的 BaseMapper 中，为我们提供了 10 来个查询操作，我们还是先介绍一些简单的 API，至于需要使用条件构造器的 API 等等再说。</p><p>那第1个要介绍的查询操作是：根据 ID 查询单个实体数据，日常开发中将会频繁使用的一个 API。</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:#6A737D;--shiki-dark:#768390;">// 其他 API 略</span></span>
<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;"> BaseMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> Mapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">    </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;">     * 根据 ID 查询</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;">     * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> id</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 主键ID</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;"> 单个实体数据</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;">    T </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectById</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(Serializable </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">id</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></code></pre></div><p>接下来，我们准备测试一下它，我们还是先在上一篇 Demo 项目的基础上，复制粘贴一个专门用于测试 R 操作的单元测试类。</p><p><img src="`+c+`" alt="202101231221195"></p><p><strong>测试代码：</strong></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:#24292E;--shiki-dark:#ADBAC7;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SpringBootTest</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> MybatisPlusRTests</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 style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Autowired</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">    private</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper;</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;"> testSelectById</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 查询ID为1的用户数据</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:#24292E;--shiki-dark:#ADBAC7;"> userMapper.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectById</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">5L</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        System.out.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">println</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(user);</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 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:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">  Preparing: </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SELECT</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> id,</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">,age,email,create_time,update_time,is_delete </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:#24292E;--shiki-dark:#ADBAC7;"> id</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</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;"> is_delete</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> Parameters: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(Long)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">    Columns: id, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, age, email, create_time, update_time, is_delete</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">        Row</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jone, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">18</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jone@126.com, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">      Total: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</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, createTime=2021-01-23T17:47:52, updateTime=2021-01-23T17:47:52, isDelete=0)</span></span></code></pre></div><div class="tip custom-block"><p class="custom-block-title">笔者说</p><p>在控制台上显示的执行 SQL 中，我们可以看到它结尾有一个 <code>is_delete = 0</code> 条件，别害怕，这是我们上一篇配置逻辑删除后的正常现象。</p></div><h2 id="批量id查询" tabindex="-1">批量ID查询 <a class="header-anchor" href="#批量id查询" aria-label="Permalink to &quot;批量ID查询&quot;">​</a></h2><p>第2个要介绍的查询操作是：根据多个 ID 来批量查询实体数据。</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:#6A737D;--shiki-dark:#768390;">// 其他 API 略</span></span>
<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;"> BaseMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> Mapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; {</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;">     * 查询（根据ID 批量查询）</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;">     * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> idList</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 主键ID列表(不能为 null 以及 empty)</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;"> 实体列表</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&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectBatchIds</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;">(Constants.COLLECTION) Collection&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">?</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> extends</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> Serializable</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">idList</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></code></pre></div><p><strong>测试代码：</strong></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:#24292E;--shiki-dark:#ADBAC7;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SpringBootTest</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> MybatisPlusRTests</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 style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Autowired</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">    private</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper;</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;">    public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> void</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;"> selectBatchIds</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 查询ID为1、2的用户数据</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        List</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">&gt; </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">users</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;">selectBatchIds</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(Arrays.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">asList</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">));</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        users.</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>
<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></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:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">  Preparing: </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SELECT</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> id,</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">,age,email,create_time,update_time,is_delete </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:#24292E;--shiki-dark:#ADBAC7;"> id </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">IN</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;"> is_delete</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> Parameters: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Integer</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">), </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Integer</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">    Columns: id, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, age, email, create_time, update_time, is_delete</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">        Row</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jone, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">18</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jone@126.com, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">        Row</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jack, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jack@126.com, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">      Total: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</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, createTime=2021-01-23T17:47:52, updateTime=2021-01-23T17:47:52, isDelete=0)</span></span>
<span class="line"><span>User(id=2, name=Jack, age=20, email=Jack@126.com, createTime=2021-01-23T17:47:52, updateTime=2021-01-23T17:47:52, isDelete=0)</span></span></code></pre></div><h2 id="简单的带条件查询" tabindex="-1">简单的带条件查询 <a class="header-anchor" href="#简单的带条件查询" aria-label="Permalink to &quot;简单的带条件查询&quot;">​</a></h2><p>第3个要介绍的查询操作是：根据 Map 集合封装好的条件来查询实体列表。</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:#6A737D;--shiki-dark:#768390;">// 其他 API 略</span></span>
<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;"> BaseMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> Mapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; {</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;">     * 查询（根据 columnMap 条件）</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;">     * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> columnMap</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 表字段 map 对象</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;"> 实体列表</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&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectByMap</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;">(Constants.COLUMN_MAP) Map&lt;</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;">&gt; </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">columnMap</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></code></pre></div><p><strong>测试代码：</strong></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:#24292E;--shiki-dark:#ADBAC7;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SpringBootTest</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> MybatisPlusRTests</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 style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Autowired</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">    private</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper;</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;"> selectByMap</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 通过 Map 封装条件</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // Map集合的键表示的是数据库列名</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        HashMap</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">&lt;</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;">&gt; </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">columnMap</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&lt;&gt;();</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        columnMap.</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;">&quot;name&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&quot;Jack&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        columnMap.</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;">&quot;age&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&quot;20&quot;</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:#6A737D;--shiki-dark:#768390;">        // 根据条件查询用户列表</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        List</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">&gt; </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">users</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;">(columnMap);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        users.</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>
<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></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:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">  Preparing: </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SELECT</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> id,</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">,age,email,create_time,update_time,is_delete </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;"> =</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 style="--shiki-light:#D73A49;--shiki-dark:#F47067;">AND</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> is_delete</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> Parameters: Jack(String), </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(String)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">    Columns: id, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, age, email, create_time, update_time, is_delete</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">        Row</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jack, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jack@126.com, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">      Total: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</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, createTime=2021-01-23T17:47:52, updateTime=2021-01-23T17:47:52, isDelete=0)</span></span></code></pre></div><h2 id="分页" tabindex="-1">分页 <a class="header-anchor" href="#分页" aria-label="Permalink to &quot;分页&quot;">​</a></h2><p>在大多数批量查询操作的时候，我们都会采用分页技术来限制查询的条数，以优化效率及体验。</p><p>所以第4个要介绍的查询操作就是分页查询，原来在使用 MyBatis 时，接入 <a href="https://pagehelper.github.io/" target="_blank" rel="noreferrer">page-helper</a> 就可以快速实现分页功能，而 MP 则自带分页插件，只要简单的配置就可以实现分页功能。</p><p><strong>在项目中创建一个 MP 配置类，添加一个分页插件类的 Bean 配置。</strong></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:#6A737D;--shiki-dark:#768390;">/**</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> * MyBatis Plus配置类</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;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Configuration</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> MyBatisPlusConfig</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 style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Bean</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">    public</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> PaginationInterceptor </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">paginationInterceptor</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        PaginationInterceptor</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> paginationInterceptor</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;"> PaginationInterceptor</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">();</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 设置请求的页面大于最大页后操作， true调回到首页，false 继续请求  默认false</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // paginationInterceptor.setOverflow(false);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        </span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 设置最大单页限制数量，默认 500 条，-1 不受限制</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // paginationInterceptor.setLimit(500);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        </span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 开启 count 的 join 优化,只针对部分 left join</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        paginationInterceptor.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">setCountSqlParser</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">new</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;"> JsqlParserCountOptimize</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">true</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">));</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">        return</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> paginationInterceptor;</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 style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">}</span></span></code></pre></div><p>好了，接下来我们就可以测试分页查询 API 了。</p><p>在 BaseMapper 中，一共提供了两种分页查询，它们都可以实现分页数据的查询，<strong>唯一的区别在于查到的每页数据，究竟是要存储为实体数据集合，还是直接以键值对形式存到Map集合。</strong></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:#6A737D;--shiki-dark:#768390;">// 其他 API 略</span></span>
<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;"> BaseMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#6CB6FF;"> Mapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">    </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;">     * 根据 entity 条件，查询全部记录（并翻页）</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;">     * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> page</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">         分页查询条件（可以为 RowBounds.DEFAULT）</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;"> queryWrapper</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 实体对象封装操作类（可以为 null）</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;"> 分页数据（查询到的每页数据会映射为实体数据集合）</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;">    &lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">E</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> extends</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> IPage&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt;&gt; E </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectPage</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(E </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">page</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;">(Constants.WRAPPER) Wrapper&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">queryWrapper</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:#6A737D;--shiki-dark:#768390;">    /**</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">     * 根据 Wrapper 条件，查询全部记录（并翻页）</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;">     * </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">@param</span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;"> page</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">         分页查询条件</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;"> queryWrapper</span><span style="--shiki-light:#6A737D;--shiki-dark:#768390;"> 实体对象封装操作类</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;"> 分页数据（查询到的每页数据会以键值对形式存入Map集合）</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;">    &lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">E</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> extends</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> IPage&lt;Map&lt;</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;">&gt;&gt;&gt; E </span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectMapsPage</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(E </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">page</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;">(Constants.WRAPPER) Wrapper&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">T</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">&gt; </span><span style="--shiki-light:#E36209;--shiki-dark:#F69D50;">queryWrapper</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>笔者只带大家测试第一种分页查询 API，另一种你可以自行选择测试一下。</p><p><strong>测试代码：</strong></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:#24292E;--shiki-dark:#ADBAC7;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SpringBootTest</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#F69D50;"> MybatisPlusDemoApplication</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 style="--shiki-light:#D73A49;--shiki-dark:#F47067;">Autowired</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">    private</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> UserMapper</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> userMapper;</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;"> testSelectPage</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 创建分页对象，通过构造传入 当前页 和 每页显示条数</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        Page</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">&lt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">User</span><span style="--shiki-light:#24292E;--shiki-dark:#F69D50;">&gt; </span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">page</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;"> Page&lt;&gt;(</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</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:#6A737D;--shiki-dark:#768390;">        // 查询分页数据，条件构造器部分我们还是先传null</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        userMapper.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">selectPage</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(page, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">null</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">);</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 分页数据输出</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        System.out.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">println</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&quot;数据总数:&quot;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> +</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> page.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getTotal</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">());</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        System.out.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">println</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&quot;总页数:&quot;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> +</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> page.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getPages</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">());</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        System.out.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">println</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&quot;当前页:&quot;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> +</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> page.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getCurrent</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">());</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        System.out.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">println</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#96D0FF;">&quot;页大小:&quot;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> +</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> page.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getSize</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">());</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#768390;">        // 每页的数据列表</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">        page.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#DCBDFB;">getRecords</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">().</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>
<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:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">  Preparing: </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SELECT</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> COUNT</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">) </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:#24292E;--shiki-dark:#ADBAC7;"> is_delete </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> Parameters: </span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">    Columns: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">COUNT</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">        Row</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">5</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">  Preparing: </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">SELECT</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> id,</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">,age,email,create_time,update_time,is_delete </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:#24292E;--shiki-dark:#ADBAC7;"> is_delete</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;"> LIMIT</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> ?</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">==&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;"> Parameters: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">(Long)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">    Columns: id, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">name</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, age, email, create_time, update_time, is_delete</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">        Row</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jone, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">18</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jone@126.com, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">        Row</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jack, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, Jack@126.com, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2021</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">01</span><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">-</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">23</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;"> 17</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">47</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">52</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">0</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F47067;">&lt;==</span><span style="--shiki-light:#24292E;--shiki-dark:#ADBAC7;">      Total: </span><span style="--shiki-light:#005CC5;--shiki-dark:#6CB6FF;">2</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>数据总数:5</span></span>
<span class="line"><span>总页数:3</span></span>
<span class="line"><span>当前页:1</span></span>
<span class="line"><span>页大小:2</span></span>
<span class="line"><span>User(id=1, name=Jone, age=18, email=Jone@126.com, createTime=2021-01-23T17:47:52, updateTime=2021-01-23T17:47:52, isDelete=0)</span></span>
<span class="line"><span>User(id=2, name=Jack, age=20, email=Jack@126.com, createTime=2021-01-23T17:47:52, updateTime=2021-01-23T17:47:52, isDelete=0)</span></span></code></pre></div><div class="tip custom-block"><p class="custom-block-title">笔者说</p><p>测试完后，笔者再告诉你一件事儿，MP 的这款分页插件，支持的数据库也很多： MySQL 、MariaDB 、Oracle 、DB2 、H2 、HSQL 、SQL Lite 、PostgreSQL 、SQL Server 、Presto 、Gauss 、Firebird、Phoenix 、ClickHouse 、Sybase ASE 、 OceanBase 、达梦数据库 、虚谷数据库 、人大金仓数据库 、南大通用数据库。</p><p>这么多种类的数据库支持，从我们日常使用上来讲绝对够用了！</p></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 &quot;参考文献&quot;">​</a></h2><p>[1]MyBatis Plus 官网. 指南[EB/OL]. <a href="https://baomidou.com/guide/" target="_blank" rel="noreferrer">https://baomidou.com/guide/</a>. 2021-01-18</p><h2 id="后记" tabindex="-1">后记 <a class="header-anchor" href="#后记" aria-label="Permalink to &quot;后记&quot;">​</a></h2><p><strong>C：</strong> 好了，简单的查询操作就介绍到这儿了，这些基础查询是不是还挺简单的？下一篇，我们将介绍预热了两篇已久的条件构造器，肯定有很多同学等急了。别着急，好饭不怕晚，下一篇笔者就带你好好认识认识它。</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>`,56);function m(s,v,b,T,_,P){const k=l,p=e("ClientOnly");return n(),r("div",null,[E,d(p,null,{default:g(()=>{var i,a;return[(((i=s.$frontmatter)==null?void 0:i.aside)??!0)&&(((a=s.$frontmatter)==null?void 0:a.showArticleMetadata)??!0)?(n(),C(k,{key:0,article:s.$frontmatter},null,8,["article"])):D("",!0)]}),_:1}),u])}const f=t(o,[["render",m]]);export{q as __pageData,f as default};