diff options
Diffstat (limited to '2025/04/02/N-1-selects-problem-与-Prisma-ORM')
| -rw-r--r-- | 2025/04/02/N-1-selects-problem-与-Prisma-ORM/index.html | 291 |
1 files changed, 291 insertions, 0 deletions
diff --git a/2025/04/02/N-1-selects-problem-与-Prisma-ORM/index.html b/2025/04/02/N-1-selects-problem-与-Prisma-ORM/index.html new file mode 100644 index 00000000..18320f16 --- /dev/null +++ b/2025/04/02/N-1-selects-problem-与-Prisma-ORM/index.html @@ -0,0 +1,291 @@ +<!DOCTYPE html> +<html lang="en"> + <head> + <meta charset="UTF-8"> +<meta name="viewport" + content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0"> +<meta http-equiv="X-UA-Compatible" content="ie=edge"> + + <meta name="author" content="韩暮秋"> + + + <meta name="subtitle" content="暮秋小屋"> + + + <meta name="description" content="这里是暮秋小屋，思念和灵感的寄存处"> + + + <meta name="keywords" content="韩暮秋,MuqiuHan,'Muqiu Han', 'muqiu han', muqiuhan"> + + + + +<title>N+1 selects problem 与 Prisma ORM | 暮秋小屋</title> + + + + <link rel="icon" href="/favicon.ico"> + + + +<style> + @import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=Noto+Sans+SC:wght@300;400;500;700&family=Roboto+Mono&display=swap'); +</style> + + + + <!-- stylesheets list from _config.yml --> + + <link rel="stylesheet" href="/css/style.css"> + + + + + + <!-- scripts list from _config.yml --> + + <script src="/js/frame.js"></script> + + + + + + <script src="https://polyfill.alicdn.com/polyfill.js?features=es6"></script> + <script id="MathJax-script" async src="https://lf6-cdn-tos.bytecdntp.com/cdn/expire-1-M/mathjax/3.2.0/es5/tex-mml-chtml.js"></script> + + + + + + + + <meta name="generator" content="Hexo 6.3.0"></head> + <body> + <div class="mask-border"> + </div> + + <div class="wrapper"> + + <div class="header"> + <div class="flex-container"> + <div class="header-inner"> + <div class="site-brand-container"> + <a href="/"> + + 暮秋小屋 + + </a> + </div> + <div id="menu-btn" class="menu-btn" onclick="toggleMenu()"> + Menu + </div> + <nav class="site-nav"> + <ul class="menu-list"> + + + <li class="menu-item"> + <a href="/">主页</a> + </li> + + + + <li class="menu-item"> + <a href="/categories/gallery/">日记本</a> + </li> + + + + <li class="menu-item"> + <a href="/tags/Medicine/">医学</a> + </li> + + + + <li class="menu-item"> + <a href="/tags/Technique/">计算机科学</a> + </li> + + + + <li class="menu-item"> + <a href="/tags/Life/">生活</a> + </li> + + + + <li class="menu-item"> + <a href="/about">关于</a> + </li> + + + + <li class="menu-item search-btn"> + <a href="#">Search</a> + </li> + + </ul> + </nav> + </div> + </div> +</div> +<script src="/js/menu.js"></script> + + + <div class="main"> + <div class="flex-container"> + <article id="post"> + + + <div class="post-head"> + <div class="post-info"> + <div class="tag-list"> + + + <span class="post-tag"> + <a href="/tags/Technique/"> + Technique + </a> + </span> + + + </div> + <div class="post-title"> + + + N+1 selects problem 与 Prisma ORM + + + </div> + <span class="post-date"> + Apr 2, 2025 + </span> + </div> + <div class="post-img"> + + <div class="h-line-primary"></div> + + </div> +</div> + <div class="post-content"> + <p>N+1 查询问题是指在通过 ORM 查询数据时，执行了<strong>一次</strong>初始查询来获取父对象列表（这 <strong>1</strong> 次查询），然后为列表中的<strong>每一个</strong>父对象都单独执行了一次额外的查询来获取其关联的子对象（这 <strong>N</strong> 次查询）。最终导致总共执行了 <strong>1 + N</strong> 次数据库查询，其中 N 是初始查询返回的父对象的数量。</p> +<p><strong>举个例子：</strong></p> +<p>假设有两个数据库模型：<code>User</code>（用户）和 <code>Post</code>（帖子），一个用户可以有多篇帖子（一对多关系）。</p> +<p>现在，需要获取前 10 个用户以及他们各自的所有帖子。</p> +<p>一种<strong>有问题</strong>的 ORM 实现（或不当的使用方式）可能会这样执行：</p> +<ol> +<li><strong>第一次查询 (The “1”)</strong>: 获取前 10 个用户。<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> <span class="keyword">User</span> LIMIT <span class="number">10</span>;</span><br></pre></td></tr></table></figure></li> +<li><strong>接下来的 N (=10) 次查询 (The “N”)</strong>: 对于上一步获取到的每一个用户，单独执行一次查询来获取该用户的帖子。<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">-- 用户 1</span></span><br><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> Post <span class="keyword">WHERE</span> authorId <span class="operator">=</span> <span class="number">1</span>;</span><br><span class="line"><span class="comment">-- 用户 2</span></span><br><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> Post <span class="keyword">WHERE</span> authorId <span class="operator">=</span> <span class="number">2</span>;</span><br><span class="line"><span class="comment">-- 用户 3</span></span><br><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> Post <span class="keyword">WHERE</span> authorId <span class="operator">=</span> <span class="number">3</span>;</span><br><span class="line"><span class="comment">-- ... 直到 用户 10</span></span><br><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> Post <span class="keyword">WHERE</span> authorId <span class="operator">=</span> <span class="number">10</span>;</span><br></pre></td></tr></table></figure></li> +</ol> +<p>在这个场景下，总共执行了 1 + 10 = <strong>11</strong> 次数据库查询。如果 N 的值很大（比如获取 1000 个用户），就会产生 1001 次查询，这对数据库造成巨大的、不必要的压力，并显著增加应用程序的响应时间。每一次数据库交互都有网络延迟和数据库处理的开销，N+1 次查询会将这些开销放大 N 倍。</p> +<p>N+1 问题通常源于 ORM 处理关联数据的方式，特别是与“懒加载”（Lazy Loading）相关的策略。懒加载是指只有在显式访问关联属性时，ORM 才会去数据库加载这些数据。虽然这在某些情况下可以避免加载不需要的数据，但如果在循环中访问关联属性，就很容易触发 N+1 问题。</p> +<p>然而，问题的根源在于<strong>没有有效地预先加载（或批量加载）所需的关联数据</strong>。即使不使用严格意义上的懒加载，如果 ORM 在处理关联查询时不够智能，采用了逐个获取关联对象的策略，同样会产生 N+1 查询。</p> +<p>在 Prisma 出现之前或在其他 ORM 中，解决 N+1 问题常见的方法包括：</p> +<ol> +<li><strong>预先加载（Eager Loading）</strong>: 在执行初始查询时，就明确指示 ORM 同时将关联数据也查询出来。这通常通过 SQL 的 <code>JOIN</code> 操作实现。例如，一次性查询出用户和他们的帖子。虽然这减少了查询次数，但复杂的 <code>JOIN</code> 可能会导致查询本身变得庞大和低效，并可能返回冗余数据。</li> +<li><strong>批量加载（Batch Loading）</strong>: 先执行初始查询获取父对象列表，然后收集所有父对象的 ID，在第二次查询中使用 <code>WHERE IN (...)</code> 子句一次性加载所有相关的子对象。这种方式通常需要两次查询，但避免了 N 次单独的查询。</li> +</ol> +<p>Prisma ORM 在设计上就考虑了 N+1 问题，并提供了一种既方便开发者又高效的解决方案。当使用 Prisma Client 查询数据并需要包含关联模型时，Prisma 会自动优化查询，<strong>避免产生 N+1 查询</strong>，主要通过<strong>关系查询（Relation Queries）</strong>中的 <code>include</code> 选项或嵌套读取（nested reads）来实现这一点：</p> +<p>假设想获取所有用户及其发布的帖子，使用 Prisma Client，可以这样写：</p> +<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">PrismaClient</span> } <span class="keyword">from</span> <span class="string">'@prisma/client'</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> prisma = <span class="keyword">new</span> <span class="title class_">PrismaClient</span>()</span><br><span class="line"></span><br><span class="line"><span class="keyword">async</span> <span class="keyword">function</span> <span class="title function_">getUsersWithPosts</span>(<span class="params"></span>) {</span><br><span class="line"> <span class="keyword">const</span> usersWithPosts = <span class="keyword">await</span> prisma.<span class="property">user</span>.<span class="title function_">findMany</span>({</span><br><span class="line"> <span class="attr">include</span>: {</span><br><span class="line"> <span class="attr">posts</span>: <span class="literal">true</span>, <span class="comment">// 指示 Prisma 加载关联的 posts</span></span><br><span class="line"> },</span><br><span class="line"> })</span><br><span class="line"> <span class="comment">// usersWithPosts 包含了用户列表，每个用户对象中都有一个 posts 数组</span></span><br><span class="line"> <span class="variable language_">console</span>.<span class="title function_">log</span>(usersWithPosts)</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="title function_">getUsersWithPosts</span>()</span><br><span class="line"> .<span class="title function_">catch</span>(<span class="function">(<span class="params">e</span>) =></span> {</span><br><span class="line"> <span class="keyword">throw</span> e</span><br><span class="line"> })</span><br><span class="line"> .<span class="title function_">finally</span>(<span class="keyword">async</span> () => {</span><br><span class="line"> <span class="keyword">await</span> prisma.$disconnect()</span><br><span class="line"> })</span><br></pre></td></tr></table></figure> + +<p>当执行上述查询时，Prisma <strong>不会</strong> 生成 N+1 个 SQL 查询。而是首先会分析请求，并将其转化为数量非常有限的高效 SQL 查询。对于上面这个一对多关系的 <code>include</code> 查询，Prisma 通常会执行以下<strong>两步</strong>（类似于批量加载策略）：</p> +<ol> +<li><strong>查询父模型</strong>: 获取所有 <code>User</code> 记录。<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> "public"."User"."id", "public"."User"."name", <span class="comment">/* ... other user fields */</span> <span class="keyword">FROM</span> "public"."User" <span class="keyword">WHERE</span> <span class="number">1</span><span class="operator">=</span><span class="number">1</span></span><br></pre></td></tr></table></figure></li> +<li><strong>查询关联的子模型</strong>: 使用上一步获取到的所有用户 <code>id</code>，通过 <code>WHERE IN (...)</code> 子句一次性查询所有相关的 <code>Post</code> 记录。<figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">SELECT</span> "public"."Post"."id", "public"."Post"."title", "public"."Post"."authorId", <span class="comment">/* ... other post fields */</span> <span class="keyword">FROM</span> "public"."Post" <span class="keyword">WHERE</span> "public"."Post"."authorId" <span class="keyword">IN</span> ($<span class="number">1</span>, $<span class="number">2</span>, $<span class="number">3</span>, ...) <span class="comment">/* 这里的 $1, $2, ... 是第一步查到的用户 ID 列表 */</span></span><br></pre></td></tr></table></figure></li> +</ol> +<p>Prisma Client 在内存中将这两次查询的结果高效地组合起来，最终返回嵌套的、符合 TypeScript 类型的数据。</p> +<h2 id="Refs"><a href="#Refs" class="headerlink" title="Refs."></a>Refs.</h2><ul> +<li><a target="_blank" rel="noopener" href="https://stackoverflow.com/questions/97197/what-is-the-n1-selects-problem-in-orm-object-relational-mapping">Stack Overflow: What is the N+1 selects problem in ORM?</a></li> +<li><a target="_blank" rel="noopener" href="https://www.prisma.io/docs/orm/prisma-client/queries/query-optimization-performance#solving-the-n1-problem">Prisma Docs: Solving the N+1 problem</a></li> +</ul> + +</div> + +<script> + window.onload = detectors(); +</script> + <div class="post-footer"> + <div class="h-line-primary"></div> + <nav class="post-nav"> + <div class="prev-item"> + + </div> + <div class="next-item"> + + <div class="icon arrow-right"></div> + <div class="post-link"> + <a href="/2025/03/31/%E5%9C%A8F-%E4%B8%AD%E5%A4%84%E7%90%86%E5%A4%8D%E6%9D%82%E4%BE%9D%E8%B5%96%E6%B3%A8%E5%85%A5%E7%9A%84%E5%AE%9E%E8%B7%B5%E6%8C%87%E5%8D%97/">Next</a> + </div> + + </div> + </nav> +</div> + + + <div class="post-comment"> + + + + + + + +</div> + + +</article> + </div> + </div> + + <div class="footer"> + <div class="flex-container"> + <div class="footer-text"> + + + | + + + 希望路过的人可以添点柴火让这里暖和点 + + </div> + </div> +</div> + + </div> + + + <div class="search-popup"> + <div class="search-popup-overlay"> + </div> + <div class="search-popup-window" > + <div class="search-header"> + <div class="search-input-container"> + <input autocomplete="off" autocapitalize="off" maxlength="80" + placeholder="Search Anything" spellcheck="false" + type="search" class="search-input"> + </div> + <div class="search-close-btn"> + <div class="icon close-btn"></div> + </div> + </div> + <div class="search-result-container"> + </div> + </div> +</div> + +<script> + const searchConfig = { + path : "/search.xml", + top_n_per_article: "1", + unescape : "false", + trigger: "auto", + preload: "false" + } +</script> +<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/search.js"></script> +<script src="/js/search.js"></script> + + + + </body> +</html> |