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blog-public/posts/5a4b.html -rw-r--r-- 106.4 KiB
88eebf3d — Cytrogen Deploy 2026-02-19 08:34:27 3 days ago 
                                                                                
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class="container" id="main-content" tabindex="-1"><div class="post"><article class="post-block h-entry"><div class="post-meta p-author h-card visually-hidden"><img class="author-avatar u-photo" src="../favicon.png" alt="Cytrogen"><span class="p-name">Cytrogen</span><a class="u-url" href="https://cytrogen.icu">https://cytrogen.icu</a></div><a class="post-permalink u-url u-uid visually-hidden" href="https://cytrogen.icu/posts/5a4b.html">永久链接</a><div class="p-summary visually-hidden"><p>搭建完前端与后端的基础结构后，我们就可以开始着手于数据库设计了。</p></div><div class="visually-hidden"><a class="p-category" href="../categories/%E7%BC%96%E7%A8%8B%E7%AC%94%E8%AE%B0/">编程笔记</a><a class="p-category" href="../tags/%E5%85%A8%E6%A0%88%E5%AE%9E%E8%B7%B5/">全栈实践</a><a class="p-category" href="../tags/Node-js/">Node.js</a><a class="p-category" href="../tags/React-js/">React.js</a><a class="p-category" href="../tags/TypeScript/">TypeScript</a><a class="p-category" href="../tags/NestJS/">NestJS</a></div><h1 class="post-title p-name">React + NestJS 购物平台练习【3】数据设计与实现</h1><div class="post-info"><time class="post-date dt-published" datetime="2024-11-07T05:00:00.000Z">11/7/2024</time><time class="dt-updated visually-hidden" datetime="2026-02-09T17:16:54.997Z"></time></div><div class="post-content e-content"><html><head></head><body><p>搭建完前端与后端的基础结构后，我们就可以开始着手于数据库设计了。</p>
<span id="more"></span>
<h1 id="1-设计基础实体"><a class="markdownIt-Anchor" href="#1-设计基础实体"></a> 1. 设计基础实体</h1>
<p>在设计我们的购物平台的过程中，实体及其关系是核心的数据模型。我们从业务逻辑的角度来看，每个实体的意义和作用，这样可以更好地理解其在系统中的角色。</p>
<p>这里，我们以「用户」、「商品」、「订单」等为主线，讲解如何建立这些实体以及它们之间的关系，并举例说明其在业务场景中的应用。</p>
<h2 id="11-用户"><a class="markdownIt-Anchor" href="#11-用户"></a> 1.1. 用户</h2>
<p>用户实体是系统的核心，因为大部分操作都需要绑定到用户。每个用户都有其唯一的 ID、用户名、邮箱和密码，这些信息用于身份验证和授权。</p>
<blockquote>
<p>示例，一个用户 <code>John Doe</code> 创建了账号，并通过邮箱 <code>johndoe@example.com</code> 登录系统。数据库会在 <code>Users</code> 表中新增一条记录，保存 John 的邮箱、加密密码和创建时间。</p>
</blockquote>
<h4 id="111-代码实现分析"><a class="markdownIt-Anchor" href="#111-代码实现分析"></a> 1.1.1. 代码实现分析</h4>
<p>让我们深入分析 <code>Users</code> 实体的代码实现：</p>
<figure class="highlight ts"><table><tbody><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><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> {</span><br><span class="line">  <span class="title class_">Entity</span>,</span><br><span class="line">  <span class="title class_">PrimaryGeneratedColumn</span>,</span><br><span class="line">  <span class="title class_">Column</span>,</span><br><span class="line">  <span class="title class_">CreateDateColumn</span>,</span><br><span class="line">  <span class="title class_">UpdateDateColumn</span>,</span><br><span class="line">  <span class="title class_">OneToMany</span>,</span><br><span class="line">  <span class="title class_">OneToOne</span></span><br><span class="line">} <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Users</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>({ <span class="attr">unique</span>: <span class="literal">true</span> })</span><br><span class="line">  <span class="attr">username</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>({ <span class="attr">unique</span>: <span class="literal">true</span> })</span><br><span class="line">  <span class="attr">email</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">password</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@CreateDateColumn</span>()</span><br><span class="line">  <span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@UpdateDateColumn</span>()</span><br><span class="line">  <span class="attr">updated_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p>这部分使用了 TypeORM 的装饰器来定义表结构：</p>
<ul>
<li><code>@Entity()</code> 装饰器将这个类标记为一个数据库实体</li>
<li><code>@PrimaryGeneratedColumn('uuid')</code> 表示自动生成 <code>UUID</code> 作为主键</li>
<li><code>@Column({ unique: true })</code> 为用户名和邮箱添加了唯一性约束，防止重复注册</li>
<li><code>@CreateDateColumn()</code> 会自动记录实体的创建时间</li>
<li><code>@UpdateDateColumn()</code> 会自动记录实体的更新时间</li>
</ul>
<p>用户表的字段及其业务含义如下：</p>
<ul>
<li><code>id</code>：主键，用于唯一标识每个用户，类型为 <code>UUID</code>，确保安全性和唯一性</li>
<li><code>username</code>：用户名，系统中用于显示的名称，通常在用户之间是唯一的</li>
<li><code>email</code>：用户的邮箱，通常作为主要联系手段，同时也是登录的标识之一</li>
<li><code>password</code>：用户密码，以加密方式存储，用于用户验证</li>
<li><code>created_at</code> 和 <code>updated_at</code>：创建时间和更新时间，记录用户注册和资料更新的时间</li>
</ul>
<h4 id="112-关联关系分析"><a class="markdownIt-Anchor" href="#112-关联关系分析"></a> 1.1.2. 关联关系分析</h4>
<p><code>Users</code> 实体与其他实体之间建立了多个关联关系：</p>
<figure class="highlight ts"><table><tbody><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_">Orders</span> } <span class="keyword">from</span> <span class="string">'./orders.entity'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">Carts</span> } <span class="keyword">from</span> <span class="string">'./carts.entity'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">Addresses</span> } <span class="keyword">from</span> <span class="string">'./addresses.entity'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">Payments</span> } <span class="keyword">from</span> <span class="string">'./payments.entity'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Users</span> {</span><br><span class="line">    <span class="comment">// ...</span></span><br><span class="line"></span><br><span class="line">    <span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">Orders</span>, <span class="function"><span class="params">order</span> =&gt;</span> order.<span class="property">user</span>)</span><br><span class="line">    <span class="attr">orders</span>: <span class="title class_">Orders</span>[];</span><br><span class="line"></span><br><span class="line">    <span class="meta">@OneToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Carts</span>, <span class="function"><span class="params">cart</span> =&gt;</span> cart.<span class="property">user</span>)</span><br><span class="line">    <span class="attr">cart</span>: <span class="title class_">Carts</span>;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">Addresses</span>, <span class="function"><span class="params">address</span> =&gt;</span> address.<span class="property">user</span>)</span><br><span class="line">    <span class="attr">addresses</span>: <span class="title class_">Addresses</span>[];</span><br><span class="line"></span><br><span class="line">    <span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">Payments</span>, <span class="function"><span class="params">payment</span> =&gt;</span> payment.<span class="property">user</span>)</span><br><span class="line">    <span class="attr">payments</span>: <span class="title class_">Payments</span>[];</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p>这些关联展示了用户实体在系统中的核心地位：</p>
<ol>
<li>用户 - 订单关系（<code>@OneToMany</code>）
<ul>
<li>一个用户可以有多个订单</li>
<li>这种一对多的关系允许系统追踪用户的所有购买历史</li>
</ul>
</li>
<li>用户 - 购物车关系（<code>@OneToOne</code>）
<ul>
<li>每个用户只能有一个购物车</li>
<li>一对一的关系确保购物车数据的独立性和安全性</li>
</ul>
</li>
<li>用户 - 地址关系（<code>@OneToMany</code>）
<ul>
<li>用户可以保存多个收货地址</li>
<li>方便用户在下单时快速选择收货地址</li>
</ul>
</li>
<li>用户 - 支付关系（<code>@OneToMany</code>）
<ul>
<li>记录用户的所有支付记录</li>
<li>用于追踪交易历史和财务统计</li>
</ul>
</li>
</ol>
<h4 id="113-用户角色"><a class="markdownIt-Anchor" href="#113-用户角色"></a> 1.1.3. 用户角色</h4>
<p>在开发应用程序时，管理用户的权限和访问控制是至关重要的。这是因为不同类型的用户可能需要访问系统的不同功能。</p>
<p>例如，一个购物平台可能有以下几种角色：</p>
<ul>
<li>管理员：可以管理用户、查看所有订单、编辑商品等</li>
<li>普通用户：只能查看商品、下订单、查看个人资料等</li>
<li>游客：仅限浏览，不进行任何交互</li>
</ul>
<p>在这种场景下，我们需要为用户管理系统添加一个角色字段，以便区分不同的用户类型。</p>
<p>角色字段通常有助于完成以下任务：</p>
<ul>
<li>不同权限管理：每种角色都有不同的权限。管理员可能有权访问系统的所有数据，而普通用户只能查看他们自己的数据。通过角色字段，我们可以在数据库中存储每个用户的角色信息</li>
<li>角色控制的用户界面：角色字段可以帮助系统为不同角色的用户显示不同的页面或功能。例如，管理员可以访问管理控制台，而普通用户只能看到他们的订单历史</li>
<li>安全性增强：通过角色字段，系统可以在后端进行权限验证，确保不同角色的用户只能执行允许他们执行的操作，避免了恶意操作或权限滥用</li>
</ul>
<p>为了明确区分不同角色的值，通常我们会使用枚举（<code>enum</code>）来为角色提供固定的值。</p>
<blockquote>
<p><code>enum</code> 是一种特殊的类，用来表示一组固定的常量。</p>
</blockquote>
<p>通过将 <code>role</code> 字段设置为枚举类型，我们可以确保角色值仅限于我们定义的固定值，这些值会自动被 TypeORM 映射到数据库字段中。</p>
<figure class="highlight ts"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="comment">// 添加角色的枚举类型</span></span><br><span class="line"><span class="keyword">export</span> <span class="keyword">enum</span> <span class="title class_">UserRole</span> {</span><br><span class="line">  <span class="variable constant_">ADMIN</span> = <span class="string">'admin'</span>,</span><br><span class="line">  <span class="variable constant_">USER</span> = <span class="string">'user'</span>,</span><br><span class="line">  <span class="variable constant_">GUEST</span> = <span class="string">'guest'</span>,</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Users</span> {</span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line"></span><br><span class="line">  <span class="comment">// 在 Users 实体中添加 role 字段</span></span><br><span class="line">  <span class="meta">@Column</span>({</span><br><span class="line">    <span class="attr">type</span>: <span class="string">'enum'</span>,</span><br><span class="line">    <span class="attr">enum</span>: <span class="title class_">UserRole</span>,</span><br><span class="line">    <span class="attr">default</span>: <span class="title class_">UserRole</span>.<span class="property">USER</span>,  <span class="comment">// 默认值为普通用户</span></span><br><span class="line">  })</span><br><span class="line">  <span class="attr">role</span>: <span class="title class_">UserRole</span>;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<h2 id="12-商品"><a class="markdownIt-Anchor" href="#12-商品"></a> 1.2. 商品</h2>
<p>商品实体是平台中与交易直接相关的核心实体，它承载了商品的基本信息、库存管理、定价等重要功能。一个设计良好的商品实体不仅要满足基本的展示需求，还要支持库存管理、订单处理等复杂业务场景。</p>
<p>商品表的作用是提供系统中可供购买的商品清单，记录商品价格和库存。在库存管理方面，当库存减少到零时，商品需要标记为「缺货」或「下架」。</p>
<blockquote>
<p>示例，商家上架了一款新商品「智能手表」，库存数量为 100，售价为 200 元，商品类别为「电子产品」。这款商品的信息会存储在 <code>Products</code> 表中，供用户选择和购买。</p>
</blockquote>
<h4 id="121-代码实现分析"><a class="markdownIt-Anchor" href="#121-代码实现分析"></a> 1.2.1. 代码实现分析</h4>
<p>让我们详细分析 <code>Products</code> 实体的代码实现：</p>
<figure class="highlight ts"><table><tbody><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><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> {</span><br><span class="line">  <span class="title class_">Entity</span>,</span><br><span class="line">  <span class="title class_">PrimaryGeneratedColumn</span>,</span><br><span class="line">  <span class="title class_">Column</span>,</span><br><span class="line">  <span class="title class_">CreateDateColumn</span>,</span><br><span class="line">  <span class="title class_">UpdateDateColumn</span>,</span><br><span class="line">  <span class="title class_">ManyToOne</span>,</span><br><span class="line">  <span class="title class_">OneToMany</span></span><br><span class="line">} <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Products</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">name</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>(<span class="string">'text'</span>)</span><br><span class="line">  <span class="attr">description</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>(<span class="string">'decimal'</span>)</span><br><span class="line">  <span class="attr">price</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">stock</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@CreateDateColumn</span>()</span><br><span class="line">  <span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@UpdateDateColumn</span>()</span><br><span class="line">  <span class="attr">updated_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p>代码实现的特点：</p>
<ul>
<li>使用 <code>text</code> 类型存储描述，支持长文本内容</li>
<li>使用 <code>decimal</code> 类型存储价格，避免浮点数计算误差</li>
<li><code>stock</code> 字段直接使用普通的数值类型，便于进行库存相关的计算</li>
</ul>
<p>商品表的字段及其业务含义如下：</p>
<ul>
<li><code>id</code>：主键，用于唯一标识每个商品，类型为 <code>UUID</code></li>
<li><code>name</code>：商品名称，帮助用户识别商品</li>
<li><code>description</code>：商品描述，用于展示商品的详细信息</li>
<li><code>price</code>：商品价格，定义用户在购买该商品时的成本</li>
<li><code>stock</code>：商品库存数量，代表当前商品的剩余数量</li>
<li><code>created_at</code> 和 <code>updated_at</code>：创建时间和更新时间，记录商品上架和更新的时间</li>
</ul>
<h4 id="122-关联关系分析"><a class="markdownIt-Anchor" href="#122-关联关系分析"></a> 1.2.2. 关联关系分析</h4>
<p><code>Products</code> 实体与其他实体建立了多个关联关系：</p>
<figure class="highlight ts"><table><tbody><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_">Categories</span> } <span class="keyword">from</span> <span class="string">'./categories.entity'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">OrderItems</span> } <span class="keyword">from</span> <span class="string">'./order-items.entity'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">CartItems</span> } <span class="keyword">from</span> <span class="string">'./cart-items.entity'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">InventoryLogs</span> } <span class="keyword">from</span> <span class="string">'./inventory-logs.entity'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Products</span> {</span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line"></span><br><span class="line">  <span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Categories</span>, <span class="function"><span class="params">category</span> =&gt;</span> category.<span class="property">products</span>)</span><br><span class="line">  <span class="attr">category</span>: <span class="title class_">Categories</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">OrderItems</span>, <span class="function"><span class="params">orderItem</span> =&gt;</span> orderItem.<span class="property">product</span>)</span><br><span class="line">  <span class="attr">orderItems</span>: <span class="title class_">OrderItems</span>[];</span><br><span class="line"></span><br><span class="line">  <span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">CartItems</span>, <span class="function"><span class="params">cartItem</span> =&gt;</span> cartItem.<span class="property">product</span>)</span><br><span class="line">  <span class="attr">cartItems</span>: <span class="title class_">CartItems</span>[];</span><br><span class="line"></span><br><span class="line">  <span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">InventoryLogs</span>, <span class="function"><span class="params">inventoryLog</span> =&gt;</span> inventoryLog.<span class="property">product</span>)</span><br><span class="line">  <span class="attr">inventoryLogs</span>: <span class="title class_">InventoryLogs</span>[];</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<ol>
<li>商品 - 类别关系（<code>@ManyToOne</code>)
<ul>
<li>一个商品属于一个类别</li>
<li>支持商品分类管理和分类检索</li>
<li>多对一的关系使得类别可以包含多个商品</li>
</ul>
</li>
<li>商品 - 订单项关系（<code>@OneToMany</code>)
<ul>
<li>一个商品可以出现在多个订单中</li>
<li>通过 <code>OrderItems</code> 中间表存储具体的购买数量和价格</li>
<li>支持订单历史查询和销售统计</li>
</ul>
</li>
<li>商品 - 购物车项关系（<code>@OneToMany</code>)
<ul>
<li>一个商品可以被加入多个用户的购物车</li>
<li>通过 <code>CartItems</code> 中间表记录购物车中的商品数量</li>
</ul>
</li>
<li>商品 - 库存日志关系（<code>@OneToMany</code>)
<ul>
<li>记录商品库存变动历史</li>
<li>支持库存追踪和审计</li>
</ul>
</li>
</ol>
<h2 id="13-类别"><a class="markdownIt-Anchor" href="#13-类别"></a> 1.3. 类别</h2>
<p>类别实体是商品分类的基础，它帮助我们组织和管理商品，提供更好的浏览和检索体验。一个良好的类别系统能够帮助用户更快地找到所需商品，同时也便于商家进行商品管理。</p>
<blockquote>
<p>当平台增加新类别「智能家居」时，它会被添加到 <code>Categories</code> 表中。用户在浏览智能家居产品时，只需点击此类别，即可看到所有相关商品。</p>
</blockquote>
<h4 id="131-代码实现分析"><a class="markdownIt-Anchor" href="#131-代码实现分析"></a> 1.3.1. 代码实现分析</h4>
<figure class="highlight ts"><table><tbody><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_">Entity</span>, <span class="title class_">PrimaryGeneratedColumn</span>, <span class="title class_">Column</span>, <span class="title class_">CreateDateColumn</span>, <span class="title class_">UpdateDateColumn</span>, <span class="title class_">OneToMany</span> } <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Categories</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">name</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>(<span class="string">'text'</span>)</span><br><span class="line">  <span class="attr">description</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@CreateDateColumn</span>()</span><br><span class="line">  <span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@UpdateDateColumn</span>()</span><br><span class="line">  <span class="attr">updated_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p>类别表的字段及其业务含义如下：</p>
<ul>
<li><code>id</code>：主键，唯一标识类别，类型为 <code>UUID</code></li>
<li><code>name</code>：类别名称，例如「电子产品」或「家具」</li>
<li><code>description</code>：类别描述，进一步解释类别内容</li>
<li><code>created_at</code> 和 <code>updated_at</code>：创建和更新时间，记录类别的管理信息</li>
</ul>
<h4 id="132-关联关系分析"><a class="markdownIt-Anchor" href="#132-关联关系分析"></a> 1.3.2. 关联关系分析</h4>
<p><code>Categories</code> 实体主要与 <code>Products</code> 实体建立了一对多的关联关系：</p>
<figure class="highlight ts"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">Products</span> } <span class="keyword">from</span> <span class="string">'./products.entity'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Categories</span> {</span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line"></span><br><span class="line">  <span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">Products</span>, <span class="function"><span class="params">product</span> =&gt;</span> product.<span class="property">category</span>)</span><br><span class="line">  <span class="attr">products</span>: <span class="title class_">Products</span>[];</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<ol>
<li>类别 - 商品关系（<code>@OneToMany</code>)
<ul>
<li>一个类别可以包含多个商品</li>
<li>体现了分类组织的层次结构</li>
<li>支持按类别查询和统计商品</li>
</ul>
</li>
</ol>
<h2 id="14-订单"><a class="markdownIt-Anchor" href="#14-订单"></a> 1.4. 订单</h2>
<p>订单是电商系统中最核心的业务实体之一，它记录了交易的全过程，连接了用户、商品、支付等多个业务环节。一个完善的订单系统需要处理订单状态流转、支付流程、商品库存等复杂的业务场景。</p>
<blockquote>
<p>当用户下单购买一部智能手表，总价为 200 元，订单状态为「待支付」。在用户支付成功后，订单状态更新为「已支付」。</p>
</blockquote>
<h4 id="141-代码实现分析"><a class="markdownIt-Anchor" href="#141-代码实现分析"></a> 1.4.1. 代码实现分析</h4>
<figure class="highlight ts"><table><tbody><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><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> {</span><br><span class="line">  <span class="title class_">Entity</span>,</span><br><span class="line">  <span class="title class_">PrimaryGeneratedColumn</span>,</span><br><span class="line">  <span class="title class_">Column</span>,</span><br><span class="line">  <span class="title class_">CreateDateColumn</span>,</span><br><span class="line">  <span class="title class_">UpdateDateColumn</span>,</span><br><span class="line">  <span class="title class_">ManyToOne</span>,</span><br><span class="line">  <span class="title class_">OneToMany</span></span><br><span class="line">} <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Orders</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>(<span class="string">'decimal'</span>)</span><br><span class="line">  <span class="attr">total_price</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">status</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@CreateDateColumn</span>()</span><br><span class="line">  <span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@UpdateDateColumn</span>()</span><br><span class="line">  <span class="attr">updated_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li><code>id</code>：订单的唯一标识符，使用 <code>UUID</code> 类型</li>
<li><code>total_price</code>：订单总价，使用 <code>decimal</code> 类型确保精确计算</li>
<li><code>status</code>：订单状态，用于追踪订单的处理流程</li>
<li><code>created_at</code> 和 <code>updated_at</code>：记录订单的创建和更新时间</li>
</ul>
<h4 id="142-关联关系分析"><a class="markdownIt-Anchor" href="#142-关联关系分析"></a> 1.4.2. 关联关系分析</h4>
<p><code>Orders</code> 实体与其他实体建立了多个关联关系：</p>
<figure class="highlight ts"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">Users</span> } <span class="keyword">from</span> <span class="string">'./users.entity'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">OrderItems</span> } <span class="keyword">from</span> <span class="string">'./order-items.entity'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Orders</span> {</span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line"></span><br><span class="line">  <span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Users</span>, <span class="function"><span class="params">user</span> =&gt;</span> user.<span class="property">orders</span>)</span><br><span class="line">  <span class="attr">user</span>: <span class="title class_">Users</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">OrderItems</span>, <span class="function"><span class="params">orderItem</span> =&gt;</span> orderItem.<span class="property">order</span>)</span><br><span class="line">  <span class="attr">orderItems</span>: <span class="title class_">OrderItems</span>[];</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p>这些关联关系支持了完整的订单业务流程：</p>
<ol>
<li>订单 - 用户关系（<code>@ManyToOne</code>)
<ul>
<li>每个订单必须属于一个用户</li>
<li>支持用户订单历史查询</li>
<li>便于进行用户消费分析</li>
</ul>
</li>
<li>订单 - 订单项关系（<code>@OneToMany</code>)
<ul>
<li>一个订单可以包含多个商品</li>
<li>通过 <code>OrderItems</code> 存储具体的商品信息和数量</li>
<li>支持订单明细查询和统计</li>
</ul>
</li>
</ol>
<h2 id="15-订单项"><a class="markdownIt-Anchor" href="#15-订单项"></a> 1.5. 订单项</h2>
<p>订单项实体记录了订单中每个商品的具体购买信息，包括数量、单价和总价等。它不仅连接了订单和商品，还保存了购买时的价格快照，这对于订单历史记录和财务核算都很重要。</p>
<h4 id="151-代码实现分析"><a class="markdownIt-Anchor" href="#151-代码实现分析"></a> 1.5.1. 代码实现分析</h4>
<figure class="highlight ts"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">Entity</span>, <span class="title class_">PrimaryGeneratedColumn</span>, <span class="title class_">Column</span>, <span class="title class_">ManyToOne</span> } <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">OrderItems</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">quantity</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>(<span class="string">'decimal'</span>)</span><br><span class="line">  <span class="attr">price</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>(<span class="string">'decimal'</span>)</span><br><span class="line">  <span class="attr">total_price</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li><code>id</code>：订单项的唯一标识符，使用 <code>UUID</code> 类型</li>
<li><code>quantity</code>：购买数量</li>
<li><code>price</code>：商品单价的快照，使用 <code>decimal</code> 类型</li>
<li><code>total_price</code>：该项商品的总价，使用 <code>decimal</code> 类型</li>
</ul>
<h4 id="152-关联关系分析"><a class="markdownIt-Anchor" href="#152-关联关系分析"></a> 1.5.2. 关联关系分析</h4>
<p><code>OrderItems</code> 实体与其他实体建立了多个多对一的关联关系：</p>
<ol>
<li>
<p>订单项 - 订单关系（<code>@ManyToOne</code>)</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Orders</span>, <span class="function"><span class="params">order</span> =&gt;</span> order.<span class="property">orderItems</span>)</span><br><span class="line"><span class="attr">order</span>: <span class="title class_">Orders</span>;</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li>多个订单项属于同一个订单</li>
<li>通过这个关系可以获取订单的完整商品清单</li>
<li>支持订单总价计算和商品统计</li>
</ul>
</li>
<li>
<p>订单项 - 商品关系（<code>@ManyToOne</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Products</span>, <span class="function"><span class="params">product</span> =&gt;</span> product.<span class="property">orderItems</span>)</span><br><span class="line"><span class="attr">product</span>: <span class="title class_">Products</span>;</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li>记录该订单项对应的具体商品</li>
<li>支持商品销售统计和分析</li>
<li>可以追踪商品的购买历史</li>
</ul>
</li>
</ol>
<h2 id="16-购物车"><a class="markdownIt-Anchor" href="#16-购物车"></a> 1.6. 购物车</h2>
<p>每个用户都有一个购物车，用于暂存待购买的商品信息。</p>
<p>购物车实体记录了用户在线上选择和加入的商品，是下单前的临时存储。它与订单实体有着类似的结构，但服务于不同的业务场景。</p>
<h4 id="161-代码实现分析"><a class="markdownIt-Anchor" href="#161-代码实现分析"></a> 1.6.1. 代码实现分析</h4>
<figure class="highlight ts"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">Entity</span>, <span class="title class_">PrimaryGeneratedColumn</span>, <span class="title class_">CreateDateColumn</span>, <span class="title class_">UpdateDateColumn</span>, <span class="title class_">OneToOne</span>, <span class="title class_">OneToMany</span> } <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">Users</span> } <span class="keyword">from</span> <span class="string">'./users.entity'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">CartItems</span> } <span class="keyword">from</span> <span class="string">'./cart-items.entity'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Carts</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@CreateDateColumn</span>()</span><br><span class="line">  <span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@UpdateDateColumn</span>()</span><br><span class="line">  <span class="attr">updated_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p>代码实现的特点：</p>
<ul>
<li>使用一对一关系与用户实体关联，确保每个用户只有一个购物车</li>
<li>包含基本的时间戳字段，跟踪购物车的创建和更新</li>
</ul>
<p>购物车表的字段及其业务含义如下：</p>
<ul>
<li><code>id</code>：购物车的唯一标识符，使用 <code>UUID</code> 类型</li>
<li><code>created_at</code> 和 <code>updated_at</code>：记录购物车的创建和更新时间</li>
</ul>
<h4 id="162-关联关系分析"><a class="markdownIt-Anchor" href="#162-关联关系分析"></a> 1.6.2. 关联关系分析</h4>
<p><code>Carts</code> 实体与其他实体建立了以下关联关系：</p>
<ol>
<li>
<p>购物车 - 用户关系（<code>@OneToOne</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@OneToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Users</span>, <span class="function"><span class="params">user</span> =&gt;</span> user.<span class="property">cart</span>)</span><br><span class="line"><span class="attr">user</span>: <span class="title class_">Users</span>;</span><br></pre></td></tr></tbody></table></figure>
</li>
<li>
<p>购物车 - 购物车项关系（<code>@OneToMany</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@OneToMany</span>(<span class="function">() =&gt;</span> <span class="title class_">CartItems</span>, <span class="function"><span class="params">cartItem</span> =&gt;</span> cartItem.<span class="property">cart</span>)</span><br><span class="line"><span class="attr">cartItems</span>: <span class="title class_">CartItems</span>[];</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li>一个购物车可以包含多个购物车项</li>
<li>通过这个关系可以获取购物车中的商品列表</li>
</ul>
</li>
</ol>
<h2 id="17-购物车项"><a class="markdownIt-Anchor" href="#17-购物车项"></a> 1.7. 购物车项</h2>
<p>购物车项实体记录了用户在购物车中选择的商品及其数量，它与订单项实体有着类似的结构。</p>
<blockquote>
<p>用户在购物车中添加了两部智能手表，购物车项记录该商品 ID、数量为 2，以及关联的购物车 ID。</p>
</blockquote>
<h4 id="171-代码实现分析"><a class="markdownIt-Anchor" href="#171-代码实现分析"></a> 1.7.1. 代码实现分析</h4>
<figure class="highlight ts"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">Entity</span>, <span class="title class_">PrimaryGeneratedColumn</span>, <span class="title class_">Column</span>, <span class="title class_">ManyToOne</span> } <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">CartItems</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">quantity</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p><code>CartItems</code> 实体的特点：</p>
<ul>
<li>使用多对一关系连接购物车和商品实体</li>
<li>记录了商品的购买数量，用于计算购物车总价</li>
</ul>
<h4 id="172-关联关系分析"><a class="markdownIt-Anchor" href="#172-关联关系分析"></a> 1.7.2. 关联关系分析</h4>
<ol>
<li>
<p>购物车项 - 购物车关系（<code>@ManyToOne</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Carts</span>, <span class="function"><span class="params">cart</span> =&gt;</span> cart.<span class="property">cartItems</span>)</span><br><span class="line"><span class="attr">cart</span>: <span class="title class_">Carts</span>;</span><br></pre></td></tr></tbody></table></figure>
</li>
<li>
<p>购物车项 - 商品关系（<code>@ManyToOne</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Products</span>, <span class="function"><span class="params">product</span> =&gt;</span> product.<span class="property">cartItems</span>)</span><br><span class="line"><span class="attr">product</span>: <span class="title class_">Products</span>;</span><br></pre></td></tr></tbody></table></figure>
</li>
</ol>
<h2 id="18-支付"><a class="markdownIt-Anchor" href="#18-支付"></a> 1.8. 支付</h2>
<p>支付实体记录了用户在完成下单后的支付信息，包括支付金额、支付状态等。它与订单实体有着直接的关联关系。</p>
<h4 id="181-代码实现分析"><a class="markdownIt-Anchor" href="#181-代码实现分析"></a> 1.8.1. 代码实现分析</h4>
<figure class="highlight ts"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">Entity</span>, <span class="title class_">PrimaryGeneratedColumn</span>, <span class="title class_">Column</span>, <span class="title class_">CreateDateColumn</span>, <span class="title class_">ManyToOne</span> } <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Payments</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>(<span class="string">'decimal'</span>)</span><br><span class="line">  <span class="attr">amount</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">status</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@CreateDateColumn</span>()</span><br><span class="line">  <span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p><code>Payments</code> 实体的特点：</p>
<ul>
<li>使用多对一关系连接订单和用户实体</li>
<li>记录了支付的金额和状态</li>
<li>包含支付的创建时间戳</li>
</ul>
<h4 id="182-关联关系分析"><a class="markdownIt-Anchor" href="#182-关联关系分析"></a> 1.8.2. 关联关系分析</h4>
<ol>
<li>
<p>支付 - 订单关系（<code>@ManyToOne</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Orders</span>, <span class="function"><span class="params">order</span> =&gt;</span> order.<span class="property">id</span>)</span><br><span class="line"><span class="attr">order</span>: <span class="title class_">Orders</span>;</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li>一笔订单可以有多个支付记录</li>
<li>通过这个关系可以获取支付所属的订单信息</li>
</ul>
</li>
<li>
<p>支付 - 用户关系（<code>@ManyToOne</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Users</span>, <span class="function"><span class="params">user</span> =&gt;</span> user.<span class="property">payments</span>)</span><br><span class="line"><span class="attr">user</span>: <span class="title class_">Users</span>;</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li>一个用户可以有多笔支付记录</li>
<li>通过这个关系可以获取支付所属的用户信息</li>
</ul>
</li>
</ol>
<h2 id="19-地址"><a class="markdownIt-Anchor" href="#19-地址"></a> 1.9. 地址</h2>
<p>地址实体记录了用户的收货地址信息，包括街道、城市、州 / 省、邮编和国家等详细信息。这些信息在用户下单时需要用到，也可以用于生成发货标签等。</p>
<h4 id="191-代码实现分析"><a class="markdownIt-Anchor" href="#191-代码实现分析"></a> 1.9.1. 代码实现分析</h4>
<figure class="highlight ts"><table><tbody><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><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">Entity</span>, <span class="title class_">PrimaryGeneratedColumn</span>, <span class="title class_">Column</span>, <span class="title class_">CreateDateColumn</span>, <span class="title class_">UpdateDateColumn</span>, <span class="title class_">ManyToOne</span> } <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">Addresses</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">street</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">city</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">state</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">postal_code</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">country</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@CreateDateColumn</span>()</span><br><span class="line">  <span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@UpdateDateColumn</span>()</span><br><span class="line">  <span class="attr">updated_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<h4 id="192-关联关系分析"><a class="markdownIt-Anchor" href="#192-关联关系分析"></a> 1.9.2. 关联关系分析</h4>
<ol>
<li>
<p>地址 - 用户关系（<code>@ManyToOne</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Users</span>, <span class="function"><span class="params">user</span> =&gt;</span> user.<span class="property">addresses</span>)</span><br><span class="line"><span class="attr">user</span>: <span class="title class_">Users</span>; </span><br></pre></td></tr></tbody></table></figure>
<ul>
<li>一个用户可以有多个地址信息</li>
<li>通过这个关系可以获取地址所属的用户信息</li>
</ul>
</li>
</ol>
<h2 id="110-库存日志"><a class="markdownIt-Anchor" href="#110-库存日志"></a> 1.10. 库存日志</h2>
<p>库存日志实体记录了商品库存的变动历史，包括每次库存增减的数量和时间。这些记录对于库存管理、库存盘点和异常排查都非常重要。</p>
<h4 id="1101-代码实现分析"><a class="markdownIt-Anchor" href="#1101-代码实现分析"></a> 1.10.1. 代码实现分析</h4>
<figure class="highlight ts"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">Entity</span>, <span class="title class_">PrimaryGeneratedColumn</span>, <span class="title class_">Column</span>, <span class="title class_">CreateDateColumn</span>, <span class="title class_">ManyToOne</span> } <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Entity</span>()</span><br><span class="line"><span class="keyword">export</span> <span class="keyword">class</span> <span class="title class_">InventoryLogs</span> {</span><br><span class="line">  <span class="meta">@PrimaryGeneratedColumn</span>(<span class="string">'uuid'</span>)</span><br><span class="line">  <span class="attr">id</span>: <span class="built_in">string</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@Column</span>()</span><br><span class="line">  <span class="attr">change</span>: <span class="built_in">number</span>;</span><br><span class="line"></span><br><span class="line">  <span class="meta">@CreateDateColumn</span>()</span><br><span class="line">  <span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br><span class="line"></span><br><span class="line">  <span class="comment">// ...</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>
<p><code>InventoryLogs</code> 实体的特点：</p>
<ul>
<li>使用多对一关系与商品实体关联</li>
<li>记录了库存变动数量（<code>change</code>)，正数表示入库，负数表示出库</li>
<li>包含时间戳，记录每次库存变动的具体时间点</li>
</ul>
<h4 id="1102-关联关系分析"><a class="markdownIt-Anchor" href="#1102-关联关系分析"></a> 1.10.2. 关联关系分析</h4>
<ol>
<li>
<p>库存日志 - 商品关系（<code>@ManyToOne</code>）</p>
 <figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@ManyToOne</span>(<span class="function">() =&gt;</span> <span class="title class_">Products</span>, <span class="function"><span class="params">product</span> =&gt;</span> product.<span class="property">inventoryLogs</span>)</span><br><span class="line"><span class="attr">product</span>: <span class="title class_">Products</span>;</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li>一个商品可以有多条库存变动记录</li>
<li>通过这个关系可以追踪特定商品的库存变动历史</li>
</ul>
</li>
</ol>
<h1 id="2-创建数据库迁移文件"><a class="markdownIt-Anchor" href="#2-创建数据库迁移文件"></a> 2. 创建数据库迁移文件</h1>
<p>在开发应用程序时，数据库模式的更新是一项常见而重要的工作，尤其是在应用不断演进的过程中。</p>
<p>假设我们在开发一个应用，并需要更新数据库的表结构，比如添加新字段、修改字段类型等。如何在不丢失现有数据的情况下进行这些修改呢？</p>
<p>TypeORM 可以帮助我们轻松处理数据库操作。它内置了强大的迁移功能，使我们能够定义数据库结构变更并自动应用到数据库中。</p>
<h2 id="21-添加自定义命令"><a class="markdownIt-Anchor" href="#21-添加自定义命令"></a> 2.1. 添加自定义命令</h2>
<p>首先，我们在 <code>package.json</code> 中添加一些脚本来管理 TypeORM 的迁移操作。这些脚本将自动构建项目并运行相应的迁移命令，方便我们快速执行迁移操作：</p>
<figure class="highlight json"><table><tbody><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></pre></td><td class="code"><pre><span class="line"><span class="punctuation">{</span></span><br><span class="line">  <span class="attr">"scripts"</span><span class="punctuation">:</span> <span class="punctuation">{</span></span><br><span class="line">    <span class="comment">// ...</span></span><br><span class="line">    <span class="attr">"typeorm"</span><span class="punctuation">:</span> <span class="string">"typeorm-ts-node-commonjs -d src/config/data-source.ts"</span><span class="punctuation">,</span></span><br><span class="line">    <span class="attr">"migration:initialize"</span><span class="punctuation">:</span> <span class="string">"yarn build &amp;&amp; yarn typeorm migration:generate src/migrations/InitialMigration"</span><span class="punctuation">,</span></span><br><span class="line">    <span class="attr">"migration:generate"</span><span class="punctuation">:</span> <span class="string">"yarn build &amp;&amp; yarn typeorm migration:generate"</span><span class="punctuation">,</span></span><br><span class="line">    <span class="attr">"migration:run"</span><span class="punctuation">:</span> <span class="string">"yarn build &amp;&amp; yarn typeorm migration:run"</span><span class="punctuation">,</span></span><br><span class="line">    <span class="attr">"migration:revert"</span><span class="punctuation">:</span> <span class="string">"yarn build &amp;&amp; yarn typeorm migration:revert"</span></span><br><span class="line">  <span class="punctuation">}</span></span><br><span class="line"><span class="punctuation">}</span></span><br></pre></td></tr></tbody></table></figure>
<p>让我们一行一行地分析这些脚本的作用：</p>
<ul>
<li><code>typeorm</code>：指定 TypeORM 的配置文件路径（<code>src/config/data-source.ts</code>），它是所有 TypeORM 操作的基础</li>
<li><code>migration:initialize</code>：生成 <code>InitialMigration</code> 迁移文件</li>
<li><code>migration:generate</code>：生成新的迁移文件
<ul>
<li>用法：<code>yarn migration:generate src/migrations/xxx</code></li>
</ul>
</li>
<li><code>migration:run</code>：执行所有还未运行的迁移，应用到数据库中</li>
<li><code>migration:revert</code>：撤销上一次迁移，通常用于回滚数据库结构到上一个状态</li>
</ul>
<h2 id="22-配置-typeorm-数据源"><a class="markdownIt-Anchor" href="#22-配置-typeorm-数据源"></a> 2.2. 配置 TypeORM 数据源</h2>
<p>接下来，我们需要设置 TypeORM 的数据库配置。</p>
<p>在项目的 <code>src/config/data-source.ts</code> 文件中，我们使用 <code>DataSourceOptions</code> 来定义数据库连接的详细信息。</p>
<p>这里我们还使用了 <code>@nestjs/config</code> 模块来动态读取环境变量，这样在不同环境中可以使用不同的数据库配置。</p>
<figure class="highlight ts"><table><tbody><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><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> { <span class="title class_">ConfigService</span> } <span class="keyword">from</span> <span class="string">'@nestjs/config'</span>;</span><br><span class="line"><span class="keyword">import</span> { <span class="title class_">DataSource</span>, <span class="title class_">DataSourceOptions</span> } <span class="keyword">from</span> <span class="string">'typeorm'</span>;</span><br><span class="line"><span class="keyword">import</span> { config } <span class="keyword">from</span> <span class="string">'dotenv'</span>;</span><br><span class="line"></span><br><span class="line"><span class="title function_">config</span>();</span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> configService = <span class="keyword">new</span> <span class="title class_">ConfigService</span>();</span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> <span class="attr">dataSourceOptions</span>: <span class="title class_">DataSourceOptions</span> = {</span><br><span class="line">  <span class="attr">type</span>: configService.<span class="property">get</span>&lt;<span class="built_in">any</span>&gt;(<span class="string">'DB_TYPE'</span>, <span class="string">'mysql'</span>),</span><br><span class="line">  <span class="attr">host</span>: configService.<span class="property">get</span>&lt;<span class="built_in">string</span>&gt;(<span class="string">'DB_HOST'</span>),</span><br><span class="line">  <span class="attr">port</span>: configService.<span class="property">get</span>&lt;<span class="built_in">number</span>&gt;(<span class="string">'DB_PORT'</span>),</span><br><span class="line">  <span class="attr">username</span>: configService.<span class="property">get</span>&lt;<span class="built_in">string</span>&gt;(<span class="string">'DB_USER'</span>),</span><br><span class="line">  <span class="attr">password</span>: configService.<span class="property">get</span>&lt;<span class="built_in">string</span>&gt;(<span class="string">'DB_PASSWORD'</span>),</span><br><span class="line">  <span class="attr">database</span>: configService.<span class="property">get</span>&lt;<span class="built_in">string</span>&gt;(<span class="string">'DB_NAME'</span>),</span><br><span class="line">  <span class="attr">synchronize</span>: configService.<span class="property">get</span>&lt;<span class="built_in">string</span>&gt;(<span class="string">'APP_ENV'</span>) === <span class="string">'development'</span>,</span><br><span class="line">  <span class="attr">entities</span>: [<span class="string">'dist/entities/*.entity{.ts,.js}'</span>],</span><br><span class="line">  <span class="attr">migrations</span>: [<span class="string">'dist/migrations/*{.ts,.js}'</span>],</span><br><span class="line">  <span class="attr">subscribers</span>: []</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="keyword">export</span> <span class="keyword">default</span> <span class="keyword">new</span> <span class="title class_">DataSource</span>(dataSourceOptions);</span><br></pre></td></tr></tbody></table></figure>
<ul>
<li><code>type</code>：指定数据库类型，这里我们通过环境变量 <code>DB_TYPE</code> 来设置，默认为 MySQL</li>
<li><code>host</code>、<code>port</code>、<code>username</code>、<code>password</code>、<code>database</code>：这些参数是数据库连接的必要信息，都可以通过环境变量配置</li>
<li><code>synchronize</code>：如果 <code>APP_ENV</code> 为 <code>development</code>，则会启用同步模式，让 TypeORM 自动更新数据库表结构
<ul>
<li>注意：生产环境下建议禁用此项</li>
</ul>
</li>
<li><code>entities</code> 和 <code>migrations</code>：指定实体和迁移文件的路径。TypeORM 会使用这些路径找到相关文件</li>
</ul>
<h2 id="23-生成数据库迁移文件"><a class="markdownIt-Anchor" href="#23-生成数据库迁移文件"></a> 2.3. 生成数据库迁移文件</h2>
<p>当配置完成后，我们可以通过以下命令来生成用于初始化数据库的迁移文件：</p>
<figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">yarn migration:initialize</span><br></pre></td></tr></tbody></table></figure>
<p>这条命令会自动构建项目，并使用 TypeORM 生成一个迁移文件（位于 <code>src/migrations</code>，且默认命名为 <code>数字数字数字-InitialMigration.ts</code>）。</p>
<p>这个文件会包含创建、修改或删除表结构的 SQL 语句。例如，如果你添加了一个新的字段，生成的迁移文件就会包含一个 <code>ALTER TABLE</code> 语句。</p>
<h2 id="24-执行迁移"><a class="markdownIt-Anchor" href="#24-执行迁移"></a> 2.4. 执行迁移</h2>
<p>生成迁移文件后，使用以下命令将其应用到数据库：</p>
<figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">yarn migration:run</span><br></pre></td></tr></tbody></table></figure>
<p>此命令会检查并执行所有尚未在数据库中应用的迁移。这样可以确保你的数据库结构与最新的迁移文件一致。</p>
<h2 id="25-回滚迁移"><a class="markdownIt-Anchor" href="#25-回滚迁移"></a> 2.5. 回滚迁移</h2>
<p>在开发过程中，偶尔可能需要回滚上次迁移，例如在测试或调试时。使用以下命令可以撤销上一次迁移：</p>
<figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">yarn migration:revert</span><br></pre></td></tr></tbody></table></figure>
<p>TypeORM 会自动识别上次执行的迁移，并撤销相应的更改，恢复到之前的数据库结构。</p>
<h1 id="3-设置数据库索引"><a class="markdownIt-Anchor" href="#3-设置数据库索引"></a> 3. 设置数据库索引</h1>
<p>在开发应用程序时，尤其是当数据库中的数据量越来越大时，查询性能变得至关重要。</p>
<p>数据库索引是一种数据结构，它帮助数据库管理系统（DBMS）高效地检索数据。索引就像书籍中的目录，它可以快速定位到某个数据的位置，而不是扫描整个表。当我们对数据库表进行查询时，索引可以显著提高查询性能，尤其是在处理大量数据时。</p>
<p>在 MySQL 中，索引通常应用于那些需要频繁查询的字段。常见的索引类型有：</p>
<ul>
<li>主键索引：自动为表的主键字段创建</li>
<li>唯一索引：确保每个值唯一</li>
<li>普通索引：加速数据检索，但不强制唯一性</li>
<li>全文索引：用于加速文本内容的检索</li>
</ul>
<p>没有索引的情况下，数据库在执行查询时必须扫描整个表，逐行比较数据。这种方式在小型表中可能没什么问题，但在数据量较大时，会导致性能急剧下降。</p>
<blockquote>
<p>假设我们的购物平台，数据库中存储了数百万条订单记录。当用户搜索特定订单时，如果没有适当的索引，系统可能会扫描整个订单表来找到匹配的记录。随着数据量增加，查询速度变得非常慢，甚至可能导致系统响应延迟。</p>
<p>使用索引后，数据库不再需要扫描整个表，而是通过索引快速定位到目标数据，从而显著提升查询速度。</p>
</blockquote>
<p>在 NestJS 中，我们可以通过 TypeORM 为实体字段添加索引。TypeORM 提供了 <code>@Index()</code> 装饰器，允许我们在数据库表的字段上添加索引。</p>
<h2 id="31-用户"><a class="markdownIt-Anchor" href="#31-用户"></a> 3.1. 用户</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@CreateDateColumn</span>()</span><br><span class="line"><span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br></pre></td></tr></tbody></table></figure>
<p>在 <code>Users</code> 实体中，我们使用了 <code>@Index()</code> 装饰器来为 <code>created_at</code> 字段添加索引。</p>
<p>在大多数应用程序中，<code>created_at</code> 字段通常用于按照时间排序或进行时间范围查询。</p>
<blockquote>
<p>例如，用户可能需要查看某一时间段内的所有注册用户，或者获取最近创建的用户列表。</p>
</blockquote>
<p>假设在应用程序中，用户经常执行以下查询：</p>
<ul>
<li>查询某个时间段内注册的用户。</li>
<li>按照注册时间排序显示用户列表。</li>
</ul>
<p>如果没有为 <code>created_at</code> 字段添加索引，数据库会需要扫描整个用户表来执行这些查询，这样会导致性能问题。添加索引后，数据库可以通过索引快速查找和排序数据，显著提高查询速度，尤其是在数据量较大的情况下。</p>
<h4 id="311-关系字段为何不需要索引"><a class="markdownIt-Anchor" href="#311-关系字段为何不需要索引"></a> 3.1.1. 关系字段为何不需要索引？</h4>
<p>这时候就有人问了：「难道像 <code>orders</code>、<code>cart</code> 这些字段，用户就不会查询了吗？如果经常用到，为什么不为它们加个索引呢？」答案是：确实不需要。</p>
<p>在 TypeORM 中，关系字段（比如 <code>orders</code> 和 <code>cart</code>）通常是外键字段，数据库会自动为这些字段创建索引。例如，在 <code>Users</code> 实体中，<code>orders</code> 字段是通过 <code>@OneToMany</code> 与 <code>Orders</code> 实体关联的。虽然我们没有显式地为 <code>orders</code> 字段添加索引，但在 <code>Orders</code> 表中，<code>user</code> 字段作为外键会自动被索引。</p>
<p>这意味着，当我们查询某个用户的所有订单时，数据库会直接利用 <code>Orders</code> 表中自动创建的 <code>user</code> 索引，来加速查询。而我们不需要额外为 <code>orders</code> 字段添加索引，TypeORM 和数据库已经为我们处理好了这部分的优化。</p>
<h2 id="32-商品"><a class="markdownIt-Anchor" href="#32-商品"></a> 3.2. 商品</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@Column</span>(<span class="string">'decimal'</span>)</span><br><span class="line"><span class="attr">price</span>: <span class="built_in">number</span>;</span><br></pre></td></tr></tbody></table></figure>
<p><code>price</code> 字段通常会用于以下几种查询：</p>
<ul>
<li>按照价格范围查询产品，例如查找价格低于某个值的所有产品</li>
<li>按照价格排序，例如将产品列表按价格从低到高或从高到低排序</li>
</ul>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@Column</span>()</span><br><span class="line"><span class="attr">stock</span>: <span class="built_in">number</span>;</span><br></pre></td></tr></tbody></table></figure>
<p><code>stock</code> 字段通常用于以下查询场景：</p>
<ul>
<li>查找库存数量为零或低于某个值的产品（例如「缺货」产品或「库存预警」产品）</li>
<li>按照库存数量排序，帮助商家快速查看库存最少的产品</li>
</ul>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@CreateDateColumn</span>()</span><br><span class="line"><span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br></pre></td></tr></tbody></table></figure>
<p>所有的 <code>created_at</code> 字段都需要添加索引。</p>
<h2 id="33-支付"><a class="markdownIt-Anchor" href="#33-支付"></a> 3.3. 支付</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@CreateDateColumn</span>()</span><br><span class="line"><span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br></pre></td></tr></tbody></table></figure>
<h2 id="34-订单"><a class="markdownIt-Anchor" href="#34-订单"></a> 3.4. 订单</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@Column</span>()</span><br><span class="line"><span class="attr">status</span>: <span class="built_in">string</span>;</span><br></pre></td></tr></tbody></table></figure>
<p><code>status</code> 字段通常用于查询订单的状态，例如：</p>
<ul>
<li>查询某一状态的订单（如「待处理」、「已发货」、「已完成」等）</li>
<li>按照订单状态统计订单数量</li>
</ul>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@CreateDateColumn</span>()</span><br><span class="line"><span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br></pre></td></tr></tbody></table></figure>
<h2 id="35-订单项"><a class="markdownIt-Anchor" href="#35-订单项"></a> 3.5. 订单项</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@Column</span>()</span><br><span class="line"><span class="attr">quantity</span>: <span class="built_in">number</span>;</span><br></pre></td></tr></tbody></table></figure>
<p><code>quantity</code> 字段通常在以下情况中用于查询：</p>
<ul>
<li>查询具有特定数量的订单项（例如查询某种商品的批量购买情况）</li>
<li>按照数量对订单项进行筛选或排序</li>
</ul>
<h2 id="36-类别"><a class="markdownIt-Anchor" href="#36-类别"></a> 3.6. 类别</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@Column</span>()</span><br><span class="line"><span class="attr">name</span>: <span class="built_in">string</span>;</span><br></pre></td></tr></tbody></table></figure>
<p><code>name</code> 字段是分类的唯一标识，用于以下情况：</p>
<ul>
<li>按类别名称搜索产品类别（例如，用户希望快速找到特定名称的类别）</li>
<li>在名称字段上进行排序或进行自动完成的匹配查询</li>
</ul>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@CreateDateColumn</span>()</span><br><span class="line"><span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br></pre></td></tr></tbody></table></figure>
<h2 id="37-购物车"><a class="markdownIt-Anchor" href="#37-购物车"></a> 3.7. 购物车</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@CreateDateColumn</span>()</span><br><span class="line"><span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br></pre></td></tr></tbody></table></figure>
<h2 id="38-地址"><a class="markdownIt-Anchor" href="#38-地址"></a> 3.8. 地址</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@Column</span>()</span><br><span class="line"><span class="attr">postal_code</span>: <span class="built_in">string</span>;</span><br></pre></td></tr></tbody></table></figure>
<p>在地址系统中，<code>postal_code</code>（邮政编码）字段可能用于以下场景：</p>
<ul>
<li>按邮政编码筛选地址。例如，在电商系统中，按邮政编码筛选用户地址，以确定是否支持配送</li>
<li>邮政编码的批量统计或区域分析，例如确定特定邮政编码区域的用户密度</li>
</ul>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@CreateDateColumn</span>()</span><br><span class="line"><span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br></pre></td></tr></tbody></table></figure>
<h2 id="39-库存日志"><a class="markdownIt-Anchor" href="#39-库存日志"></a> 3.9. 库存日志</h2>
<figure class="highlight ts"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Index</span>()</span><br><span class="line"><span class="meta">@CreateDateColumn</span>()</span><br><span class="line"><span class="attr">created_at</span>: <span class="title class_">Date</span>;</span><br></pre></td></tr></tbody></table></figure>
<p>接下来，我们可以使用以下命令生成数据库迁移文件：</p>
<figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">yarn migration:generate src/migrations/CreateIndex</span><br></pre></td></tr></tbody></table></figure>
<p>然后使用以下命令应用迁移并更新数据库：</p>
<figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">yarn migration:run</span><br></pre></td></tr></tbody></table></figure>
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