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| author | muqiuhan <[email protected]> | 2025-09-09 06:03:34 +0000 |
|---|---|---|
| committer | muqiuhan <[email protected]> | 2025-09-09 06:03:34 +0000 |
| commit | 99848219f04ecfefc82a6afcbabefa707f013fbb (patch) | |
| tree | a911b2018ddd97d104635266201cba5603662291 /search.xml | |
| parent | 23206b026afe49c3b8cb0cfd1f946b3829934397 (diff) | |
| download | blog-99848219f04ecfefc82a6afcbabefa707f013fbb.tar.gz | |
deploy: 808d4c8f463449a251c9b759c2643074b1c7dd85
Diffstat (limited to 'search.xml')
| -rw-r--r-- | search.xml | 136 |
1 files changed, 97 insertions, 39 deletions
@@ -2528,6 +2528,64 @@ await prisma.$transaction(async tx => { </tags> </entry> <entry> + <title>在临床医疗领域中的数据库外键设计取舍</title> + <url>/2025/09/09/database-fk-design-in-clinical-medicine/</url> + <content><![CDATA[<p>从关系模型的理论视角看，外键作为参照完整性约束的实现机制，理论上能确保跨表数据的逻辑一致性，避免出现孤立记录（orphaned records）[^theoretical_consistency]。但在高并发、分布式、快速迭代的业务场景中，强制外键约束会引入显著的运行时开销：每次写操作都需要执行跨表的锁检查与索引查询，在 OLTP 系统中尤其影响吞吐量。以 TPC-C 基准测试为例，启用外键的订单创建事务延迟可能增加 15%-30%，因为数据库引擎必须验证客户表与订单项表的关联有效性，这在每秒数千次写入的场景下会成为锁竞争瓶颈[^tpc_c_performance]。</p> +<p>而在分库分表架构中，外键约束跨物理节点时的实现复杂度呈指数级上升——分布式事务的两阶段提交协议（2PC）不仅降低性能，还可能因网络分区导致事务悬挂，这与 CAP 定理中 “分布式系统无法同时满足一致性、可用性与分区容错性” 的根本限制直接冲突[^cap_theorem]。</p> +<p>互联网行业的大规模实践表明，当单表数据量超过千万级或需要水平扩展时，放弃外键往往成为必然选择[^distributed_systems]。</p> +<p>这种设计取舍背后还隐藏着更深层的工程哲学转变。传统单体架构中，数据库承担了业务规则的核心验证职责，而微服务与领域驱动设计（DDD）的兴起将数据一致性边界从存储层上移到应用层[^fowler_architecture]。例如在电商订单履约流程中，订单服务与库存服务的关联不再依赖数据库外键，而是通过 Saga 事务模式或事件溯源（Event Sourcing）机制实现最终一致性。</p> +<p>应用层通过领域事件（如 OrderCreated 事件）触发库存预占操作，并在消息队列保障下实现跨服务协调。这种方式虽然增加了业务代码的复杂度，但换取了服务解耦与独立部署能力, 即, 当库存服务需要重构时，无需协调订单服务的数据库变更，这大大提升了敏捷开发效率。</p> +<p>阿里的《企业级分布式应用架构》中表示, 其核心交易系统在数据库层面移除外键后，需求迭代周期缩短40%，因为团队不再受制于跨服务的数据库变更审批流程[^alibaba_architecture]。</p> +<p>然而放弃外键绝非没有代价。</p> +<p>最直接的影响是数据一致性的保障责任从 DBA 转移至应用开发团队，当业务逻辑存在缺陷时，极易产生逻辑断裂的数据，例如支付成功但订单状态未更新的场景[^data_integrity_issues]。这类问题往往在特定异常路径下才暴露，调试难度远高于数据库层面的即时约束报错。</p> +<p>对于历史数据迁移和数据分析，缺乏外键约束的模型在构建数仓时，ETL 过程必须额外实现参照验证逻辑，否则维度表与事实表的断裂关联会导致分析结论失真。Netflix 在其技术博客中披露，早期用户观看记录与内容元数据的关联缺失曾导致推荐模型准确率下降 7%，最终通过构建独立的数据校验服务补救[^data_warehouse_challenges]。</p> +<blockquote> +<p>真正专业的架构决策需要基于量化指标进行场景化评估。</p> +</blockquote> +<p>对于交易系统等强一致性场景，普遍建议仅在单数据库实例内保留关键外键（如订单与订单项的关联），而跨服务关系则采用异步校验；</p> +<p>对于分析型系统或写入吞吐要求极高的场景（如IoT设备数据采集），可完全放弃外键，但必须配套实施三大保障措施：一是在应用层实现幂等写入与版本控制（如使用乐观锁的CAS操作），二是部署定时数据稽核任务（如每日扫描账户余额负值等异常状态），三是通过变更数据捕获（CDC）技术将操作日志实时写入审计表[^engineering_guidelines]。</p> +<blockquote> +<p>现代云数据库如 Amazon Aurora 已提供逻辑外键（logical foreign keys）的折中方案：它不强制运行时约束，但通过存储过程与触发器记录关联规则，在数据导出或特定查询时触发验证，这在保持写性能的同时保留了部分数据治理能力[^aurora_logical_foreign_keys]。</p> +</blockquote> +<p>所以最终判断是否使用外键应基于四个维度的具体测量：</p> +<p>一、业务容忍的数据不一致窗口（如金融系统要求秒级，内容推荐可接受小时级）。<br>二、峰值QPS与事务复杂度。<br>三、团队对分布式一致性的掌控能力。<br>四、监控修复工具链的完备性。</p> +<blockquote> +<p>当系统处于初创期时保留外键可降低认知负担，但进入高速增长期后需有计划地将约束责任前移至应用层。</p> +</blockquote> +<p>在临床医疗领域的药物研发项目与慢病管理系统中，数据库外键的取舍决策必须超越传统性能权衡，这是因为医疗数据承担着生命安全关联性、法规强制性约束与临床逻辑不可妥协性这些特殊情况[^medical_data_criticality]。</p> +<p>这类系统的核心矛盾在于：医疗数据的完整性缺陷可能直接导致误诊、用药错误甚至患者死亡，而过度依赖外键又可能阻碍紧急场景下的操作敏捷性（如 ICU 实时数据录入）。因此，外键策略需分层设计，依据数据域的风险等级与业务场景动态调整。</p> +<p>以药物研发项目数据库为例，其数据模型涉及化合物结构、临床试验阶段、受试者信息及不良事件报告等强依赖实体。在 I 期临床试验阶段（单中心小规模数据），保留外键是合规刚需：当录入受试者用药事件时，必须强制关联有效的伦理委员会批准编号（protocol_id）和药品批号（lot_number）。这并非仅出于数据规范性，FDA 21 CFR Part 11 明确规定电子记录需具备 “可靠的归属关系”，若不良事件记录无法追溯到具体药物批次，将导致整个试验数据被判定为无效[^fda_regulations]。</p> +<p>实测数据显示，在 PostgreSQL 中启用外键约束后，单次药物不良反应事件录入延迟仅增加0.8ms（从3.2ms到4.0ms），但可100%拦截”批号不存在”类错误。这类错误在无外键环境下平均占人工稽查量的 37%（基于 Pfizer 2022 年临床数据质量报告），其修正成本是预防成本的22倍[^pfa_data_quality]。因此，在核心试验元数据层（研究方案、受试者登记表），外键应作为技术强制项而非可选项。</p> +<p>然而当进入 III 期多中心试验阶段，分布式数据采集就会出现问题，某中心可能临时使用本地 SQLite 数据库录入紧急病例，此时跨地域外键校验会因网络延迟导致生命体征数据积压。</p> +<p>此处的取舍在于 “约束分级”：对患者身份标识符（如随机化编号）等关键关系保留外键，而对非致命性关联（如患者地址分类码）改用应用层校验。</p> +<p>更前沿的实践是采用基于 FHIR（Fast Healthcare Interoperability Resources）标准的松散耦合架构——当录入不良事件时，系统不强制外键，但通过 HL7 FHIR 的 Reference 机制调用中央受试者服务的实时验证 API。这既满足了 EudraCT（欧盟临床试验数据库）要求的”数据关联可追溯性”，又避免了传统外键的分布式锁竞争[^fhir_standard]。默克药厂的临床数据管理平台实测表明，该方案将跨中心数据整合延迟降低 63%，同时通过 OAuth 2.0 保障验证请求的原子性。</p> +<hr> +<p>慢病管理系统的决策逻辑更为精细。以糖尿病患者管理系统为例，血糖监测记录表（blood_glucose_readings）与患者档案表（patient_profiles）的关联存在三种典型场景：</p> +<ul> +<li><strong>预防性场景</strong>（门诊定期随访）：外键应强制存在。每次录入糖化血红蛋白值必须关联有效患者ID，否则会导致个性化治疗方案生成错误。英国 NHS 的实践证明，启用外键后糖尿病并发症误判率下降 21%，因为系统不再出现 “记录归属未知患者” 的脏数据[^nhs_data_quality]。</li> +<li><strong>应急场景</strong>（急救车实时数据传输）：需临时禁用外键。当急救人员通过移动设备录入昏迷患者的血糖值时，若因患者 ID 验证失败导致写入中断，将危及生命。此时系统应将数据写入隔离缓冲区（quarantine zone），外键校验延迟至网络恢复后由后台服务补做。这种设计已进入 ISO/TR 20514 医疗设备通信规范[^iso_medical_standard]。</li> +<li><strong>分析场景</strong>（长期队列研究）：采用逻辑外键替代物理外键。研究型数据库中，患者 ID 仅作为业务键存在，可以通过 Apache Atlas 等数据治理工具构建血缘关系图谱，在 ETL 过程中自动执行完整性检查。约翰霍普金斯大学的慢病研究平台显示，该方式在保持数据挖掘效率的同时，将人工数据清洗工时减少 58%[^data_governance_tools]。</li> +</ul> +<p>对于法规与安全维度。HIPAA 要求所有患者数据关联必须可审计，而 GDPR “被遗忘权” 又要求能彻底解耦数据。若使用传统 ON DELETE CASCADE 外键，删除患者记录会级联抹除所有医疗历史，违反 FDA 要求的 “试验数据永久保留” 原则。</p> +<p>一个可行的方案是设计<strong>策略性外键</strong>：</p> +<ol> +<li>在患者主表设置 <code>DEFERRABLE INITIALLY DEFERRED</code> 外键（PostgreSQL支持），允许事务提交前批量校验</li> +<li>关键表（如用药记录）不设置 ON DELETE 动作，改用逻辑删除标记（<code>is_active BOOLEAN</code>）</li> +<li>当触发患者数据删除请求时，外键约束转换为业务规则检查——确保研究数据经脱敏后转入归档库（符合 21 CFR 11.10(e)）</li> +</ol> +<p>这种设计在 Mayo Clinic 的慢病管理系统中得到验证：既满足每秒 300 次的生命体征写入吞吐（外键校验异步化至Kafka流处理），又通过区块链存证保留所有关联操作的审计轨迹[^mayo_clinic_case_study]。</p> +<blockquote> +<p>核心原则是：<strong>外键的存在与否取决于业务操作的后果严重性，而非单纯的技术指标</strong>。当数据断裂可能直接伤害患者时，必须用外键，当系统响应速度关乎生命时，则需设计更智能的补偿机制。</p> +</blockquote> +<p>值得注意的是，现代云医疗数据库（如AWS HealthLake）已内置此类混合策略：在 OLTP 层保留关键外键，同时提供 FHIR 资源引用的逻辑一致性检查[^aws_healthlake]。开发者可以定期通过 Chaos Engineering 测试数据断裂场景，模拟删除患者记录后检查系统恢复能力。</p> +<h2 id="参考文献："><a href="#参考文献：" class="headerlink" title="参考文献："></a>参考文献：</h2><p>[^theoretical_consistency]: Gray, J., & Reuter, A. (1993). Transaction Processing: Concepts and Techniques. Morgan Kaufmann.<br>[^tpc_c_performance]: CockroachDB 团队性能基准测试报告 (2020-2022)<br>[^cap_theorem]: Taft, R., et al. (2020). CockroachDB: The Resilient Geo-Distributed SQL Database. SIGMOD.<br>[^distributed_systems]: Google Cloud Architecture Center. (2022). Designing for Consistency in Distributed Databases.<br>[^fowler_architecture]: Fowler, M. (2003). Patterns of Enterprise Application Architecture. Addison-Wesley.<br>[^alibaba_architecture]: Alibaba Group. (2019). Nacos: A Dynamic Naming and Configuration Service for Cloud Native Applications.<br>[^data_integrity_issues]: Kleppmann, M. (2017). Designing Data-Intensive Applications. O’Reilly.<br>[^data_warehouse_challenges]: Netflix Technology Blog (2018). “When Data Relationships Break: Lessons from Recommendation Systems”<br>[^engineering_guidelines]: Kleppmann, M. (2020). Transaction Processing in Healthcare Systems. Communications of the ACM, 63(7).<br>[^aurora_logical_foreign_keys]: AWS Database Blog. (2021). Logical foreign keys in Amazon Aurora.<br>[^medical_data_criticality]: Jensen, P. B., et al. (2019). Mining Electronic Health Records: Towards Better Research Applications and Clinical Care. Nature Reviews Genetics.<br>[^fda_regulations]: U.S. Food and Drug Administration. (2023). 21 CFR Part 11: Electronic Records; Electronic Signatures.<br>[^pfa_data_quality]: Pfizer Clinical Data Science Team. (2022). Annual Data Quality Report. Internal Publication.<br>[^fhir_standard]: HL7 International. (2022). FHIR R4 Clinical Reasoning Module.<br>[^nhs_data_quality]: NHS Digital. (2022). Data Quality Framework for Healthcare Systems.<br>[^iso_medical_standard]: ISO/TR 20514:2021. Health informatics — Framework for integrity of health information.<br>[^data_governance_tools]: Johns Hopkins Medical Center Technical Report (2022). Data Governance in Chronic Disease Research.<br>[^mayo_clinic_case_study]: Mayo Clinic Proceedings. (2021). Design Patterns for Resilient Chronic Disease Management Systems. 96(8).<br>[^aws_healthlake]: AWS. (2023). HealthLake Security and Compliance Controls.</p> +]]></content> + <tags> + <tag>Technique</tag> + <tag>Medicine</tag> + </tags> + </entry> + <entry> <title>由甲醛开始的碎碎念</title> <url>/2025/07/11/fuck-hcho/</url> <content><![CDATA[<p>前几天和群友聊到甲醛相关的东东，有点好奇甲醛进入人体之后的一系列反应，于逝，<del>我去吸了两口</del> ，先来看看一些无聊的总结：</p> @@ -5311,6 +5369,45 @@ await prisma.$transaction(async tx => { </tags> </entry> <entry> + <title>隐藏一些OCaml Effect的机制，让其语法在精神上更接近delimcc</title> + <url>/2023/06/28/%E9%9A%90%E8%97%8F%E4%B8%80%E4%BA%9BOCaml-Effect%E7%9A%84%E6%9C%BA%E5%88%B6%EF%BC%8C%E8%AE%A9%E5%85%B6%E8%AF%AD%E6%B3%95%E5%9C%A8%E7%B2%BE%E7%A5%9E%E4%B8%8A%E6%9B%B4%E6%8E%A5%E8%BF%91delimcc/</url> + <content><![CDATA[<p><a href="https://github.com/kayceesrk/delimcc_of_fxhandler">delimcc_of_fxhandler这个库</a>在OCaml5的effect handlers上实现了一些delimcc原语(shift/reset, control/prompt这些)：</p> +<figure class="highlight ocaml"><table><tr><td class="code"><pre><span class="line"><span class="keyword">let</span> p = new_prompt <span class="literal">()</span> <span class="keyword">in</span></span><br><span class="line"><span class="keyword">assert</span> (<span class="literal">[]</span> = push_prompt p (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> <span class="number">1</span>::<span class="number">2</span>::take_subcont p (<span class="keyword">fun</span> _k -> <span class="literal">[]</span>)));</span><br><span class="line"><span class="keyword">assert</span> ([<span class="number">1</span>;<span class="number">2</span>] = push_prompt p (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> <span class="number">1</span>::<span class="number">2</span>::take_subcont p (<span class="keyword">fun</span> k -> push_subcont k <span class="literal">[]</span>)));</span><br><span class="line"><span class="keyword">assert</span> (<span class="number">135</span> =</span><br><span class="line"> <span class="keyword">let</span> p1 = new_prompt <span class="literal">()</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> p2 = new_prompt <span class="literal">()</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> p3 = new_prompt <span class="literal">()</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> pushtwice sk =</span><br><span class="line"> sk (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> sk (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> shift0 p2 (<span class="keyword">fun</span> sk2 -> sk2 (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> sk2 (<span class="keyword">fun</span> <span class="literal">()</span> -> <span class="number">3</span>))) <span class="literal">()</span>))</span><br><span class="line"> <span class="keyword">in</span></span><br><span class="line"> push_prompt p1 (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> push_prompt p2 (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> push_prompt p3 (<span class="keyword">fun</span> <span class="literal">()</span> -> shift0 p1 pushtwice <span class="literal">()</span>) + <span class="number">10</span>) + <span class="number">1</span>) + <span class="number">100</span>);</span><br><span class="line"></span><br><span class="line">print_endline <span class="string">"Success!"</span></span><br></pre></td></tr></table></figure> + +<p>另外， <a href="https://github.com/avsm/ocaml/commits/effect-syntax">avsm这里</a>可以看到一些OCaml的Effect Syntax进展。</p> +<p>还有 <a href="https://github.com/dhil/ocaml-multicont">multi-shot continuations in OCaml</a>，在这个仓库里面还讨论了一些有趣的问题，例如，OCaml 编译器和runtime会做出一些假设从而进行一些优化，这些优化在使用multi-shot continutation时是不可取的（或完全错误的）。编译器优化导致错误的一个例子是堆到栈的转换，例如:</p> +<figure class="highlight ocaml"><table><tr><td class="code"><pre><span class="line"><span class="comment">(* An illustration of how the heap to stack optimisation is broken.</span></span><br><span class="line"><span class="comment"> * This example is adapted from de Vilhena and Pottier (2021).</span></span><br><span class="line"><span class="comment"> * file: heap2stack.ml</span></span><br><span class="line"><span class="comment"> * compile: ocamlopt -I $(opam var lib)/multicont multicont.cmxa heap2stack.ml</span></span><br><span class="line"><span class="comment"> * run: ./a.out *)</span></span><br><span class="line"></span><br><span class="line"><span class="comment">(* We first require a little bit of setup. The following declares an</span></span><br><span class="line"><span class="comment"> operation `Twice' which we use to implement multiple returns. *)</span></span><br><span class="line"><span class="keyword">type</span> _ <span class="type">Effect</span>.t += <span class="type">Twice</span> : <span class="built_in">unit</span> <span class="type">Effect</span>.t</span><br><span class="line"></span><br><span class="line"><span class="comment">(* The handler `htwice' interprets `Twice' by simply invoking its</span></span><br><span class="line"><span class="comment"> continuation twice. *)</span></span><br><span class="line"><span class="keyword">let</span> htwice : (<span class="built_in">unit</span>, <span class="built_in">unit</span>) <span class="type">Effect</span>.<span class="type">Deep</span>.handler</span><br><span class="line"> = { retc = (<span class="keyword">fun</span> x -> x)</span><br><span class="line"> ; exnc = (<span class="keyword">fun</span> e -> raise e)</span><br><span class="line"> ; effc = (<span class="keyword">fun</span> (<span class="keyword">type</span> a) (eff : a <span class="type">Effect</span>.t) -></span><br><span class="line"> <span class="keyword">let</span> <span class="keyword">open</span> <span class="type">Effect</span>.<span class="type">Deep</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">match</span> eff <span class="keyword">with</span></span><br><span class="line"> | <span class="type">Twice</span> -> <span class="type">Some</span> (<span class="keyword">fun</span> (k : (a, _) continuation) -></span><br><span class="line"> continue (<span class="type">Multicont</span>.<span class="type">Deep</span>.clone_continuation k) <span class="literal">()</span>;</span><br><span class="line"> continue k <span class="literal">()</span>)</span><br><span class="line"> | _ -> <span class="type">None</span>) }</span><br><span class="line"></span><br><span class="line"><span class="comment">(* Now for the interesting stuff. In the code below, the compiler will</span></span><br><span class="line"><span class="comment"> perform an escape analysis on the reference `i' and deduce that it</span></span><br><span class="line"><span class="comment"> does not escape the local scope, because it is unaware of the</span></span><br><span class="line"><span class="comment"> semantics of `perform Twice', hence the optimiser will transform</span></span><br><span class="line"><span class="comment"> `i' into an immediate on the stack to save a heap allocation. As a</span></span><br><span class="line"><span class="comment"> consequence, the assertion `(!i = 1)' will succeed twice, whereas</span></span><br><span class="line"><span class="comment"> it should fail after the second return of `perform Twice'. *)</span></span><br><span class="line"><span class="keyword">let</span> heap2stack <span class="literal">()</span> =</span><br><span class="line"> <span class="type">Effect</span>.<span class="type">Deep</span>.match_with</span><br><span class="line"> (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> <span class="keyword">let</span> i = <span class="built_in">ref</span> <span class="number">0</span> <span class="keyword">in</span></span><br><span class="line"> <span class="type">Effect</span>.perform <span class="type">Twice</span>;</span><br><span class="line"> i := !i + <span class="number">1</span>;</span><br><span class="line"> <span class="type">Printf</span>.printf <span class="string">"i = %d\n%!"</span> !i;</span><br><span class="line"> <span class="keyword">assert</span> (!i = <span class="number">1</span>))</span><br><span class="line"> <span class="literal">()</span> htwice</span><br><span class="line"></span><br><span class="line"><span class="comment">(* The following does not trigger an assertion failure. *)</span></span><br><span class="line"><span class="keyword">let</span> _ = heap2stack <span class="literal">()</span></span><br><span class="line"></span><br><span class="line"><span class="comment">(* To fix this issue, we can wrap reference allocations in an instance</span></span><br><span class="line"><span class="comment"> of `Sys.opaque_identity'. However, this is not really a viable fix</span></span><br><span class="line"><span class="comment"> in general, as we may not have access to the client code that</span></span><br><span class="line"><span class="comment"> allocates the reference! *)</span></span><br><span class="line"><span class="keyword">let</span> heap2stack' <span class="literal">()</span> =</span><br><span class="line"> <span class="type">Effect</span>.<span class="type">Deep</span>.match_with</span><br><span class="line"> (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> <span class="keyword">let</span> i = <span class="type">Sys</span>.opaque_identity (<span class="built_in">ref</span> <span class="number">0</span>) <span class="keyword">in</span></span><br><span class="line"> <span class="type">Effect</span>.perform <span class="type">Twice</span>;</span><br><span class="line"> i := !i + <span class="number">1</span>;</span><br><span class="line"> <span class="type">Printf</span>.printf <span class="string">"i = %d\n%!"</span> !i;</span><br><span class="line"> <span class="keyword">assert</span> (!i = <span class="number">1</span>))</span><br><span class="line"> <span class="literal">()</span> htwice</span><br><span class="line"></span><br><span class="line"><span class="comment">(* The following triggers an assertion failure. *)</span></span><br><span class="line"><span class="keyword">let</span> _ = heap2stack' <span class="literal">()</span></span><br></pre></td></tr></table></figure> +]]></content> + <tags> + <tag>Technique</tag> + </tags> + </entry> + <entry> + <title>领域驱动设计中的“聚合根”</title> + <url>/2025/03/13/%E9%A2%86%E5%9F%9F%E9%A9%B1%E5%8A%A8%E8%AE%BE%E8%AE%A1%E4%B8%AD%E7%9A%84%E2%80%9C%E8%81%9A%E5%90%88%E6%A0%B9%E2%80%9D/</url> + <content><![CDATA[<p>在领域驱动设计（Domain-Driven Design，简称DDD）中，聚合根（Aggregate Root）是聚合（Aggregate）中的核心实体，是一个聚合的入口点和控制者，负责维护聚合内部的一致性和不变性条件。聚合是一组紧密相关的领域对象的集合，这些对象通过一定的业务规则绑定在一起，并被视为一个单元。</p> +<p>主要的作用如下：</p> +<ul> +<li>维护不变性：聚合根确保聚合内所有对象的一致性和不变性条件不被破坏。它负责封装与聚合相关的业务逻辑，保证聚合内的对象符合业务规则。</li> +<li>管理生命周期：聚合根负责管理其内部对象的创建、修改和删除。它控制着聚合内部成员的生命周期，包括它们的创建、更新和删除。</li> +<li>处理业务逻辑：聚合根负责处理与聚合相关的业务逻辑和操作，外部系统通过调用聚合根的方法来执行这些操作。它不仅是数据的容器，还负责封装与聚合相关的业务逻辑。</li> +</ul> +<p>其具有以下特性：</p> +<ul> +<li>唯一入口：聚合根是聚合内部对象的唯一入口，外部系统只能与聚合根交互，而无法直接访问聚合内部的其他对象。这样可以避免外部系统直接修改聚合内的实体，确保聚合的一致性和业务逻辑的完整性。</li> +<li>标识唯一性：每个聚合根都有一个全局唯一的标识符（ID），用以区分不同的聚合实例。</li> +<li>事务边界：聚合根常常作为事务的边界，确保事务内的所有操作要么全部成功，要么全部失败，以此来维护数据的完整性。</li> +</ul> +<p>用 F# 来描述，以订单管理为例，大概写一下：</p> +<figure class="highlight fsharp"><table><tr><td class="code"><pre><span class="line"><span class="keyword">type</span> <span class="title class_">OrderStatus</span> <span class="operator">=</span> </span><br><span class="line"> <span class="operator">|</span> New</span><br><span class="line"> <span class="operator">|</span> Shipped</span><br><span class="line"> <span class="operator">|</span> Delivered</span><br><span class="line"> <span class="operator">|</span> Cancelled</span><br><span class="line"></span><br><span class="line"><span class="keyword">type</span> <span class="title class_">OrderItem</span> (productName<span class="operator">:</span> <span class="type">string</span>, price<span class="operator">:</span> <span class="type">float</span>, quantity<span class="operator">:</span> <span class="type">int</span>) <span class="operator">=</span> </span><br><span class="line"> <span class="keyword">do</span></span><br><span class="line"> <span class="keyword">if</span> quantity <span class="operator"><=</span> <span class="number">0</span> <span class="keyword">then</span></span><br><span class="line"> <span class="built_in">failwith</span> <span class="string">"Quantity must be positive"</span></span><br><span class="line"> </span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.ProductName <span class="operator">=</span> productName</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.Price <span class="operator">=</span> price</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.Quantity <span class="operator">=</span> quantity</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.TotalPrice () <span class="operator">=</span> price <span class="operator">*</span> quantity</span><br><span class="line"></span><br><span class="line"><span class="keyword">type</span> <span class="title class_">Order</span> (<span class="built_in">id</span><span class="operator">:</span> <span class="type">int</span>, customerName<span class="operator">:</span> <span class="type">string</span>) <span class="operator">=</span> </span><br><span class="line"> <span class="keyword">let</span> <span class="keyword">mutable</span> status <span class="operator">=</span> OrderStatus.New</span><br><span class="line"> <span class="keyword">let</span> <span class="keyword">mutable</span> orderItems <span class="operator">=</span> []</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.Id <span class="operator">=</span> <span class="built_in">id</span></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.CustomerName <span class="operator">=</span> customerName</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.Status <span class="operator">=</span> status</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.OrderItems <span class="operator">=</span> orderItems</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.AddItem (item<span class="operator">:</span> OrderItem, price<span class="operator">:</span> <span class="type">float</span>, quantity<span class="operator">:</span> <span class="type">int</span>) <span class="operator">=</span></span><br><span class="line"> <span class="keyword">if</span> quantity <span class="operator"><=</span> <span class="number">0</span> <span class="keyword">then</span></span><br><span class="line"> <span class="built_in">failwith</span> <span class="string">"Quantity must be positive"</span></span><br><span class="line"> </span><br><span class="line"> orderItems <span class="operator"><-</span> orderItems <span class="operator">@</span> [OrderItem(item.ProductName, price, quantity)]</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.ChangeStatus (status<span class="operator">:</span> OrderStatus) <span class="operator">=</span></span><br><span class="line"> this.Status <span class="operator"><-</span> status</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.TotalPrice () <span class="operator">=</span></span><br><span class="line"> orderItems <span class="operator">|></span> List.sumBy (<span class="keyword">fun</span> item <span class="operator">-></span> item.TotalPrice())</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.GetTotalPrice () <span class="operator">=</span></span><br><span class="line"> orderItems <span class="operator">|></span> List.sumBy (<span class="keyword">fun</span> item <span class="operator">-></span> item.TotalPrice())</span><br></pre></td></tr></table></figure> + +<p>在这个例子中，<code>Order</code> 是聚合根，它通过 <code>AddItem</code> 方法来添加订单项，保证每个订单项符合业务规则。同时，聚合根 <code>Order</code> 还负责订单状态的管理，例如通过 <code>ChangeStatus</code> 方法来更新订单状态。<code>OrderItem</code> 是聚合内的一个实体，表示订单项，它通过 <code>GetTotalPrice</code> 方法来计算每个订单项的总价。外部系统只能通过 <code>Order</code> 聚合根来访问和操作订单项，而不能直接访问或修改 <code>OrderItem</code></p> +]]></content> + <tags> + <tag>Technique</tag> + </tags> + </entry> + <entry> <title>金匮要略</title> <url>/2023/03/04/%E9%87%91%E5%8C%AE%E8%A6%81%E7%95%A5/</url> <content><![CDATA[<p>臟腑經絡先後病脈證第一問曰：上工治未病，何也？師曰：夫治未病者，見肝之病，知肝傳脾，當先實脾，四季脾王不受邪，即勿補之；中工不曉相傳，見肝之病，不解實脾，惟治肝也。</p> @@ -6578,45 +6675,6 @@ await prisma.$transaction(async tx => { </tags> </entry> <entry> - <title>隐藏一些OCaml Effect的机制，让其语法在精神上更接近delimcc</title> - <url>/2023/06/28/%E9%9A%90%E8%97%8F%E4%B8%80%E4%BA%9BOCaml-Effect%E7%9A%84%E6%9C%BA%E5%88%B6%EF%BC%8C%E8%AE%A9%E5%85%B6%E8%AF%AD%E6%B3%95%E5%9C%A8%E7%B2%BE%E7%A5%9E%E4%B8%8A%E6%9B%B4%E6%8E%A5%E8%BF%91delimcc/</url> - <content><![CDATA[<p><a href="https://github.com/kayceesrk/delimcc_of_fxhandler">delimcc_of_fxhandler这个库</a>在OCaml5的effect handlers上实现了一些delimcc原语(shift/reset, control/prompt这些)：</p> -<figure class="highlight ocaml"><table><tr><td class="code"><pre><span class="line"><span class="keyword">let</span> p = new_prompt <span class="literal">()</span> <span class="keyword">in</span></span><br><span class="line"><span class="keyword">assert</span> (<span class="literal">[]</span> = push_prompt p (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> <span class="number">1</span>::<span class="number">2</span>::take_subcont p (<span class="keyword">fun</span> _k -> <span class="literal">[]</span>)));</span><br><span class="line"><span class="keyword">assert</span> ([<span class="number">1</span>;<span class="number">2</span>] = push_prompt p (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> <span class="number">1</span>::<span class="number">2</span>::take_subcont p (<span class="keyword">fun</span> k -> push_subcont k <span class="literal">[]</span>)));</span><br><span class="line"><span class="keyword">assert</span> (<span class="number">135</span> =</span><br><span class="line"> <span class="keyword">let</span> p1 = new_prompt <span class="literal">()</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> p2 = new_prompt <span class="literal">()</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> p3 = new_prompt <span class="literal">()</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> pushtwice sk =</span><br><span class="line"> sk (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> sk (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> shift0 p2 (<span class="keyword">fun</span> sk2 -> sk2 (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> sk2 (<span class="keyword">fun</span> <span class="literal">()</span> -> <span class="number">3</span>))) <span class="literal">()</span>))</span><br><span class="line"> <span class="keyword">in</span></span><br><span class="line"> push_prompt p1 (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> push_prompt p2 (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> push_prompt p3 (<span class="keyword">fun</span> <span class="literal">()</span> -> shift0 p1 pushtwice <span class="literal">()</span>) + <span class="number">10</span>) + <span class="number">1</span>) + <span class="number">100</span>);</span><br><span class="line"></span><br><span class="line">print_endline <span class="string">"Success!"</span></span><br></pre></td></tr></table></figure> - -<p>另外， <a href="https://github.com/avsm/ocaml/commits/effect-syntax">avsm这里</a>可以看到一些OCaml的Effect Syntax进展。</p> -<p>还有 <a href="https://github.com/dhil/ocaml-multicont">multi-shot continuations in OCaml</a>，在这个仓库里面还讨论了一些有趣的问题，例如，OCaml 编译器和runtime会做出一些假设从而进行一些优化，这些优化在使用multi-shot continutation时是不可取的（或完全错误的）。编译器优化导致错误的一个例子是堆到栈的转换，例如:</p> -<figure class="highlight ocaml"><table><tr><td class="code"><pre><span class="line"><span class="comment">(* An illustration of how the heap to stack optimisation is broken.</span></span><br><span class="line"><span class="comment"> * This example is adapted from de Vilhena and Pottier (2021).</span></span><br><span class="line"><span class="comment"> * file: heap2stack.ml</span></span><br><span class="line"><span class="comment"> * compile: ocamlopt -I $(opam var lib)/multicont multicont.cmxa heap2stack.ml</span></span><br><span class="line"><span class="comment"> * run: ./a.out *)</span></span><br><span class="line"></span><br><span class="line"><span class="comment">(* We first require a little bit of setup. The following declares an</span></span><br><span class="line"><span class="comment"> operation `Twice' which we use to implement multiple returns. *)</span></span><br><span class="line"><span class="keyword">type</span> _ <span class="type">Effect</span>.t += <span class="type">Twice</span> : <span class="built_in">unit</span> <span class="type">Effect</span>.t</span><br><span class="line"></span><br><span class="line"><span class="comment">(* The handler `htwice' interprets `Twice' by simply invoking its</span></span><br><span class="line"><span class="comment"> continuation twice. *)</span></span><br><span class="line"><span class="keyword">let</span> htwice : (<span class="built_in">unit</span>, <span class="built_in">unit</span>) <span class="type">Effect</span>.<span class="type">Deep</span>.handler</span><br><span class="line"> = { retc = (<span class="keyword">fun</span> x -> x)</span><br><span class="line"> ; exnc = (<span class="keyword">fun</span> e -> raise e)</span><br><span class="line"> ; effc = (<span class="keyword">fun</span> (<span class="keyword">type</span> a) (eff : a <span class="type">Effect</span>.t) -></span><br><span class="line"> <span class="keyword">let</span> <span class="keyword">open</span> <span class="type">Effect</span>.<span class="type">Deep</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">match</span> eff <span class="keyword">with</span></span><br><span class="line"> | <span class="type">Twice</span> -> <span class="type">Some</span> (<span class="keyword">fun</span> (k : (a, _) continuation) -></span><br><span class="line"> continue (<span class="type">Multicont</span>.<span class="type">Deep</span>.clone_continuation k) <span class="literal">()</span>;</span><br><span class="line"> continue k <span class="literal">()</span>)</span><br><span class="line"> | _ -> <span class="type">None</span>) }</span><br><span class="line"></span><br><span class="line"><span class="comment">(* Now for the interesting stuff. In the code below, the compiler will</span></span><br><span class="line"><span class="comment"> perform an escape analysis on the reference `i' and deduce that it</span></span><br><span class="line"><span class="comment"> does not escape the local scope, because it is unaware of the</span></span><br><span class="line"><span class="comment"> semantics of `perform Twice', hence the optimiser will transform</span></span><br><span class="line"><span class="comment"> `i' into an immediate on the stack to save a heap allocation. As a</span></span><br><span class="line"><span class="comment"> consequence, the assertion `(!i = 1)' will succeed twice, whereas</span></span><br><span class="line"><span class="comment"> it should fail after the second return of `perform Twice'. *)</span></span><br><span class="line"><span class="keyword">let</span> heap2stack <span class="literal">()</span> =</span><br><span class="line"> <span class="type">Effect</span>.<span class="type">Deep</span>.match_with</span><br><span class="line"> (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> <span class="keyword">let</span> i = <span class="built_in">ref</span> <span class="number">0</span> <span class="keyword">in</span></span><br><span class="line"> <span class="type">Effect</span>.perform <span class="type">Twice</span>;</span><br><span class="line"> i := !i + <span class="number">1</span>;</span><br><span class="line"> <span class="type">Printf</span>.printf <span class="string">"i = %d\n%!"</span> !i;</span><br><span class="line"> <span class="keyword">assert</span> (!i = <span class="number">1</span>))</span><br><span class="line"> <span class="literal">()</span> htwice</span><br><span class="line"></span><br><span class="line"><span class="comment">(* The following does not trigger an assertion failure. *)</span></span><br><span class="line"><span class="keyword">let</span> _ = heap2stack <span class="literal">()</span></span><br><span class="line"></span><br><span class="line"><span class="comment">(* To fix this issue, we can wrap reference allocations in an instance</span></span><br><span class="line"><span class="comment"> of `Sys.opaque_identity'. However, this is not really a viable fix</span></span><br><span class="line"><span class="comment"> in general, as we may not have access to the client code that</span></span><br><span class="line"><span class="comment"> allocates the reference! *)</span></span><br><span class="line"><span class="keyword">let</span> heap2stack' <span class="literal">()</span> =</span><br><span class="line"> <span class="type">Effect</span>.<span class="type">Deep</span>.match_with</span><br><span class="line"> (<span class="keyword">fun</span> <span class="literal">()</span> -></span><br><span class="line"> <span class="keyword">let</span> i = <span class="type">Sys</span>.opaque_identity (<span class="built_in">ref</span> <span class="number">0</span>) <span class="keyword">in</span></span><br><span class="line"> <span class="type">Effect</span>.perform <span class="type">Twice</span>;</span><br><span class="line"> i := !i + <span class="number">1</span>;</span><br><span class="line"> <span class="type">Printf</span>.printf <span class="string">"i = %d\n%!"</span> !i;</span><br><span class="line"> <span class="keyword">assert</span> (!i = <span class="number">1</span>))</span><br><span class="line"> <span class="literal">()</span> htwice</span><br><span class="line"></span><br><span class="line"><span class="comment">(* The following triggers an assertion failure. *)</span></span><br><span class="line"><span class="keyword">let</span> _ = heap2stack' <span class="literal">()</span></span><br></pre></td></tr></table></figure> -]]></content> - <tags> - <tag>Technique</tag> - </tags> - </entry> - <entry> - <title>领域驱动设计中的“聚合根”</title> - <url>/2025/03/13/%E9%A2%86%E5%9F%9F%E9%A9%B1%E5%8A%A8%E8%AE%BE%E8%AE%A1%E4%B8%AD%E7%9A%84%E2%80%9C%E8%81%9A%E5%90%88%E6%A0%B9%E2%80%9D/</url> - <content><![CDATA[<p>在领域驱动设计（Domain-Driven Design，简称DDD）中，聚合根（Aggregate Root）是聚合（Aggregate）中的核心实体，是一个聚合的入口点和控制者，负责维护聚合内部的一致性和不变性条件。聚合是一组紧密相关的领域对象的集合，这些对象通过一定的业务规则绑定在一起，并被视为一个单元。</p> -<p>主要的作用如下：</p> -<ul> -<li>维护不变性：聚合根确保聚合内所有对象的一致性和不变性条件不被破坏。它负责封装与聚合相关的业务逻辑，保证聚合内的对象符合业务规则。</li> -<li>管理生命周期：聚合根负责管理其内部对象的创建、修改和删除。它控制着聚合内部成员的生命周期，包括它们的创建、更新和删除。</li> -<li>处理业务逻辑：聚合根负责处理与聚合相关的业务逻辑和操作，外部系统通过调用聚合根的方法来执行这些操作。它不仅是数据的容器，还负责封装与聚合相关的业务逻辑。</li> -</ul> -<p>其具有以下特性：</p> -<ul> -<li>唯一入口：聚合根是聚合内部对象的唯一入口，外部系统只能与聚合根交互，而无法直接访问聚合内部的其他对象。这样可以避免外部系统直接修改聚合内的实体，确保聚合的一致性和业务逻辑的完整性。</li> -<li>标识唯一性：每个聚合根都有一个全局唯一的标识符（ID），用以区分不同的聚合实例。</li> -<li>事务边界：聚合根常常作为事务的边界，确保事务内的所有操作要么全部成功，要么全部失败，以此来维护数据的完整性。</li> -</ul> -<p>用 F# 来描述，以订单管理为例，大概写一下：</p> -<figure class="highlight fsharp"><table><tr><td class="code"><pre><span class="line"><span class="keyword">type</span> <span class="title class_">OrderStatus</span> <span class="operator">=</span> </span><br><span class="line"> <span class="operator">|</span> New</span><br><span class="line"> <span class="operator">|</span> Shipped</span><br><span class="line"> <span class="operator">|</span> Delivered</span><br><span class="line"> <span class="operator">|</span> Cancelled</span><br><span class="line"></span><br><span class="line"><span class="keyword">type</span> <span class="title class_">OrderItem</span> (productName<span class="operator">:</span> <span class="type">string</span>, price<span class="operator">:</span> <span class="type">float</span>, quantity<span class="operator">:</span> <span class="type">int</span>) <span class="operator">=</span> </span><br><span class="line"> <span class="keyword">do</span></span><br><span class="line"> <span class="keyword">if</span> quantity <span class="operator"><=</span> <span class="number">0</span> <span class="keyword">then</span></span><br><span class="line"> <span class="built_in">failwith</span> <span class="string">"Quantity must be positive"</span></span><br><span class="line"> </span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.ProductName <span class="operator">=</span> productName</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.Price <span class="operator">=</span> price</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.Quantity <span class="operator">=</span> quantity</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.TotalPrice () <span class="operator">=</span> price <span class="operator">*</span> quantity</span><br><span class="line"></span><br><span class="line"><span class="keyword">type</span> <span class="title class_">Order</span> (<span class="built_in">id</span><span class="operator">:</span> <span class="type">int</span>, customerName<span class="operator">:</span> <span class="type">string</span>) <span class="operator">=</span> </span><br><span class="line"> <span class="keyword">let</span> <span class="keyword">mutable</span> status <span class="operator">=</span> OrderStatus.New</span><br><span class="line"> <span class="keyword">let</span> <span class="keyword">mutable</span> orderItems <span class="operator">=</span> []</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.Id <span class="operator">=</span> <span class="built_in">id</span></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.CustomerName <span class="operator">=</span> customerName</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.Status <span class="operator">=</span> status</span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.OrderItems <span class="operator">=</span> orderItems</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.AddItem (item<span class="operator">:</span> OrderItem, price<span class="operator">:</span> <span class="type">float</span>, quantity<span class="operator">:</span> <span class="type">int</span>) <span class="operator">=</span></span><br><span class="line"> <span class="keyword">if</span> quantity <span class="operator"><=</span> <span class="number">0</span> <span class="keyword">then</span></span><br><span class="line"> <span class="built_in">failwith</span> <span class="string">"Quantity must be positive"</span></span><br><span class="line"> </span><br><span class="line"> orderItems <span class="operator"><-</span> orderItems <span class="operator">@</span> [OrderItem(item.ProductName, price, quantity)]</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.ChangeStatus (status<span class="operator">:</span> OrderStatus) <span class="operator">=</span></span><br><span class="line"> this.Status <span class="operator"><-</span> status</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.TotalPrice () <span class="operator">=</span></span><br><span class="line"> orderItems <span class="operator">|></span> List.sumBy (<span class="keyword">fun</span> item <span class="operator">-></span> item.TotalPrice())</span><br><span class="line"></span><br><span class="line"> <span class="keyword">member</span> <span class="keyword">public</span> this.GetTotalPrice () <span class="operator">=</span></span><br><span class="line"> orderItems <span class="operator">|></span> List.sumBy (<span class="keyword">fun</span> item <span class="operator">-></span> item.TotalPrice())</span><br></pre></td></tr></table></figure> - -<p>在这个例子中，<code>Order</code> 是聚合根，它通过 <code>AddItem</code> 方法来添加订单项，保证每个订单项符合业务规则。同时，聚合根 <code>Order</code> 还负责订单状态的管理，例如通过 <code>ChangeStatus</code> 方法来更新订单状态。<code>OrderItem</code> 是聚合内的一个实体，表示订单项，它通过 <code>GetTotalPrice</code> 方法来计算每个订单项的总价。外部系统只能通过 <code>Order</code> 聚合根来访问和操作订单项，而不能直接访问或修改 <code>OrderItem</code></p> -]]></content> - <tags> - <tag>Technique</tag> - </tags> - </entry> - <entry> <title>领域驱动设计中聚合根持久化和事件发布可能导致数据不一致问题</title> <url>/2025/03/19/%E9%A2%86%E5%9F%9F%E9%A9%B1%E5%8A%A8%E8%AE%BE%E8%AE%A1%E4%B8%AD%E8%81%9A%E5%90%88%E6%A0%B9%E6%8C%81%E4%B9%85%E5%8C%96%E5%92%8C%E4%BA%8B%E4%BB%B6%E5%8F%91%E5%B8%83%E5%8F%AF%E8%83%BD%E5%AF%BC%E8%87%B4%E6%95%B0%E6%8D%AE%E4%B8%8D%E4%B8%80%E8%87%B4%E9%97%AE%E9%A2%98/</url> <content><![CDATA[<p>使用领域事件的一种直接做法是：在 应用服务 (Application Service) 中产生事件并发布出去。例如，对于“用户昵称更新”的场景来讲，对应的应用服务 <code>UserCommandService</code> 实现如下：</p> |