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diff --git a/2025/09/09/database-fk-design-in-clinical-medicine/index.html b/2025/09/09/database-fk-design-in-clinical-medicine/index.html index 04de22de..78b23495 100644 --- a/2025/09/09/database-fk-design-in-clinical-medicine/index.html +++ b/2025/09/09/database-fk-design-in-clinical-medicine/index.html @@ -245,7 +245,7 @@ <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> +<p>不过现代云医疗数据库（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> </div> @@ -2577,7 +2577,7 @@ await prisma.$transaction(async tx => { <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> +<p>不过现代云医疗数据库（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> @@ -5369,45 +5369,6 @@ 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>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> @@ -6675,6 +6636,45 @@ 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>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> |