Altitude 2: Component

Altitude 2 — Component

Primary sources: Fowler (PoEAA + bliki) and Robert C. Martin (SOLID), both listed in full above.

• Dependency Injection / Inversion of Control — Fowler, "…the Dependency Injection pattern" (2004). https://martinfowler.com/articles/injection.html The "D" in SOLID (Robert C. Martin). The order service receives an IPaymentGateway, never constructs one. In C#: Microsoft.Extensions.DependencyInjection.
• Data Gateway (Table Data Gateway / Row Data Gateway) — Fowler, PoEAA. https://martinfowler.com/eaaCatalog/tableDataGateway.html OrderGateway and MenuGateway over stored procedures: the anchor for the book's SQL-first, anti-ORM stance. Contrast Data Mapper (https://martinfowler.com/eaaCatalog/dataMapper.html), which is what an ORM like EF implements.
• Ports & Adapters (Hexagonal Architecture) — Alistair Cockburn, 2005. https://alistair.cockburn.us/hexagonal-architecture/ Cousins: Robert C. Martin's Clean Architecture and Onion; we teach the minimal form, order domain at the centre.
• Pipeline / Middleware — Chain of Responsibility (GoF) at the object level; concretely, ASP.NET Core middleware that resolves tenant_id on every request. https://learn.microsoft.com/aspnet/core/fundamentals/middleware/
• Mediator — GoF Mediator at the object level; at the application level, the MediatR library by Jimmy Bogard. https://github.com/jbogard/MediatR A PlaceOrder request routed to its handler. The two are distinct; cite accordingly.
• Anti-Corruption Layer — Evans, Domain-Driven Design (2003). Summary: https://learn.microsoft.com/azure/architecture/patterns/anti-corruption-layer The higher-altitude cousin of Adapter; here it insulates the order model from a legacy restaurant POS.
• Domain Events — Evans (DDD); Fowler bliki. https://martinfowler.com/eaaDev/DomainEvent.html OrderPlaced fans out to kitchen, stock, and confirmation; in C#, often dispatched via MediatR INotification.
• Specification — Evans, Domain-Driven Design (2003); Evans & Fowler, "Specifications" (2002). https://www.martinfowler.com/apsupp/spec.pdf A composable business rule (IsSatisfiedBy) whose And/Or/Not combinators are a Composite; here "restaurant open and within range," reused across the search query, the order validation, and the UI.
• Honorable mentions — Result / ErrorOr functional error handling; plain Layered architecture.

Altitude 3 — Data & Persistence

Primary sources: Fowler (PoEAA + bliki) for the read/write-split combo and concurrency; the cloud catalogue for the rest.

• Multitenancy — recommended default: shared schema + tenant discriminator (tenant_id, where the restaurant/brand is the tenant) + Row-Level Security.

- Microsoft, Multitenant SaaS database tenancy patterns. https://learn.microsoft.com/azure/azure-sql/database/saas-tenancy-app-design-patterns The database-per-tenant / schema-per-tenant / shared-schema spectrum. - PostgreSQL, Row Security Policies (RLS). https://www.postgresql.org/docs/current/ddl-rowsecurity.html The mechanism that turns shared-schema isolation by tenant_id into a database guarantee.

• Event Sourcing — Fowler bliki. https://martinfowler.com/eaaDev/EventSourcing.html Popularised by Greg Young. The order is an append-only event stream.
• CQRS — Greg Young and Udi Dahan; Fowler bliki. https://martinfowler.com/bliki/CQRS.html The umbrella separating the order write model from its read views. The book's heaviest skip-if; pair the power with the cost caveat.
• Materialized View — Azure Cloud Design Patterns. https://learn.microsoft.com/azure/architecture/patterns/materialized-view The read models in the golden combo: courier task-list, customer order-history, restaurant live-board.
• Optimistic Concurrency (Optimistic Offline Lock) — Fowler, PoEAA. https://martinfowler.com/eaaCatalog/optimisticOfflineLock.html Rowversion / xmin / ETag; stops two menu edits from clobbering each other.
• Evolutionary Database Design / migrations — Fowler & Sadalage, "Evolutionary Database Design." https://martinfowler.com/articles/evodb.html Versioned, forward-only migrations for the orders schema (DbUp / Flyway-style; not EF migrations).
• Sharding / Partitioning — Azure Cloud Design Patterns. https://learn.microsoft.com/azure/architecture/patterns/sharding Orders sharded by city.
• Cache-Aside — Azure Cloud Design Patterns. https://learn.microsoft.com/azure/architecture/patterns/cache-aside Load-on-miss for the menu; pair with an invalidation strategy.
• Soft Delete / Temporal — Fowler, temporal patterns (https://martinfowler.com/eaaDev/timeNarrative.html); SQL:2011 system-versioned temporal tables (https://learn.microsoft.com/sql/relational-databases/tables/temporal-tables). Menu-price history you can recover and audit.
• Honorable mentions — lightweight Unit of Work (Fowler, PoEAA, https://martinfowler.com/eaaCatalog/unitOfWork.html — used here only as a transaction boundary, not an ORM); Read Replicas; Connection Pooling.