patterns-reference

Architecture Patterns Reference

Quick reference for common patterns with usage guidance.

Data Access Patterns

Pattern	When to Use	When NOT to Use	Complexity
Active Record	Simple CRUD, rapid prototyping	Complex queries, multiple sources	Low
Repository	Testing needed, multiple sources	Simple CRUD, single database	Medium
Unit of Work	Complex transactions	Simple operations	High
Data Mapper	Complex domain, performance	Simple CRUD, rapid dev	High

Domain Logic Patterns

Pattern	When to Use	When NOT to Use	Complexity
Transaction Script	Simple CRUD, procedural	Complex business rules	Low
Table Module	Record-based logic	Rich behavior needed	Low
Domain Model	Complex business logic	Simple CRUD	Medium
DDD (Full)	Complex domain, domain experts	Simple domain, no experts	High

Distributed System Patterns

Pattern	When to Use	When NOT to Use	Complexity
Modular Monolith	Small teams, unclear boundaries	Clear contexts, different scales	Medium
Microservices	Different scales, large teams	Small teams, simple domain	Very High
Event-Driven	Real-time, loose coupling	Simple workflows, strong consistency	High
CQRS	Read/write performance diverges	Simple CRUD, same model	High
Saga	Distributed transactions	Single database, simple ACID	High

API Patterns

Pattern	When to Use	When NOT to Use	Complexity
REST	Standard CRUD, resources	Real-time, complex queries	Low
GraphQL	Flexible queries, multiple clients	Simple CRUD, caching needs	Medium
gRPC	Internal services, performance	Public APIs, browser clients	Medium
WebSocket	Real-time updates	Simple request/response	Medium

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Simplicity Principle

“Start simple, add complexity only when proven necessary.”

• You can always add patterns later
• Removing complexity is MUCH harder than adding it
• When in doubt, choose simpler option