ddd-patterns

name	ddd-patterns
description	DDD Patterns: Domain logic, aggregates, value objects, bounded contexts, domain events.
triggers	{"keywords":["domain","aggregate","entity","value object","repository","bounded context","domain event","ubiquitous language"]}
auto_load_when	Designing domain models or business logic
agent	architect
tools	["Read","Write","Bash"]

Domain-Driven Design Patterns

Focus: Ubiquitous language, bounded contexts, domain modeling

1. Building Blocks

DDD Tactical Patterns:
├── Entities - identity, mutable
├── Value Objects - immutable, no identity
├── Aggregates - consistency boundary
├── Domain Services - stateless logic
├── Domain Events - something happened
├── Repositories - collection-like access
└── Factories - complex creation

---

2. Entity vs Value Object

Entity:
├── Has unique ID
├── Mutable state
├── Equality by ID
└── Example: User, Order, Product

Value Object:
├── No ID
├── Immutable
├── Equality by attributes
└── Example: Address, Money, Color

---

3. Aggregate Pattern

Aggregate Root:
├── Entry point for access
├── Enforces invariants
├── Controls changes
└── Example: Order (contains OrderItems)

Aggregate Rules:
├── One root per aggregate
├── Only root accessible from outside
├── Changes via root only
├── Consistency boundary
└── Transaction scope = aggregate

---

4. Bounded Context

What is a BC:
├── Explicit boundary
├── Own domain model
├── Own ubiquitous language
└── Own team ownership

How to identify:
├── Different domain vocabularies
├── Different team responsibilities
├── Different scaling needs
└── Different DB schemas

---

5. Domain Events

Event structure:
├── Unique ID
├── Occurred at timestamp
├── Event type name
├── Payload (what happened)

When to use:
├── Decouple components
├── Audit trail
├── CQRS read models
└── Event sourcing

---

6. When to Apply DDD

Apply DDD when:
├── Complex business domain
├── Ubiquitous language exists
├── Domain experts available
├── Long-term investment
└── Team understands patterns

Avoid when:
├── CRUD-heavy app
├── Simple domain
├── No domain expert
└── Tight timeline

---

7. Repository Pattern

Repository:
├── Collection metaphor
├── Methods: add, remove, getById
├── Query methods (find)
└── Implementation: DB or API

Interface in domain
Implementation in infrastructure

---

8. Service Layer vs Domain Service

Application Service:
├── Orchestrates use cases
├── Transaction management
├── Coordinates entities
└── Thin, declarative

Domain Service:
├── Pure business logic
├── Stateless
├── Between entities
└── When logic doesn't fit entity

---

Key Patterns

1. Aggregate - transactional boundary
2. Value Object - immutable descriptors
3. Bounded Context - model boundary
4. Ubiquitous Language - shared vocabulary
5. Domain Events - decoupled communication

(End of file - 90 lines)

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Anti-Patterns

❌ Anemic domain model (entities are just data structs)
✅ Rich entities with behavior — User.changeEmail(), Order.place()

❌ Aggregate that spans too many entities
✅ Keep aggregates small; one transaction = one aggregate

❌ Domain events published synchronously blocking the caller
✅ Collect events in aggregate; dispatch after transaction commits

❌ Business logic in application services or controllers
✅ Logic belongs to entities and domain services

❌ Exposing aggregate internals to the outside
✅ Only aggregate root is accessible from outside; internal objects are private

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Quick Reference

Concept	Role	Rule
Entity	Identity + lifecycle	Mutable; identified by ID
Value Object	Describe by value	Immutable; no identity
Aggregate	Consistency boundary	One transaction per aggregate
Domain Event	Side effect trigger	Immutable; past tense name
Repository	Persistence facade	Returns full aggregates
Domain Service	Stateless logic	When logic doesn't fit entity
Bounded Context	Linguistic boundary	Each team owns its context

🌍 Universal Language Support

• Turkish Native: This skill natively supports Turkish. If the user prompt is in Turkish, all analysis, formatting, and output MUST be entirely in Turkish. You do not need explicit "write in Turkish" instructions.