ddd

name	ddd
description	Domain-Driven Design, bounded contexts, aggregates, and domain modeling
license	MIT
compatibility	opencode
metadata	{"audience":"developers","category":"software-development"}

What I do

• Design bounded contexts and their boundaries
• Create rich domain models
• Implement aggregates and aggregate roots
• Design value objects
• Define domain events
• Apply strategic and tactical DDD

When to use me

When building complex domain logic, modeling business domains, or structuring large applications.

Strategic Design

Bounded Contexts

• Clear boundaries around domain models
• Each context has its own ubiquitous language
• Context mapping relationships:
  • Customer/Supplier: Upstream/downstream
  • Conformist: Downstream follows upstream
  • Anticorruption Layer: Translation layer
  • Open Host Service: Published language
  • Separate Ways: No relationship

Ubiquitous Language

• Shared language between developers and domain experts
• Embedded in code (class names, methods)
• Consistent terminology

Context Maps

• Visual representation of system boundaries
• Integration points
• Team responsibilities

Tactical Design

Entities

• Identity that persists over time
• Mutable state
• Unique identifier

class Order {
    private OrderId id;
    private Money total;
    // Entity with unique ID
}

Value Objects

• Immutable
• No identity
• Compares by value

class Money {
    private final BigDecimal amount;
    private final Currency currency;
    // Value object - immutable, compared by value
}

Aggregates

• Cluster of related objects
• Aggregate root controls access
• Invariants enforced within boundary
• One entity per aggregate typically

class OrderAggregate {
    private OrderId id;
    private List<OrderLine> lines; // Only aggregate root can modify
    
    public void addLine(Product product, int quantity) {
        // Invariants enforced here
    }
}

Domain Events

• Something significant happened
• Immutable
• Named in past tense

class OrderPlacedEvent {
    private OrderId orderId;
    private Money total;
    private Instant occurredAt;
}

Repositories

• Collection-like interface
• Persist aggregates
• Abstract storage details

Domain Services

• Operations that don't belong to entities
• Cross-aggregate operations
• Stateless

Factories

• Complex object creation
• Hide implementation details

DDD Patterns

• CQRS with DDD
• Event sourcing
• Specification pattern
• Side effects
• Policy
• Strategy