Individual skill
ddd
Domain-Driven Design tactical patterns for .NET applications. Covers aggregates, aggregate roots, value objects, domain events, domain services, strongly-typed IDs, and repository patterns for aggregate persistence. Load this skill when implementing DDD, working with aggregates, value objects, domain events, bounded contexts, or when the architecture-advisor recommends DDD + Clean Architecture. Pair with the clean-architecture skill.
skills/ddd/SKILL.md
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# Domain-Driven Design (DDD)
## Core Principles
1. **Aggregates define consistency boundaries** — An aggregate is a cluster of entities and value objects treated as a single unit for data changes. All invariants within an aggregate are enforced in a single transaction. Cross-aggregate consistency is eventual.
2. **Value objects over primitives** — Replace primitive obsession with value objects. `Money`, `EmailAddress`, `OrderNumber` are not strings — they carry validation, equality, and behavior. Use C# records for immutable value objects.
3. **Domain events decouple side effects** — When something meaningful happens in the domain (OrderPlaced, PaymentReceived), raise a domain event. Side effects (send email, update read model, notify another aggregate) subscribe to these events. The aggregate stays focused on its own rules.
4. **Aggregate root is the sole entry point** — External code accesses an aggregate only through its root entity. Child entities are never loaded or modified independently. The root enforces all invariants for the entire aggregate.
5. **Repositories persist aggregates, not entities** — One repository per aggregate root. The repository loads and saves the entire aggregate as a unit. No repository for child entities. The Infrastructure implementation uses `DbContext` internally — this is a DDD tactical pattern for aggregate boundaries, not a generic CRUD wrapper.
## Patterns
### Aggregate Root
