Domain-Driven Design (DDD): Advanced Patterns

Advanced integration patterns for handling complex distributed system interactions and transactional consistency.

🚀 Advanced Patterns

1. CQRS (Command Query Responsibility Segregation): Separation of write (Command) and read (Query) models to optimize performance and scalability.
2. Event Sourcing: Capturing all changes to the state of an application as a sequence of events (The current state is reconstructed from the log).
3. Outbox Pattern: Ensuring transactional consistency between a database and a message broker. (Save to DB and a 'Message Outbox' in the same transaction).
4. ACL (Anti-Corruption Layer): Translating and isolating external systems' models to maintain the integrity of your core domain model.

⚡ CQRS + Event Sourcing Workflow

1. Command Side: Receives request -> Aggregate Root (AR) validates -> AR emits Event -> Event saved to Event Store.
2. Projection Side: Projector listens to Events -> Updates Read Model (Optimized for queries: e.g., Elasticsearch, Read DB).
3. Query Side: Reads from Read Model only.

🚫 Advanced Anti-Patterns

• Premature CQRS: Adding CQRS to simple systems. (Increases complexity needlessly).
• The Giant Event: Capturing too much state in a single event. (Events should be granular business facts).
• Ignoring Eventual Consistency: Forgetting that Read Models may be out of sync for a short time. Solution: Compensating actions or UI feedback.

🔗 Integration Checklist

• Is the Outbox pattern used for cross-container communication?
• Is the ACL properly shielding the Core Domain?
• Are events immutable and versioned?