Designing a Domain Model That Actually Models the Domain

Based on your detailed explanation of moving from a procedural approach to a domain-driven design (DDD) approach in Python, it seems you're aiming for a more robust architecture that encapsulates business logic within domain objects. Let's break down the key points and discuss how to proceed with wiring everything together.

Key Points Recap

1. Domain Objects:

   • Encapsulate behavior (OrderItem.subtotal(), Order.total(), etc.)
   • Handle validation in __post_init__
   • Implement state machines (e.g., Order.place() and Order.cancel())

2. Value Objects:

   • Immutable
   • Self-validating

3. Services:

   • Coordinate domain objects but don't compute business logic themselves.

Next Steps: Wiring It All Together

To wire everything together, you'll need to introduce the application layer that connects your domain models with external systems (e.g., databases, APIs). This involves:

1. Ports and Adapters Architecture:

   • Define interfaces for repositories (ports).
   • Implement concrete repository classes (adapters) that interact with the database.

2. Dependency Injection:

   • Use a dependency injection framework to manage object

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