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DDD

In this pattern, you use only the tactical elements that are part of core DDD.

Elements

Element Layer Purpose
Application Service Application Orchestrates business operations by coordinating between the domain logic and infrastructure components.
Aggregates Domain A cluster of domain entities that are treated as a single unit, ensuring consistency and encapsulating business logic.
Events Domain A record of a significant change in state or behavior within the domain, which can trigger subsequent processing.
Event Handlers Domain A component that listens for specific events and executes business logic in response to those events.
Repository Application A data access layer that provides an abstraction for retrieving and persisting domain objects, ensuring that domain logic remains isolated from data storage concerns.
Persistence Store Infrastructure A general-purpose storage system that holds the application's data, typically used for saving the current state of domain objects outside of event-driven contexts.
Event Store Infrastructure A specialized storage system that captures and persists all domain events, allowing the reconstruction of aggregate states and enabling event sourcing patterns.

Workflow

Pure DDD

  1. Request: Application receives a client request at the API layer
  2. DTO (Data Transfer Object): The API converts the request data into a DTO, encapsulating the necessary information to pass to the Application Service, and invokes a specific use case.
  3. Application Service: Application Service asks for the aggregate instance from the Repository.
  4. Repository: The repository hydrates an aggregate from the Persistence Store.
  5. Aggregate: The Application Service invokes the correct behavior on the Aggregate along with request data.
  6. Output: The Aggregate processes the data, and if successful, an event is generated as a result of a state change or a business operation.
  7. Repository: The Application Service persists the processed data and events via the Repository again.
  8. Persistence: The Repository saves the updated data back into the Persistence Store.
  9. Event Store: Any events generated by the Aggregate are stored in the Event Store by the repository.