Design Patterns¶

This section describes the key design patterns used throughout ascetic-ddd.

Domain Patterns¶

Aggregate¶

The Aggregate pattern enforces consistency boundaries. Each aggregate has a root entity that controls access to its internal objects.

Repository¶

The Repository pattern provides collection-like access to aggregates. Implementations exist for PostgreSQL (psycopg-based).

Specification¶

The Specification pattern encapsulates query criteria. Supported flavors:

• JSONPath: RFC 9535 and jsonpath2 implementations

• Lambda filter: In-memory predicate-based filtering

• Query lookup: MongoDB-like query operators ($eq, $gt, $in, $rel, etc.)

Infrastructure Patterns¶

Transactional Outbox¶

The Outbox pattern ensures reliable event publishing by writing events to a database table within the same transaction as the business operation.

Idempotent Inbox¶

The Inbox pattern ensures messages are processed exactly once using deduplication based on message identifiers.

Saga¶

The Saga pattern coordinates distributed transactions across multiple aggregates or services using compensating actions.

Unit of Work¶

Session management implements the Unit of Work pattern, tracking changes and committing them atomically.

Test Data Patterns¶

Provider Topology¶

The faker module uses a Provider topology where each provider is responsible for generating a specific piece of test data. Providers form a directed acyclic graph with reference providers linking aggregates.

Distribution Strategies¶

Distributor strategies control how test data is selected or created:

• Sequence: Round-robin through existing data

• Weighted: Probability-weighted selection

• Random: Random selection from available pool