Domain Layer

The Domain Layer contains the core business logic. It is completely independent of infrastructure concerns.

In This Section

• Entities - Objects with identity and lifecycle
• Aggregates - Consistency boundaries and cross-aggregate patterns
• Value Objects - Immutable, self-validating primitives
• Identifiers - Typed unique identifiers for entities
• Enums - Finite value sets with domain behavior
• Specifications - Composable business rules for querying
• Domain Events - Facts that happened in the domain
• Domain Exceptions - Business rule violation errors
• Repository Interfaces - Persistence abstractions (ports)
• Collections - Typed collections for domain objects
• DateTime Formats - Standard date/time format constants

Key Principles

Independence: The Domain Layer has no dependencies on other layers. It defines interfaces (ports) that infrastructure implements.

Immutability: Value Objects are readonly classes and return new instances on state changes. Entities use readonly on identity properties; state properties mutate in place via behavior methods.

Self-Validation: Value Objects validate their data in constructors. Invalid data cannot exist.

Ubiquitous Language: Class and method names reflect business terminology.