Domain Driven Design

Apply these patterns when implementing domain logic in TypeScript/Deno.

Building Block Selection

Choose the appropriate type based on these criteria:

Type	Identity	Mutability	When to Use
Value Object	None (equality by value)	Immutable	Measurements, descriptions, identifiers, money, dates, addresses
Entity	Has unique ID	Mutable	Things with lifecycle, tracked over time, referenced by ID
Aggregate	Root entity + children	Root controls mutations	Consistency boundary, transactional unit, enforce invariants
Domain Service	None	Stateless	Operations spanning multiple aggregates, external integrations
Repository	None	Stateless	Persistence abstraction for aggregates only
Application Service	None	Stateless	Orchestrate domain objects for a use case; own the transaction boundary; return results or emit progress events; live in the application/libswamp layer, not the domain