Service Layer Patterns

Sources: Martin Fowler — PoEAA (2002); Eric Evans — Domain-Driven Design (2003)

Pain Signals — You Are in This Branch When:

• Business rules (if order.total > 1000: apply_discount()) live inside service classes
• Controllers or API handlers contain domain logic
• Domain objects are anemic — they hold data but all behaviour is in services
• A service method does both "figure out what to do" and "do it"
• The same business rule appears in multiple service methods and drifts over time
• It is unclear whether a piece of logic belongs in a service or a domain object

Pattern Selection