Domain layer

Architectural Patterns

Meaning

The domain layer encapsulates the core business logic and domain model, including entities, value objects, services, and repositories, isolated from infrastructure concerns.

Primary Function

Encapsulates enterprise business rules and defines the domain model.

Communicative Purpose

Refers to the layer where business logic resides when discussing layered architecture or domain-driven design.

Pattern

Define entities, value objects, and domain services; expose repository interfaces for persistence

Core Structure

Consists of entities, value objects, domain services, and repository interfaces that express the business model.

Função primária

Encapsulates enterprise business rules and defines the domain model.

Propósito comunicativo

Refers to the layer where business logic resides when discussing layered architecture or domain-driven design.

Situações de gatilho

When discussing layered architecture, separating concerns, or explaining where business rules belong.

Contextos

Software architecture discussions, domain-driven design tutorials, code reviews, architectural diagrams.

Padrão

Define entities, value objects, and domain services; expose repository interfaces for persistence

Estrutura central

Consists of entities, value objects, domain services, and repository interfaces that express the business model.

Colocados típicos

entity
repository
service
aggregate
value object

Substituições comuns

Combine domain and application layers in small projects → reduces architectural overhead but may blur boundaries
Use a service layer instead of domain services → simplifies domain model but can lead to anemic domain

Erros comuns

Confusing domain layer with application or infrastructure layers; placing infrastructure concerns inside the domain layer.

Similar / contraste

application layer, infrastructure layer, presentation layer

Interferências

Coming from procedural C: treating the domain layer as a simple data struct collection → loses encapsulation of business rules; Coming from MVC frameworks: placing persistence code in the domain layer → violates clean architecture boundaries

Família do chunk

Domain-Driven Design layers

Nuance

Refers specifically to the core business logic, excluding persistence, UI, or external service concerns.

Efeito pragmático

Signals adherence to domain-driven design principles and clean architecture boundaries.

Dica de memória

Think of the domain layer as the heart of the system, pumping core business rules through the veins of the application.

Nota

The domain layer must depend only on abstractions; concrete infrastructure implementations should be injected via interfaces.

Upgrade path

Application layer

Frequência: HighFormulaicidade: FlexibleTipo de construção: Layered architecture component representing business rulesPrioridade de aquisição: Automatic productionPrioridade de output: InputTag de espaçamento: Medium-term

Examples

public class Order { private OrderId id; private Customer customer; private List<OrderLine> lines; public Order(OrderId id, Customer customer) { this.id = id; this.customer = customer; this.lines = new ArrayList<>(); } public void addLine(OrderLine line) { lines.add(line); } public Money totalPrice() { return lines.stream().map(OrderLine::getPrice).reduce(Money.ZERO, Money::add); } }

public interface OrderRepository { Order findById(OrderId id); List<Order> findByCustomer(CustomerId customerId); void save(Order order); void delete(OrderId id); }

public class OrderPlacementService { private final OrderRepository repository; private final NotificationService notificationService; public OrderPlacementService(OrderRepository repository, NotificationService notificationService) { this.repository = repository; this.notificationService = notificationService; } public void placeOrder(Order order) { // business logic: validate, calculate totals, persist repository.save(order); notificationService.sendOrderConfirmation(order); } }