implementing-ddd-architecture

name	implementing-ddd-architecture
description	Design and implement DDD patterns (entities, value objects, aggregates, CQRS). Use when creating new domain objects, implementing bounded contexts, designing repository interfaces, or learning proper layer separation. For fixing existing Deptrac violations, use the deptrac-fixer skill instead.

Implementing DDD Architecture

Context (Input)

• Creating new entities, value objects, or aggregates
• Implementing bounded contexts or modules
• Designing repository interfaces and implementations
• Learning proper layer separation (Domain/Application/Infrastructure)
• Need to understand CQRS pattern (Commands, Handlers, Events)
• Code review for architectural compliance

Task (Function)

Design and implement rich domain models following DDD, hexagonal architecture, and CQRS patterns.

Success Criteria:

• Domain entities remain framework-agnostic (no framework imports)
• Business logic in Domain layer, not in Application handlers
• make deptrac shows zero violations
• Repository interfaces in Domain, implementations in Infrastructure

---

Core Principle

Rich Domain Models, Not Anemic

Business logic belongs in the Domain layer. Application layer orchestrates, Domain executes.

---

Architecture Planning: Existing Structure First

When writing architecture specs or proposing new classes for this repository, inspect the current source tree and deptrac.yaml before inventing directories.

Required workflow:

1. List existing directories for the bounded context, for example find src/Core/Customer -maxdepth 4 -type d | sort.
2. Check deptrac.yaml collectors for allowed Application, Domain, and Infrastructure directory names.
3. Reuse existing type directories whenever they already express the class responsibility.
4. Keep the rule one directory = one class type. Do not place policies, schedulers, registries, handlers, DTOs, and resolvers together in a broad feature bucket.
5. If a feature already exists through Repository, Collection, Resolver, EventSubscriber, or other established directories, extend that feature surface instead of creating a new umbrella directory such as Cache.
6. Introduce a new directory type only when no existing type fits, it is added to deptrac, and the architecture spec explains why the new type is necessary.

For CQRS in this codebase, prefer:

• Application/Command/{Action}{Entity}Command.php
• Application/CommandHandler/{Action}{Entity}CommandHandler.php

Do not propose ReadModel, Query, QueryHandler, Message, MessageHandler, Policy, Registry, or Scheduler directories unless the current repo already uses that directory type and deptrac collects it. Reads in the current Customer context are served by repositories, resolvers, processors, and DTOs rather than a separate read-model directory.

Example for Customer cache planning:

• Shared reusable refresh work: Shared/Application/Command/CacheRefreshCommand.php
• Shared reusable worker: Shared/Application/CommandHandler/CacheRefreshCommandHandler.php
• Shared reusable handler base: Shared/Application/CommandHandler/AbstractCacheRefreshCommandHandler.php
• Shared reusable metrics: Shared/Application/Observability/Metric/CacheRefreshSucceededMetric.php
• Customer adapter execution: Core/Customer/Application/CommandHandler/CustomerCacheRefreshCommandHandler.php
• Customer adapter factory: Core/Customer/Application/Factory/CustomerCacheRefreshCommandFactory.php
• Customer policy lookup: Core/Customer/Infrastructure/Collection/CustomerCachePolicyCollection.php plus Core/Customer/Infrastructure/Resolver/CustomerCachePolicyResolver.php
• Customer cached storage access: existing Core/Customer/Infrastructure/Repository/CachedCustomerRepository.php

When a feature must be reusable across bounded contexts, put the generic command, worker, abstract base classes, DTOs, resolver interfaces, and metrics in Shared first. Keep each bounded context as a thin adapter that maps its domain events, tags, targets, policies, and repository warmup behavior into the shared contract. Do not route Customer-specific command payloads if the same queue and worker must later refresh other domains.

---

Layer Dependency Rules

Domain ─────────────────> (NO dependencies - pure PHP)
           │
           │
Application ──────────> Domain + Infrastructure
           │
           │
Infrastructure ───────> Domain + Application

Allowed Dependencies:

Layer	Can Import
Domain	❌ Nothing (pure PHP, SPL, domain-specific libraries only)
Application	✅ Domain, Infrastructure, Symfony, API Platform
Infrastructure	✅ Domain, Application, Symfony, Doctrine, MongoDB

See: DIRECTORY-STRUCTURE.md for complete file placement guide.

---

Critical Rules

0. No Static Methods in Production Source

Do not add or keep static method declarations in project PHP files. Model behavior as injected services, listeners, factories, or regular value objects so dependencies remain explicit and testable.

• HTTP request preconditions belong in kernel listeners, not static guards inside processors
• Object creation belongs in factory services
• Shared helpers should be injectable services
• Run make forbid-static-methods or make psalm before finishing

1. Domain Layer Purity

❌ FORBIDDEN in Domain:

• Symfony components (use Symfony\...)
• Doctrine annotations/attributes
• API Platform attributes
• Any framework-specific code

✅ ALLOWED in Domain:

• Pure PHP
• SPL (Standard PHP Library)
• Domain-specific value objects
• Domain interfaces

2. Rich Domain Models

❌ BAD (Anemic):

class Customer {
    public function setName(string $name): void {
        $this->name = $name;  // No validation!
    }
}

✅ GOOD (Rich):

class Customer {
    public function changeName(CustomerName $name): void {
        // Business rules enforced
        $this->record(new CustomerNameChanged($this->id, $name));
        $this->name = $name;
    }
}

3. Validation Pattern

❌ BAD: Validation in Domain with Symfony

use Symfony\Component\Validator\Constraints as Assert;

class Customer {
    #[Assert\NotBlank]  // ❌ Framework in Domain!
    private string $name;
}

✅ GOOD: Validation in YAML config (Preferred)

# config/validator/Customer.yaml
App\Application\DTO\CustomerCreate:
  properties:
    name:
      - NotBlank: ~
      - Length:
          min: 2
          max: 100

Framework validators should always be used when possible. They provide:

• Centralized configuration
• Easy maintenance
• Standard error messages
• Built-in constraints (NotBlank, Email, Length, etc.)
• Custom validators for business rules

Value Objects should only be used when:

• Framework validators cannot express the business rule
• Complex domain logic requires encapsulation
• The validation is part of domain invariants

See: REFERENCE.md for complete validation patterns.

---

CQRS Pattern Quick Start

Commands (Write Operations)

// src/Core/{Context}/Application/Command/{Action}{Entity}Command.php
final readonly class CreateCustomerCommand implements CommandInterface
{
    public function __construct(
        public string $id,
        public string $name,
        public string $email
    ) {}
}

Command Handlers

// src/Core/{Context}/Application/CommandHandler/{Action}{Entity}CommandHandler.php
final readonly class CreateCustomerCommandHandler implements CommandHandlerInterface
{
    public function __invoke(CreateCustomerCommand $command): Customer
    {
        // Minimal orchestration only
        $customer = Customer::create(
            Ulid::fromString($command->id),
            new CustomerName($command->name),
            new Email($command->email)
        );

        $this->repository->save($customer);
        $this->eventBus->publish(...$customer->pullDomainEvents());

        return $customer;
    }
}

See: REFERENCE.md for complete CQRS patterns.

---

Repository Pattern

Interface (Domain Layer)

// src/Core/{Context}/Domain/Repository/{Entity}RepositoryInterface.php
interface CustomerRepositoryInterface
{
    public function save(Customer $customer): void;
    public function findById(string $id): ?Customer;
}

Implementation (Infrastructure Layer)

// src/Core/{Context}/Infrastructure/Repository/{Entity}Repository.php
final class CustomerRepository implements CustomerRepositoryInterface
{
    public function __construct(
        private readonly DocumentManager $documentManager
    ) {}

    public function save(Customer $customer): void
    {
        $this->documentManager->persist($customer);
        $this->documentManager->flush();
    }
}

Register in config/services.yaml:

App\Core\Customer\Domain\Repository\CustomerRepositoryInterface:
  alias: App\Core\Customer\Infrastructure\Repository\CustomerRepository

---

Domain Events Pattern

Recording Events in Aggregates

class Customer extends AggregateRoot  // Provides event recording
{
    public function changeName(CustomerName $name): void
    {
        $this->name = $name;
        $this->record(new CustomerNameChanged($this->id, $name));
    }
}

Event Subscribers

// src/Core/{Context}/Application/EventSubscriber/{Event}Subscriber.php
final readonly class CustomerNameChangedSubscriber implements DomainEventSubscriberInterface
{
    public function __invoke(CustomerNameChanged $event): void
    {
        // React to event (e.g., send notification)
    }
}

See: REFERENCE.md for complete event-driven patterns.

---

Quick Start Workflows

Creating a New Entity

1. Create Entity in Domain/Entity/
2. Create Value Objects in Domain/ValueObject/
3. Create Repository Interface in Domain/Repository/
4. Create Repository Implementation in Infrastructure/Repository/
5. Create Commands in Application/Command/
6. Create Handlers in Application/CommandHandler/
7. Verify: make deptrac shows zero violations

See: examples/ for complete working examples.

Fixing Deptrac Violations

If make deptrac shows violations:

Use: deptrac-fixer skill for step-by-step fix patterns.

---

Constraints

NEVER

• Add framework imports to Domain layer
• Put business logic in Application handlers
• Create anemic domain models (getters/setters only)
• Modify deptrac.yaml to allow violations
• Skip validation (either in Value Objects or YAML config)
• Use public setters in entities
• Create a new feature bucket directory when existing class-type directories fit
• Propose directories that deptrac does not collect without explicitly updating and validating deptrac

ALWAYS

• Keep Domain layer pure (no framework dependencies)
• Put business logic in Domain entities/aggregates
• Use Value Objects for validation and invariants
• Create repository interfaces in Domain layer
• Implement repositories in Infrastructure layer
• Use Command Bus for write operations
• Record Domain Events for state changes
• Reuse existing bounded-context directory names before adding new ones
• Keep one directory focused on one class type
• Verify with make deptrac after changes

---

Format (Output)

Expected Directory Structure

src/Core/{Context}/
├── Domain/
│   ├── Entity/
│   │   └── {Entity}.php          # Pure PHP, no attributes
│   ├── ValueObject/
│   │   └── {ValueObject}.php     # Validation logic here
│   ├── Repository/
│   │   └── {Entity}RepositoryInterface.php
│   ├── Event/
│   │   └── {Event}.php
│   └── Exception/
│       └── {Exception}.php
├── Application/
│   ├── Command/
│   │   └── {Action}{Entity}Command.php
│   ├── CommandHandler/
│   │   └── {Action}{Entity}CommandHandler.php
│   └── EventSubscriber/
│       └── {Event}Subscriber.php
└── Infrastructure/
    └── Repository/
        └── {Entity}Repository.php

Expected Deptrac Output

✅ No violations found

---

Verification Checklist

After implementing DDD patterns:

• Domain entities have no framework imports
• Business logic in Domain layer, not Application
• Value Objects used for validation and invariants
• Repository interfaces in Domain layer
• Repository implementations in Infrastructure layer
• Commands implement CommandInterface
• Handlers implement CommandHandlerInterface
• Domain Events recorded in aggregates
• Event Subscribers implement DomainEventSubscriberInterface
• make deptrac shows zero violations
• All tests pass
• make ci passes

---

Related Skills

• deptrac-fixer - Fix architectural violations
• api-platform-crud - YAML-based API Platform with DDD
• database-migrations - XML-based Doctrine mappings
• complexity-management - Keep domain logic maintainable

---

Reference Documentation

For detailed patterns, workflows, and examples:

• REFERENCE.md - Complete DDD workflows and patterns
• DIRECTORY-STRUCTURE.md - File placement guide (CodelyTV style)
• examples/ - Complete working examples:
  • Entity examples
  • Value Object examples
  • CQRS examples
  • Event-driven examples

---

Anti-Patterns to Avoid

❌ Business Logic in Handlers

// ❌ BAD: Logic in handler
class CreateCustomerHandler {
    public function __invoke($command) {
        if (strlen($command->name) < 2) {  // ❌ Validation in handler!
            throw new Exception();
        }
        // ...
    }
}

❌ Framework Dependencies in Domain

// ❌ BAD: Symfony in Domain
use Symfony\Component\Validator\Constraints as Assert;

class Customer {
    #[Assert\NotBlank]  // ❌ Framework coupling!
    private string $name;
}

❌ Anemic Domain Models

// ❌ BAD: Just getters/setters
class Customer {
    public function setName(string $name): void {
        $this->name = $name;  // No business rules!
    }
}

✅ GOOD Patterns

• Value Objects enforce invariants
• Domain methods express business operations
• Handlers orchestrate, Domain executes
• Configuration externalized to YAML/XML

---

CodelyTV Architecture Pattern

This project follows CodelyTV's hexagonal architecture patterns:

• Directory structure: Bounded Context → Layer → Component Type
• Naming conventions: Explicit suffixes (Command, Handler, Repository, etc.)
• Layer isolation: Deptrac enforces boundaries
• CQRS: Commands for writes, Queries for reads
• Event-driven: Domain Events for decoupling

See: DIRECTORY-STRUCTURE.md for complete hierarchy.