DDD Entity Generator

DDD Entity Generator

Generate domain layer components including entities, value objects, repository interfaces, domain events, and errors following Domain-Driven Design principles.

What This Skill Does

Creates pure business logic components for the domain layer with zero framework dependencies:

• Entities: Business objects with identity, factory methods, and encapsulation
• Value Objects: Immutable, validated value types (Email, Money, PhoneNumber, etc.)
• Repository Interfaces: Data persistence contracts returning domain entities
• Domain Events: Immutable event classes for state changes
• Domain Errors: Business-specific error types with error codes

When to Use This Skill

Use when you need to:

• Add new entities to an existing context
• Create value objects for validation and type safety
• Define repository interfaces for data access
• Add domain events for event-driven architecture
• Create domain-specific errors

Examples:

• "Create a Product entity with Price and SKU value objects"
• "Generate a Customer entity with Email and PhoneNumber"
• "Add an Order entity with OrderLine value objects"

Key Patterns

Entity Pattern

export class EntityName {
  private constructor(
    private readonly id: string,
    private name: string,
    private readonly createdAt: Date,
    private updatedAt: Date
  ) {}

  static create(data: CreateData): EntityName {
    const id = randomUUID();
    const now = new Date();
    const entity = new EntityName(id, data.name, now, now);
    entity.validate();
    return entity;
  }

  static reconstitute(data: PersistedData): EntityName {
    return new EntityName(
      data.id,
      data.name,
      data.createdAt,
      data.updatedAt
    );
  }

  getId(): string { return this.id; }
  getName(): string { return this.name; }

  changeName(newName: string): void {
    this.name = newName;
    this.updatedAt = new Date();
  }

  private validate(): void {
    if (!this.name) throw new InvalidDataError('Name required');
  }
}

Value Object Pattern

export class Email {
  private readonly value: string;

  private constructor(value: string) {
    this.value = value;
  }

  static create(value: string): Email {
    const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
    if (!emailRegex.test(value)) {
      throw new InvalidEmailError(value);
    }
    return new Email(value.toLowerCase());
  }

  getValue(): string {
    return this.value;
  }

  equals(other: Email): boolean {
    return this.value === other.value;
  }
}

Repository Interface Pattern

export interface IEntityRepository {
  save(entity: EntityName): Promise<void>;
  findById(id: string): Promise<EntityName | null>;
  findByEmail(email: Email): Promise<EntityName | null>;
  findAll(limit?: number, offset?: number): Promise<EntityName[]>;
  delete(id: string): Promise<void>;
  exists(id: string): Promise<boolean>;
}

Domain Event Pattern

export class EntityCreated {
  constructor(
    public readonly entityId: string,
    public readonly name: string,
    public readonly timestamp: Date = new Date()
  ) {}
}

Domain Error Pattern

export class DomainError extends Error {
  constructor(
    message: string,
    public readonly code: string
  ) {
    super(message);
    this.name = this.constructor.name;
  }
}

export class EntityNotFoundError extends DomainError {
  constructor(id: string) {
    super(`Entity with ID '${id}' not found`, 'ENTITY_NOT_FOUND');
  }
}

Critical Rules

MUST DO:

• Private constructor for entities
• Static create() and reconstitute() methods
• Getters for all properties (no public properties)
• Value objects must be immutable (readonly)
• Validation in static factory methods
• Zero framework dependencies
• No database annotations
• Repository interfaces (not implementations)

MUST NOT:

• Import framework code (Mongoose, Elysia, etc.)
• Use any types
• Make constructors public
• Use mutable value objects
• Add database annotations to entities
• Implement repositories in domain layer

Generated Files

/​src/​contexts/​{Context}/​domain/
├── entities/
│   └── {entity}.entity.ts
├── value-objects/
│   ├── email.vo.ts
│   ├── phone-number.vo.ts
│   └── {custom}.vo.ts
├── repositories/
│   └── {entity}.repository.interface.ts
├── events/
│   ├── {entity}-created.event.ts
│   ├── {entity}-updated.event.ts
│   └── {entity}-deleted.event.ts
├── errors/
│   └── {context}.errors.ts
└── index.ts

Common Value Objects

The skill can generate these common value objects:

• Email: Email validation with lowercase normalization
• PhoneNumber: Phone number validation
• Money: Amount + currency with arithmetic operations
• Address: Street, city, state, zip validation
• DateRange: Start/​end date validation
• URL: URL validation
• UUID: UUID validation

Validation Checklist

After generation, verify:

• Entities have private constructor
• Static create() and reconstitute() methods present
• All properties accessed via getters
• Value objects are immutable (readonly)
• Validation logic in factory methods
• No framework imports
• No database annotations
• Repository interfaces defined (not implementations)
• Domain events immutable
• Error codes included in domain errors

Integration

Update the domain barrel export (domain/​index.ts):

export * from './​entities/​{entity}.entity';
export * from './​value-objects/​{vo}.vo';
export * from './​repositories/​{entity}.repository.interface';
export * from './​errors/​{context}.errors';
export * from './​events/​{entity}.events';

Related Skills

• ddd-context-generator: Generate complete bounded context
• ddd-usecase-generator: Generate use cases using these entities
• ddd-validator: Validate domain layer compliance