Domain Driven

Domain-Driven Design Skill — Complete Business Module Builder

This skill ensures every business module is built completely with all sub-modules, CRUD operations, relationships, and business rules — NO mockups, NO placeholders.

Module Discovery Protocol

When asked to build an business module:

Step 1: Enumerate Sub-Modules

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For module "Inventory", identify:
├── Products (CRUD + categories, variants, pricing)
├── Warehouses (CRUD + locations, capacity)
├── Stock Movements (CRUD + types: in, out, transfer)
├── Suppliers (CRUD + contacts, contracts)
├── Purchase Orders (CRUD + lines, receiving)
├── Stock Counts (CRUD + adjustments)
└── Reports (Read-only analytics)

Step 2: Entity Relationship Map

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Product ──< ProductVariant >── Attribute
  │
  ├──< StockItem >── Warehouse
  │
  └──< PurchaseOrderLine >── PurchaseOrder >── Supplier

Step 3: CRUD Completeness Matrix

For EVERY entity, verify ALL operations:

Implementation Rules

NO Mock Implementations

Every function must contain REAL implementation logic:

typescriptCopy code
// ❌ FORBIDDEN - Mock/Placeholder
async getProducts() {
  return []; // TODO: implement
}

// ✅ REQUIRED - Real Implementation
async getProducts(filters: ProductFilters, pagination: Pagination): Promise<PaginatedResult<Product>> {
  const query = this.repository.createQueryBuilder('p')
    .leftJoinAndSelect('p.category', 'category')
    .leftJoinAndSelect('p.variants', 'variant');

  if (filters.categoryId) {
    query.andWhere('p.categoryId = :categoryId', { categoryId: filters.categoryId });
  }
  if (filters.search) {
    query.andWhere('(p.name ILIKE :search OR p.sku ILIKE :search)', { search: `%${filters.search}%` });
  }

  query.orderBy('p.createdAt', 'DESC');
  return query.paginate(pagination);
}

CRUD Pattern Requirements

Create

• Input validation with specific error messages
• Unique constraint checking before insert
• Default values applied
• Relationships validated (FK existence)
• Audit trail (createdBy, createdAt)

Read List

• Pagination (cursor or offset)
• Filtering by relevant fields
• Sorting by configurable columns
• Include counts and aggregates
• Field selection (don't return unnecessary data)

Read Detail

• Include related entities (eager loading)
• 404 handling with clear message
• Authorization check (user can access this resource)

Update

• Partial update support (PATCH semantics)
• Immutable fields protection (e.g., createdAt, id)
• Optimistic locking or version checking
• Audit trail (updatedBy, updatedAt)

Delete

• Soft delete by default (deletedAt timestamp)
• Cascade behavior explicitly defined
• Referential integrity check before delete
• Hard delete only via explicit admin endpoint

Domain-Driven Design Patterns

Entity Structure

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// Base entity with audit fields
interface BaseEntity {
  id: string; // UUID
  createdAt: Date;
  updatedAt: Date;
  deletedAt: Date | null; // Soft delete
  createdBy: string;
  updatedBy: string;
}

// Domain entity with business rules
class Product extends BaseEntity {
  // Fields
  name: string;
  sku: string;
  price: number;
  cost: number;
  status: ProductStatus;

  // Business rules in the entity
  activate(): void {
    if (this.price <= 0) throw new DomainError('Price must be positive');
    this.status = ProductStatus.ACTIVE;
  }

  calculateMargin(): number {
    return this.price - this.cost;
  }
}

Repository Pattern

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interface ProductRepository {
  findById(id: string): Promise<Product | null>;
  findList(
    filters: ProductFilters,
    page: Pagination
  ): Promise<PaginatedResult<Product>>;
  save(product: Product): Promise<Product>;
  softDelete(id: string): Promise<void>;
  restore(id: string): Promise<void>;
}

Sub-Module Detection Checklist

When building a module, check for these common sub-modules:

• Master Data: Core entities (Products, Customers, Vendors)
• Transactions: Business operations (Orders, Invoices, Movements)
• Configuration: Settings and preferences
• Reports: Read-only analytics and exports
• Audit Log: Change tracking
• Permissions: Role-based access per entity
• Notifications: Event-driven alerts
• Import/Export: Bulk data operations

Delivery Verification

Before marking a module complete:

• ALL sub-modules identified and listed in TODO
• EVERY entity has complete CRUD (no gaps)
• NO mock/placeholder implementations
• ALL relationships properly configured
• ALL business rules implemented (not stubbed)
• ALL validations in place
• Migration files created and tested
• Seed data exists for development
• API documentation complete
• Tests cover every endpoint

When NOT to Use

Do NOT use this skill when:

• Writing API endpoint implementations (use api-design skill)
• Reviewing code for quality issues (use code-review skill)
• Performing security audits (use security-auditor skill)
• Analyzing deployment configurations (use deployment skill)
• Writing SQL queries (use sql-best-practices skill)
• Designing database schemas (use database-design skill)
• Designing multi-page website layouts (use design-system skill)
• Reviewing git workflows (use git-workflow skill)