API Implementation Patterns

Template for project-specific API implementation skill Fill in [CUSTOMIZE] sections with your project's detected or chosen patterns

Project: [PROJECT NAME] Framework: [CUSTOMIZE: Spring Boot / Express.js / FastAPI / Django / Ruby on Rails / Gin] Language: [CUSTOMIZE: Java / TypeScript / Python / Ruby / Go] Last Updated: [DATE]

---

Controller/Route Layer

File Organization

Location: [CUSTOMIZE: src/main/java/controllers / src/controllers / app/routers]

Naming Convention: [CUSTOMIZE: UserController / UsersController / user_controller / user.routes]

Pattern Type: [CUSTOMIZE: Class-based / Function-based / Decorator-based]

Endpoint Definition Pattern

[CUSTOMIZE WITH YOUR PROJECT'S ACTUAL PATTERN]

Example - GET Endpoint:

[CUSTOMIZE: Show actual code pattern from your project]

Example patterns:
- Spring Boot: @GetMapping("/users")
- Express: router.get('/users', async (req, res) => {...})
- FastAPI: @router.get("/users")
- Django: viewsets.ModelViewSet
- Rails: resources :users

Example - POST Endpoint with Validation:

[CUSTOMIZE: Show create/post pattern]

Example - PUT/PATCH Endpoint:

[CUSTOMIZE: Show update pattern]

Example - DELETE Endpoint:

[CUSTOMIZE: Show delete pattern]

Request/Response Handling

Request Body Parsing: [CUSTOMIZE: @RequestBody / req.body / Request / request.data]

Response Format: [CUSTOMIZE: ResponseEntity / res.json() / JSONResponse / render]

Status Codes: [CUSTOMIZE: Which codes used - 200, 201, 204, 400, 404, 500]

---

Service Layer

File Organization

Location: [CUSTOMIZE: src/main/java/services / src/services / app/services]

Naming: [CUSTOMIZE: UserService / UsersService / user_service / UserService.ts]

Pattern: [CUSTOMIZE: Class-based / Function-based / Module-based]

Business Logic Pattern

[CUSTOMIZE WITH ACTUAL PATTERN]

Example - CRUD Operations:

[CUSTOMIZE: Show service class/module structure]

Example:
- Create: createUser(data) → validates, saves, returns
- Read: getUserById(id) → finds, throws if not found
- Update: updateUser(id, data) → finds, validates, updates
- Delete: deleteUser(id) → checks dependencies, deletes

Transaction Management

Approach: [CUSTOMIZE: @Transactional / BEGIN/COMMIT / context manager / transaction.atomic]

Isolation Level: [CUSTOMIZE: READ_COMMITTED / Default / Custom]

---

Data Access Layer

File Organization

Location: [CUSTOMIZE: src/main/java/repositories / src/repositories / app/models]

Naming: [CUSTOMIZE: UserRepository / UsersRepository / user_repository]

Pattern: [CUSTOMIZE: Spring Data JPA / Prisma / SQLAlchemy / ActiveRecord / Raw SQL]

Query Pattern

[CUSTOMIZE WITH ACTUAL PATTERN]

Standard Queries:

[CUSTOMIZE: Show query methods]

Examples:
- findById(id)
- findAll()
- save(entity)
- delete(id)

Custom Queries:

[CUSTOMIZE: How custom queries are defined]

Examples:
- Spring Data: findByEmail(email)
- Prisma: findMany({ where: {...}})
- SQLAlchemy: query.filter_by(email=email)

N+1 Query Prevention

Strategy: [CUSTOMIZE: @EntityGraph / .include() / select_related() / eager loading]

---

Data Models / Entities

File Organization

Location: [CUSTOMIZE: src/main/java/entities / src/models / app/models]

Naming: [CUSTOMIZE: User / UserEntity / user.model / User.java]

Field Naming

Convention: [CUSTOMIZE: camelCase / snake_case / PascalCase]

Examples:

• User ID: [userId / user_id / id]
• Email: [email / emailAddress / email_address]
• Created timestamp: [createdAt / created_at / dateCreated]

Relationships

Pattern: [CUSTOMIZE: @OneToMany / hasMany / ForeignKey / references]

Example:

[CUSTOMIZE: How relationships are defined]

Validation

Location: [CUSTOMIZE: Entity level / DTO level / Separate validators]

Approach: [CUSTOMIZE: Annotations / Decorators / Validator classes / Schemas]

---

DTOs / Serializers

File Organization

Location: [CUSTOMIZE: src/main/java/dto / src/dto / app/serializers]

Naming Convention: [CUSTOMIZE: UserDTO / UserResponse / CreateUserDTO / user_schema]

Request DTOs

Pattern: [CUSTOMIZE: Records / Classes / Interfaces / Pydantic models]

Example:

[CUSTOMIZE: Show CreateRequest pattern]

Validation: [CUSTOMIZE: @Valid / class-validator / Pydantic / Rails validations]

Response DTOs

Pattern: [CUSTOMIZE: Same as request / Separate / ViewModels]

Example:

[CUSTOMIZE: Show Response DTO]

Mapping

Approach: [CUSTOMIZE: Manual / MapStruct / class-transformer / Serializer]

---

Exception Handling

Custom Exceptions

Location: [CUSTOMIZE: src/exceptions / src/errors / app/exceptions]

Naming: [CUSTOMIZE: ResourceNotFoundException / NotFoundError / ResourceNotFound]

Example:

[CUSTOMIZE: Show custom exception]

Global Handler

Pattern: [CUSTOMIZE: @ControllerAdvice / middleware / exception_handler / rescue_from]

Error Response Format:

[CUSTOMIZE: Show your error response structure]
{
  "status": 404,
  "message": "User not found",
  "timestamp": "2025-12-30T10:00:00Z"
}

---

Testing Patterns

Unit Tests

Framework: [CUSTOMIZE: JUnit 5 / Jest / Pytest / RSpec]

Mocking: [CUSTOMIZE: Mockito / sinon / unittest.mock / RSpec mocks]

Test Structure: [CUSTOMIZE: AAA / Given-When-Then / Arrange-Act-Assert]

Example:

[CUSTOMIZE: Show unit test pattern]

Integration Tests

Framework: [CUSTOMIZE: Spring Test / Supertest / TestContainers / Django TestCase]

Database: [CUSTOMIZE: TestContainers / In-memory / Rollback / Fixtures]

Example:

[CUSTOMIZE: Show integration test]

---

API Documentation

Format

Approach: [CUSTOMIZE: OpenAPI/Swagger / JSDoc / Docstrings / YARD / Inline comments]

Mock Generation

Location: [CUSTOMIZE: api-mocks/ / mocks/ / fixtures/]

Format:

[CUSTOMIZE: Show mock structure]

---

Security Patterns

Input Validation

Where: [CUSTOMIZE: Controller / DTO / Middleware / Before filter]

How: [CUSTOMIZE: Annotations / Decorators / Manual checks / Validators]

SQL Injection Prevention

Approach: [CUSTOMIZE: Parameterized queries / ORM only / Prepared statements]

Authentication

Pattern: [CUSTOMIZE: JWT / Session / OAuth / API Keys]

---

Code Generation Checklist

When generating API code, always include:

• Controller with all endpoints (GET, POST, PUT, DELETE)
• Service layer with business logic
• Repository/Data access layer
• Entity/Model with proper fields
• Request DTOs with validation
• Response DTOs
• Custom exceptions for domain errors
• Global exception handler
• Unit tests (>80% coverage)
• Integration tests (API endpoints)
• API mocks for frontend
• [PROJECT-SPECIFIC ITEM]

---

Project-Specific Conventions

[CUSTOMIZE - ADD PROJECT GOTCHAS AND PREFERENCES]

Naming Conventions

• [e.g., Controllers always plural: UsersController not UserController]
• [e.g., Services always singular: UserService]

Code Review Requirements

• [e.g., All public methods must have JavaDoc]
• [e.g., Complex logic needs inline comments]

Performance Considerations

• [e.g., Always paginate list endpoints]
• [e.g., Use database indexes on foreign keys]

---

Customization Complete: Replace all [CUSTOMIZE] sections with project-detected or chosen patterns.

Auto-generated by:

/add-skill api-implementation-patterns

command (with code analysis)