NestJS API Standards & Common Patterns

Priority: P1 (OPERATIONAL)

Standardized API response patterns and common NestJS conventions.

Generic Response Wrapper

• Concept: Standardize all successful API responses.
• Implementation: Use TransformInterceptor to wrap data in { statusCode, data, meta }.

Response Mapping (Critical)

• [Rule] Zero-Entity Exposure: Controllers MUST NOT return raw ORM entities. Every endpoint must map its result to a dedicated Response DTO (e.g., plainToInstance(UserResponseDto, user)) to prevent accidental exposure of internal fields or circular dependencies.

Deep Validation (Critical)

• [Rule] Nested Validation: When a DTO property is an object or an array of objects, you MUST use @ValidateNested() along with @Type(() => TargetDto) from class-transformer to ensure deep validation.

Pagination Standards (Pro)

• DTOs: Use strict PageOptionsDto (page/take/order) and PageDto<T> (data/meta).
• Swagger Logic: Generics require ApiExtraModels and schema path resolution.
• Reference: See Pagination Wrapper Implementation for the complete ApiPaginatedResponse decorator code.

Custom Error Response

• Standard Error Object:

  export class ApiErrorResponse {
    @ApiProperty()
    statusCode: number;
  
    @ApiProperty()
    message: string;
  
    @ApiProperty()
    error: string;
  
    @ApiProperty()
    timestamp: string;
  
    @ApiProperty()
    path: string;
  }
  

• Docs: Apply @ApiBadRequestResponse({ type: ApiErrorResponse }) globally or per controller.

🚫 Anti-Patterns

• Do NOT use standard patterns if specific project rules exist.
• Do NOT ignore error handling or edge cases.