Nestjs API Standards

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: Define ApiErrorResponse with statusCode, message, error, timestamp, path. See Error Response Class.
• Docs: Apply @ApiBadRequestResponse({ type: ApiErrorResponse }) globally or per controller.

Anti-Patterns

• No raw entity returns: Always map to a Response DTO; raw entities leak internal fields.
• No unvalidated nested DTOs: Use @ValidateNested() + @Type() for all nested object properties.
• No generic 200 docs: Apply @ApiResponse({ status, type }) with exact types per endpoint.

References

• Pagination Wrapper
• Error Response Class