NestJS Module Architecture

This skill defines the responsibilities of the core module files. A module consists of:

1. Service (.service.ts): Business logic, calculations, and DTO transformation.
2. Controller (.controller.ts): HTTP routing, documentation (Swagger), and request delegation.
3. Module (.module.ts): Dependency Injection wiring.

---

1. Service Pattern (.service.ts)

Responsibilities:

• Injects the Repository to access data.
• Implements business rules (e.g., hashing passwords, sanitizing inputs).
• Transforms raw database results into clean objects (e.g., removing sensitive fields).
• Throws HTTP exceptions (NotFoundException, ConflictException).
• NEVER accesses the database directly (always use the Repository).

Example: user.service.ts

import { Injectable, NotFoundException } from "@nestjs/common";
import { UserRepository } from "@repositories/user.repository";
import { UserCreateDto } from "./dto/user-create.dto";
import * as bcrypt from "bcrypt";

@Injectable()
export class UserService {
  constructor(private readonly userRepository: UserRepository) {}

  async create(dto: UserCreateDto) {
    try {
      // Business Logic: Hash password
      const hashedPassword = await bcrypt.hash(dto.password, 10);
      const fullName = `${dto.firstName} ${dto.lastName}`;

      // Call Repository
      const user = await this.userRepository.create({
        ...dto,
        password: hashedPassword,
        fullName,
      });

      // Sanitization
      const { password, ...cleanUser } = user;
      return cleanUser;
    } catch (error) {
      // Handle known errors
      throw error;
    }
  }
}

---

2. Controller Pattern (.controller.ts)

Responsibilities:

• Defines routes and HTTP verbs (@Get, @Post, etc.).
• Documents the API using Swagger (@ApiTags, @ApiOperation, @ApiResponse).
• Validates inputs using DTOs (@Body, @Query).
• Strictly delegates logic to the Service.
• Returns the Service's result directly.
• NEVER use any in DTOs or parameters; proper typing is required for Swagger to generate documentation and validation correctly.

Example: user.controller.ts

import { Controller, Get, Post, Body, Query, UseGuards } from "@nestjs/common";
import {
  ApiTags,
  ApiOperation,
  ApiResponse,
  ApiBearerAuth,
} from "@nestjs/swagger";
import { UserService } from "./user.service";
import { UserListDto, UserListFiltersDto } from "./dto/user-list.dto";
import { UserCreateDto } from "./dto/user-create.dto";
import { HttpErrorDto } from "@models/http-error.dto";

@ApiTags("user")
@ApiBearerAuth()
@Controller("admin/user")
export class UserController {
  constructor(private readonly userService: UserService) {}

  @Get("find-all")
  @ApiOperation({ summary: "Get all users paginated" })
  @ApiResponse({ status: 200, type: UserListDto })
  @ApiResponse({ status: 400, type: HttpErrorDto })
  findAll(@Query() filters: UserListFiltersDto) {
    return this.userService.findAllPaginated(filters);
  }

  @Post("create")
  @ApiOperation({ summary: "Create a new user" })
  @ApiResponse({ status: 200, type: UserListDto }) // Returns generic object, refine type as needed
  @ApiResponse({ status: 400, type: HttpErrorDto })
  create(@Body() dto: UserCreateDto) {
    return this.userService.create(dto);
  }
}

---

3. Module Wiring (.module.ts)

Responsibilities:

• Registers Controllers and Providers (Services, Repositories).
• Exports Services/Repositories if they need to be used by other modules.

Example: user.module.ts

import { Module } from "@nestjs/common";
import { UserService } from "./user.service";
import { UserController } from "./user.controller";
import { UserRepository } from "@repositories/user.repository";

@Module({
  controllers: [UserController],
  providers: [UserService, UserRepository],
  exports: [UserService, UserRepository],
})
export class UserModule {}

---

Global Models

Common DTOs like error responses should be placed in src/models/.

File: src/models/http-error.dto.ts

import { ApiProperty } from "@nestjs/swagger";

export class HttpErrorDto {
  @ApiProperty({
    description: "Error message(s)",
    example: ["Validation failed"],
  })
  message: string | string[];

  @ApiProperty({ description: "Error type", example: "Bad Request" })
  error: string;

  @ApiProperty({ description: "Status code", example: 400 })
  statusCode: number;
}