Nestjs Patterns

Rules

• Separate controller, service, dto, and schema concerns strictly.
• Controllers route only — thin. Services hold all logic and are testable.
• Validate incoming data with DTOs + class-validator. Document with @ApiProperty.
• Add tests close to behavior changes when risk is non-trivial.

Module / Controller / Service

// Module
@Module({
  imports: [MongooseModule.forFeature([{ name: Resource.name, schema: ResourceSchema }])],
  controllers: [ResourceController],
  providers: [ResourceService],
})
export class ResourceModule {}

// Controller
@Get(':id')
@ApiResponse({ status: 200, type: ResourceResponseDto })
async findOne(@Param('id') id: string): Promise<ResourceResponseDto> {
  return this.resourceService.findOne(id);
}

// Service
async findOne(id: string): Promise<ResourceResponseDto> {
  const doc = await this.model.findById(id).lean().exec();
  if (!doc) throw new NotFoundException(`Resource ${id} not found`);
  return plainToInstance(ResourceResponseDto, doc);
}