CQRS — o‘qish va yozishni ajratish

Odatda bitta model (masalan, Order entity) ham yozuv, ham o‘qish uchun ishlatiladi.

CQRS tizimni ikki tomonga ajratadi — har biri mustaqil optimallashtiriladi.

Eng muhim tushuncha: CQRS — bu spektr, "hammasi yoki hech narsa" emas. Eng oddiy darajada — shunchaki kodni command va query qismlariga ajratasan (bitta baza). Eng kuchli darajada — alohida o‘qish ombori (denormalizatsiya, event bilan sinxron). Kichikdan boshlash mumkin.

Ikki tomonni aniq farqlash kerak — ular butunlay boshqacha xulq-atvorga ega:

NestJS’da CQRS uchun rasmiy modul bor: @nestjs/cqrs — CommandBus, QueryBus va handler’lar.

1 · Command va uning handleri

// COMMAND — niyat (imperative). @nestjs/cqrs
export class CreateOrderCommand {
  constructor(
    public readonly userId: string,
    public readonly items: OrderItem[],
  ) {}
}

@CommandHandler(CreateOrderCommand)
export class CreateOrderHandler implements ICommandHandler<CreateOrderCommand> {
  constructor(private prisma: PrismaService) {}
  async execute(cmd: CreateOrderCommand) {
    // validatsiya + biznes logika + YOZISH (write model)
    return this.prisma.order.create({
      data: { userId: cmd.userId, items: { create: cmd.items } },
    });
  }
}

2 · Query va uning handleri

// QUERY — ma'lumot so'raydi (side-effect yo'q), UI uchun moslangan DTO qaytaradi
export class GetUserOrdersQuery {
  constructor(public readonly userId: string) {}
}

@QueryHandler(GetUserOrdersQuery)
export class GetUserOrdersHandler implements IQueryHandler<GetUserOrdersQuery> {
  constructor(private prisma: PrismaService) {}
  async execute(q: GetUserOrdersQuery) {
    // o'qishga moslangan natija (denormalizatsiya qilingan view)
    return this.prisma.orderView.findMany({ where: { userId: q.userId } });
  }
}

3 · Controller — bus’lar orqali

// Controller — CommandBus va QueryBus orqali yo'naltiradi
@Controller('orders')
export class OrdersController {
  constructor(private commands: CommandBus, private queries: QueryBus) {}

  @Post()                                              // yozuv -> command
  create(@Body() dto: CreateOrderDto, @CurrentUser() userId: string) {
    return this.commands.execute(new CreateOrderCommand(userId, dto.items));
  }

  @Get()                                               // o'qish -> query
  list(@CurrentUser() userId: string) {
    return this.queries.execute(new GetUserOrdersQuery(userId));
  }
}

Read model qanday quriladi

Yozuv normalizatsiya qilingan asosiy bazaga boradi. Har yozuvda event chiqadi, va projection uni o‘qib, o‘qishga moslangan omborni (denormalizatsiya — JOIN’siz, tayyor) yangilaydi:

// PROJECTION: yozuv tomonidan event chiqadi -> o'qish modelini yangilaymiz
@EventsHandler(OrderCreatedEvent)
export class OrderProjection implements IEventHandler<OrderCreatedEvent> {
  constructor(private prisma: PrismaService) {}
  async handle(event: OrderCreatedEvent) {
    // o'qishga optimallashtirilgan jadval: JOIN'siz, hammasi TAYYOR
    await this.prisma.orderView.create({
      data: {
        orderId:  event.orderId,
        userId:   event.userId,
        userName: event.userName,    // DENORMALIZATSIYA: user nomi shu yerda saqlanadi
        total:    event.total,
        status:   'created',
      },
    });
  }
}

CQRS darajalari — kichikdan boshla

• 1-daraja (arzon): faqat kodni command/query handler’larga ajratish (bitta baza). Toza, testlanadigan — ko‘pchilik uchun shu yetadi.
• 2-daraja (o‘rta): o‘sha bazada alohida o‘qish modeli (denormalizatsiya qilingan view jadval).
• 3-daraja (qimmat): alohida o‘qish ombori (Redis/ES) + event bilan sinxron → pirovard izchillik.

• CQRS = o‘qish va yozish mas’uliyatini ajratish: Command (yozuv — o‘zgartiradi) va Query (o‘qish — qaytaradi). CQS prinsipining arxitektura darajasi.
• Sabab: o‘qish va yozish ehtiyojlari tubdan farq qiladi — yozuv izchillik/normalizatsiya, o‘qish tezlik/denormalizatsiya xohlaydi.
• NestJS: @nestjs/cqrs — CommandBus/QueryBus + handler’lar; controller yupqa qoladi.
• Kuchli ko‘rinish: alohida o‘qish modeli (projection), event bilan sinxron — lekin eventual consistency narxi bilan.
• CQRS — spektr: kod ajratishdan alohida omborgacha. Kichikdan boshla, oddiy CRUD uchun ishlatma.