NestJS: the orders service

Structure for a growing team

As the API grows, NestJS gives every piece a place: controllers speak HTTP, services hold the rules, DTOs validate input, and Nest wires them together with dependency injection. Today you write the service — the heart of the orders feature.

orders.service.ts

import { BadRequestException, Injectable, NotFoundException } from "@nestjs/common";
import { CreateOrderDto } from "./order.dto";
import { PRICES } from "./prices";

export type Status = "new" | "cooking" | "ready";

export interface Order {
  id: number;
  dish: string;
  qty: number;
  total: number;
  status: Status;
}

const NEXT: Record<Status, Status | null> = { new: "cooking", cooking: "ready", ready: null };

@Injectable()
export class OrdersService {
  private orders: Order[] = [];

  create(dto: CreateOrderDto): Order {
    const price = PRICES[dto.dish];
    if (price === undefined) throw new BadRequestException(`Unknown dish: ${dto.dish}`);
    const order: Order = { id: this.orders.length + 1, dish: dto.dish, qty: dto.qty, total: price * dto.qty, status: "new" };
    this.orders.push(order);
    return order;
  }

  findAll(status?: Status): Order[] {
    return status ? this.orders.filter((o) => o.status === status) : this.orders;
  }

  findOne(id: number): Order {
    const order = this.orders.find((o) => o.id === id);
    if (!order) throw new NotFoundException(`Order ${id} not found`);
    return order;
  }

  advance(id: number): Order {
    const order = this.findOne(id);
    const next = NEXT[order.status];
    if (!next) throw new BadRequestException("Order already ready");
    order.status = next;
    return order;
  }
}

Structure for a growing team

orders.service.ts

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