Go Backend: Orders API

Tip

Build this project yourself, step by step, on Codealong.

This repository is the finished code. In the Backend API Development course you build it lesson by lesson: start with your own server on net/http, move to a layered architecture that scales, then add orders with stock reservation. Pause the video, change the code, run it, and get instant feedback on each challenge.

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A small REST API for users, products and orders, written in Go as part of the Backend API Development course on Codealong.

It uses only the standard library (net/http with method-and-path routing) plus google/uuid. Data is kept in memory, so you can run it with no database or other setup.

What it covers

• A layered structure for each domain: handler (HTTP) → service (business rules) → repository (storage).
• Repository interfaces with in-memory implementations, so a real database can be added later without touching the services.
• Placing an order across domains: the order service checks that the customer and products exist, then reserves stock before it saves the order.
• All-or-nothing stock reservation: every line item is checked before any stock is taken, under a single lock.
• The same JSON shape for every response, for both success and error.

Requirements

• Go 1.26 or newer

Getting started

git clone https://github.com/codealong-dev/go-backend-ecom.git
cd go-backend-ecom
go run ./api

The server listens on http://localhost:8080. Everything is stored in memory, so data resets each time you restart the server. Some demo data is loaded at startup (see Seed data).

Project structure

.
├── api/
│   └── main.go              # wiring: repositories → services → handlers, seed, start server
└── internal/
    ├── platform/httpx/      # JSON response helpers shared by every handler
    ├── user/
    ├── product/
    └── order/

Each domain package follows the same layout:

File	Responsibility
<domain>.go	Entity types, request types and errors
handler.go	Route registration, request decoding, maps errors to HTTP status codes
service.go	Business rules and the Repository interface
memory.go	In-memory Repository, safe for concurrent use with sync.RWMutex
seed.go	Demo data loaded at startup (users and products only)

API

Every response is JSON with one of two shapes:

{ "data": ... }

{ "error": "message" }

Prices are whole numbers in cents (2499 = 24.99).

Method	Path	Description
GET	/users	List users
POST	/users	Create a user
GET	/users/{id}	Get a user by ID
GET	/products	List products and current stock
POST	/orders	Place an order
GET	/orders/{id}	Get an order by ID

Examples

List products:

curl localhost:8080/products

Create a user:

curl -X POST localhost:8080/users \
  -d '{"name": "Grace"}'

{"data":{"id":"ce81b23d-fa43-4fd1-b879-64cf7dea1001","name":"Grace"}}

Place an order for the seeded customer:

curl -X POST localhost:8080/orders \
  -d '{
    "customer_id": "9a8b7c6d-5e4f-4a3b-8c2d-000000000001",
    "items": [
      { "product_id": "7c1e4d2a-3b5f-4e8a-9c6d-000000000001", "quantity": 2 }
    ]
  }'

{
  "data": {
    "id": "92ffbde5-9d71-4cdc-8e5c-d032661a2536",
    "status": "pending",
    "items": [
      {
        "id": "ce1181e3-0c92-4391-9682-384374fbe494",
        "product_id": "7c1e4d2a-3b5f-4e8a-9c6d-000000000001",
        "order_id": "92ffbde5-9d71-4cdc-8e5c-d032661a2536",
        "price": 2499,
        "quantity": 2,
        "created_at": "2026-10-24T18:13:14.66855Z"
      }
    ],
    "customer_id": "9a8b7c6d-5e4f-4a3b-8c2d-000000000001",
    "created_at": "2026-10-24T18:13:14.668552Z"
  }
}

Fetch it back with the returned ID:

curl localhost:8080/orders/92ffbde5-9d71-4cdc-8e5c-d032661a2536

Each order item stores the product's price at the moment the order was placed, so changing a product's price later does not change past orders.

Errors

Status	When
400	Invalid JSON, missing name / customer_id / items, or an order ID that is not a UUID
404	User or order not found
422	The order refers to a customer or product that does not exist

Seed data

User

ID	Name
9a8b7c6d-5e4f-4a3b-8c2d-000000000001	Ada

Products

ID	Name	Price	Stock
7c1e4d2a-3b5f-4e8a-9c6d-000000000001	Wireless Mouse	2499	25
7c1e4d2a-3b5f-4e8a-9c6d-000000000002	Mechanical Keyboard	8999	3
7c1e4d2a-3b5f-4e8a-9c6d-000000000003	27-inch Monitor	22900	5
7c1e4d2a-3b5f-4e8a-9c6d-000000000004	USB-C Hub	3999	0

The USB-C Hub starts with no stock, so you can try ordering something that is out of stock.

License

MIT