Step 1 — Setup and the schema

1# 1. create the project
2mkdir shop && cd shop
3go mod init github.com/you/shop
4
5# 2. dependencies
6go get github.com/jackc/pgx/v5/stdlib
7go get golang.org/x/crypto/bcrypt
8go get github.com/golang-jwt/jwt/v5
9go get github.com/joho/godotenv
10
11# 3. folders
12mkdir -p cmd/api
13mkdir -p internal/core/{domain,port,service}
14mkdir -p internal/adapter/handler/http/{middleware,httpx}
15mkdir -p internal/adapter/storage/{postgres,file}
16mkdir -p internal/adapter/auth
17mkdir -p internal/config
18mkdir -p migrations uploads
19echo "uploads/" >> .gitignore
20echo ".env"     >> .gitignore
21
22# 4. empty files, so the layout is visible before you fill them
23touch cmd/api/main.go
24touch internal/config/config.go internal/adapter/storage/postgres/db.go internal/adapter/handler/http/httpx/json.go
25touch migrations/001_init.up.sql
26touch .env .env.example
27
28# 5. a database
29docker run -d --name shop-pg \
30  -e POSTGRES_PASSWORD=secret -e POSTGRES_DB=shop \
31  -p 5432:5432 postgres:16
32
33# 6. the migration tool
34go install -tags 'postgres' github.com/golang-migrate/migrate/v4/cmd/migrate@latest

1PORT=8080
2DATABASE_URL=postgres://postgres:secret@localhost:5432/shop?sslmode=disable
3JWT_SECRET=change-me-to-at-least-32-random-characters
4UPLOAD_DIR=./uploads
5MAX_UPLOAD_MB=5

1CREATE EXTENSION IF NOT EXISTS citext;
2
3CREATE TABLE users (
4  id            BIGSERIAL PRIMARY KEY,
5  name          TEXT NOT NULL,
6  email         CITEXT UNIQUE NOT NULL,
7  password_hash TEXT NOT NULL,
8  role          TEXT NOT NULL DEFAULT 'customer'
9                CHECK (role IN ('customer', 'admin')),
10  created_at    TIMESTAMPTZ NOT NULL DEFAULT now()
11);
12
13CREATE TABLE products (
14  id          BIGSERIAL PRIMARY KEY,
15  name        TEXT NOT NULL,
16  description TEXT NOT NULL DEFAULT '',
17  price_cents BIGINT NOT NULL CHECK (price_cents >= 0),
18  stock       INT NOT NULL DEFAULT 0 CHECK (stock >= 0),
19  image_id    BIGINT,
20  active      BOOLEAN NOT NULL DEFAULT true,
21  created_at  TIMESTAMPTZ NOT NULL DEFAULT now()
22);
23
24CREATE TABLE images (
25  id          BIGSERIAL PRIMARY KEY,
26  stored_name TEXT NOT NULL,
27  mime        TEXT NOT NULL,
28  size_bytes  BIGINT NOT NULL,
29  created_at  TIMESTAMPTZ NOT NULL DEFAULT now()
30);
31
32CREATE TABLE cart_items (
33  id         BIGSERIAL PRIMARY KEY,
34  user_id    BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
35  product_id BIGINT NOT NULL REFERENCES products(id) ON DELETE CASCADE,
36  quantity   INT NOT NULL CHECK (quantity > 0),
37  UNIQUE (user_id, product_id)
38);
39
40CREATE TABLE orders (
41  id           BIGSERIAL PRIMARY KEY,
42  user_id      BIGINT NOT NULL REFERENCES users(id),
43  total_cents  BIGINT NOT NULL,
44  status       TEXT NOT NULL DEFAULT 'placed',
45  created_at   TIMESTAMPTZ NOT NULL DEFAULT now()
46);
47
48CREATE TABLE order_items (
49  id          BIGSERIAL PRIMARY KEY,
50  order_id    BIGINT NOT NULL REFERENCES orders(id) ON DELETE CASCADE,
51  product_id  BIGINT NOT NULL REFERENCES products(id),
52  name        TEXT NOT NULL,
53  price_cents BIGINT NOT NULL,
54  quantity    INT NOT NULL
55);
56
57CREATE INDEX ON orders (user_id, created_at DESC);

1# apply it
2migrate -path migrations -database "$DATABASE_URL" up
3
4# check
5docker exec -it shop-pg psql -U postgres -d shop -c '\dt'
6docker exec -it shop-pg psql -U postgres -d shop -c '\d products'
7
8# make yourself an admin later with:
9# UPDATE users SET role = 'admin' WHERE email = 'you@example.com';

1# The same code, but it moves to where this architecture expects it.
2cp    ../expenses/internal/config/config.go        internal/config/
3cp    ../expenses/internal/database/db.go          internal/adapter/storage/postgres/
4cp    ../expenses/internal/httpx/json.go           internal/adapter/handler/http/httpx/
5cp    ../expenses/internal/middleware/auth.go      internal/adapter/handler/http/middleware/
6cp    ../expenses/internal/user/user.go            internal/core/domain/user.go
7cp    ../expenses/internal/user/service.go         internal/core/service/user.go
8cp    ../expenses/internal/user/repository.go      internal/adapter/storage/postgres/user.go
9cp    ../expenses/internal/user/handler.go         internal/adapter/handler/http/user.go
10
11# then fix the module path in every copied file
12grep -rl 'github.com/you/expenses' internal/ | xargs sed -i 's|github.com/you/expenses|github.com/you/shop|g'
13
14go mod tidy
15go build ./...

1go run ./cmd/api
2# in another terminal
3curl -s localhost:8080/healthz
4curl -s -X POST localhost:8080/v1/auth/register \
5  -d '{"name":"Admin","email":"admin@shop.test","password":"password123"}'
6
7# promote that user to admin
8docker exec -it shop-pg psql -U postgres -d shop \
9  -c "UPDATE users SET role='admin' WHERE email='admin@shop.test';"