Step 1 — Setup, config, and the schema

1# 1. create the project
2mkdir expenses && cd expenses
3go mod init github.com/you/expenses
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 and files
12mkdir -p cmd/api internal/{config,database,httpx,middleware,user,expense} migrations
13touch cmd/api/main.go internal/config/config.go internal/database/db.go
14touch internal/httpx/json.go migrations/001_init.up.sql
15touch .env .env.example
16printf '.env\n' >> .gitignore
17
18# 4. a database
19docker run -d --name exp-pg \
20  -e POSTGRES_PASSWORD=secret -e POSTGRES_DB=expenses \
21  -p 5432:5432 postgres:16
22
23# 5. apply the schema
24docker exec -i exp-pg psql -U postgres -d expenses < migrations/001_init.up.sql
25
26# 6. check it
27docker exec -it exp-pg psql -U postgres -d expenses -c '\dt'
28docker exec -it exp-pg psql -U postgres -d expenses -c '\d expenses'
29
30# 7. run it, and prove the config check works
31go run ./cmd/api
32JWT_SECRET=short go run ./cmd/api        # must refuse to start

1package config
2
3import (
4	"errors"
5	"os"
6
7	"github.com/joho/godotenv"
8)
9
10type Config struct {
11	Port        string
12	DatabaseURL string
13	JWTSecret   []byte
14}
15
16func Load() (*Config, error) {
17	_ = godotenv.Load()          // loads .env in development; ignored in production
18
19	c := &Config{
20		Port:        env("PORT", "8080"),
21		DatabaseURL: os.Getenv("DATABASE_URL"),
22		JWTSecret:   []byte(os.Getenv("JWT_SECRET")),
23	}
24
25	// Check here, so a missing value stops the deploy instead of breaking a
26	// request later.
27	if c.DatabaseURL == "" {
28		return nil, errors.New("DATABASE_URL is required")
29	}
30	if len(c.JWTSecret) < 32 {
31		return nil, errors.New("JWT_SECRET must be at least 32 characters")
32	}
33
34	return c, nil
35}
36
37func env(key, fallback string) string {
38	if v := os.Getenv(key); v != "" {
39		return v
40	}
41	return fallback
42}

1PORT=8080
2DATABASE_URL=postgres://postgres:secret@localhost:5432/expenses?sslmode=disable
3JWT_SECRET=replace-me-with-32-or-more-random-characters

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,     -- CITEXT: A@x.com equals a@x.com
7  password_hash TEXT NOT NULL,              -- the hash, never the password
8  created_at    TIMESTAMPTZ NOT NULL DEFAULT now()
9);
10
11CREATE TABLE expenses (
12  id          BIGSERIAL PRIMARY KEY,
13  user_id     BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
14  amount_cents BIGINT NOT NULL CHECK (amount_cents > 0),
15  category    TEXT NOT NULL,
16  note        TEXT NOT NULL DEFAULT '',
17  spent_on    DATE NOT NULL,
18  created_at  TIMESTAMPTZ NOT NULL DEFAULT now()
19);
20
21-- the exact shape of "list my expenses, newest first"
22CREATE INDEX ON expenses (user_id, spent_on DESC);

1go get github.com/jackc/pgx/v5/stdlib     # Postgres driver
2go get golang.org/x/crypto/bcrypt         # password hashing
3go get github.com/golang-jwt/jwt/v5       # tokens
4go get github.com/joho/godotenv           # .env in development