golang-patterns

Golang Patterns Skill

Instructions for AI

Apply idiomatic Go patterns, modern best practices, and production-grade code standards. Use this skill when writing, reviewing, or refactoring Go code. Follow Go's philosophy: simplicity, clarity, composition.

Reference: Effective Go, Go Code Review Comments, Uber Go Style Guide.

Core Patterns

1. Repository Pattern with Interfaces

Abstraction over data access, enabling testability and swappable backends.

type OrderRepository interface {
    Create(ctx context.Context, order *Order) error
    GetByID(ctx context.Context, id uuid.UUID) (*Order, error)
    List(ctx context.Context, filter OrderFilter) ([]Order, error)
    Update(ctx context.Context, order *Order) error
    Delete(ctx context.Context, id uuid.UUID) error
}

// PostgreSQL implementation
type postgresOrderRepo struct {
    db *sql.DB
}

func NewPostgresOrderRepo(db *sql.DB) OrderRepository {
    return &postgresOrderRepo{db: db}
}

func (r *postgresOrderRepo) GetByID(ctx context.Context, id uuid.UUID) (*Order, error) {
    var o Order
    err := r.db.QueryRowContext(ctx,
        `SELECT id, customer_id, total, status, created_at
         FROM orders WHERE id = $1`, id,
    ).Scan(&o.ID, &o.CustomerID, &o.Total, &o.Status, &o.CreatedAt)

    if errors.Is(err, sql.ErrNoRows) {
        return nil, fmt.Errorf("order %s: %w", id, ErrNotFound)
    }
    if err != nil {
        return nil, fmt.Errorf("querying order %s: %w", id, err)
    }
    return &o, nil
}

2. Service Layer with Dependency Injection

Business logic encapsulated in services with injected dependencies.

type OrderService struct {
    repo   OrderRepository
    events EventPublisher
    logger *slog.Logger
}

func NewOrderService(repo OrderRepository, events EventPublisher, logger *slog.Logger) *OrderService {
    return &OrderService{repo: repo, events: events, logger: logger}
}

func (s *OrderService) PlaceOrder(ctx context.Context, cmd PlaceOrderCommand) (*Order, error) {
    order, err := NewOrder(cmd.CustomerID, cmd.Items)
    if err != nil {
        return nil, fmt.Errorf("creating order: %w", err)
    }

    if err := s.repo.Create(ctx, order); err != nil {
        return nil, fmt.Errorf("saving order: %w", err)
    }

    if err := s.events.Publish(ctx, "orders.placed", OrderPlacedEvent{
        OrderID:    order.ID,
        CustomerID: order.CustomerID,
        Total:      order.Total,
    }); err != nil {
        s.logger.WarnContext(ctx, "event publish failed", slog.String("error", err.Error()))
    }

    return order, nil
}