How to Implement Domain-Driven Design (DDD) in Go

Implement Domain-Driven Design in Go by organizing your code into bounded contexts with clear interfaces and separating domain logic from infrastructure. Start by defining your core domain entities and interfaces in a domain package, then implement application services and infrastructure handlers in separate layers.

// domain/user.go
package domain

type User interface {
    ID() string
    Name() string
}

type UserService interface {
    GetByID(id string) (User, error)
}

// application/user_service.go
package application

import "yourapp/domain"

type userService struct {
    repo domain.UserRepository
}

func NewUserService(repo domain.UserRepository) domain.UserService {
    return &userService{repo: repo}
}

func (s *userService) GetByID(id string) (domain.User, error) {
    return s.repo.FindByID(id)
}

// infrastructure/postgres/user_repo.go
package postgres

import "yourapp/domain"

type userRepository struct {
    db *sql.DB
}

func NewUserRepository(db *sql.DB) domain.UserRepository {
    return &userRepository{db: db}
}

func (r *userRepository) FindByID(id string) (domain.User, error) {
    // SQL implementation here
    return nil, nil
}

DDD in Go means organizing your code so business rules live in one place and database or API code lives in another. Think of it like a restaurant where the chef (domain) knows the recipes, but the waiter (application) takes orders and the kitchen staff (infrastructure) handles the cooking tools. This keeps your code clean and makes it easier to change how you store data without breaking your business logic.