Django Gone Clean Jairo Vadillo Martín Backend Lead @ 21buttons 

21 Buttons is the first fashion social-commerce app in the world AD +22M Monthly visits +8M App download in 6 countries +25K Daily posts +3500 Influencers +50k Daily products tagged +2000 Brands tagged 

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☎ Past Present Future 

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☎ Messy Everything in place but… Different styles 

Standardised Old stuff deprecated Different services 

MOAR: Features Developers Microservices Microframeworks Programming languages 

Django + DRF 

views.py serializers.py admin.py models.py 

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Django Django Django Django Django Django Django Django Django Django Django Django Django Django Django Django Django Django Django Django Django 

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✨Django Gone Clean 

✨ Code that’s: Scalable Easy to understand Fully testable 

✨ 

✨ Writing only integration tests Staying with Django while creating more micro services 

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✨ views.py services.py use_cases.py entities.py repositories.py factories.py admin.py models.py 

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✨ ENTITIES Entities encapsulate Enterprise wide business rules Entities vs. Django models @dataclass class User: id: str name: str email: str 

✨ # services.py class PublicationsService: def has_edit_permission(request_user_id: int, publication: Publication): pass SERVICES 

✨ USE CASES Contains application specific business rules Responsibilities: Communicate with repositories Manage permissions Trigger side effects Handle or raise exceptions 

✨ USE CASES class CreateUserUseCase: def __init__(user_repo, user_service): self._user_repo = user_repo self._user_service = user_service def execute(user_data: UserData) -> User: # do stuff user_repo.create(user_dto) # do more stuff 

✨ USE CASES @patch('users.repositories.UsersRepo') @patch('users.events.EventManager') @patch('users.tasks.UserTasks') @patch('users.services.UsersService') def test_repo_called(): ... @pytest.mark.unit class TestCreateUserUseCase: def test_repo_called(): repo = Mock() event_manager = Mock() service = Mock() tasks = Mock() use_case = CreateUserUseCase(...) 

✨ USE CASES # use_cases.py class CreateUserUseCase: ... def execute(user_dto) -> User: ... event_manager.trigger(UserCreatedEvent(user)) # users/events.py @dataclass class UserCreatedEvent: user: User 

✨ USE CASES # download_registers/apps.py from django.apps import AppConfig class DownloadRegistersConfig(AppConfig): name = 'download_registers' verbose_name = "Download Registers" def ready(self): from .subscribers import compute_rewards from users.events import UserCreatedEvent EventManager.subscribe(compute_rewards, UserCreatedEvent) # download_registers/subscribers.py def compute_rewards(event: UserCreatedEvent): # run task to compute rewards 

✨ USE CASES Use cases & Microservices 

✨ factories.py 

✨ FACTORIES & CONF Factories? In python? WHY? from .use_cases import CreateUserUseCase from .repositories import UsersRepo def build_create_user_use_case() -> CreateUserUseCase: return CreateUserUseCase(UsersRepo(db_connection)) 

✨ views.py repositories.py admin.py models.py 

✨ REPOSITORIES Only layer that knows about data sources Responsibilities: Guarantee the correct communication with data sources 

✨ class UserRepository: def __init__(db_repo, elastic_repo): self._db_repo = db_repo self._elastic_repo = elastic_repo def get(self, id): return self._db_repo.get(id) def search(self, query): return self._elastic_repo.search(query) REPOSITORIES 

✨ class UserDBRepository: def get(self, id): user = User.objects.get(id=id) # parse user to entity return user class UserElasticRepository: def search(self, query): users = elasticsearch.query() # parse elastic users to entities return users REPOSITORIES 

✨ @pytest.mark.integration @pytest.mark.django_db class TestUserDBRepository: def test_get_user(): # create user to db (using fixtures for example) u = UserDBRepository().get(user_id) assert u == REPOSITORIES 

Handle the Rest API entry-point Responsibilities: Validate input data Call use cases Return results or errors ✨ VIEWS 

# dtos.py @dataclass class CreateUserRequestDTO: username: str email: str # validators.py from marshmallow import Schema, fields, validate, post_load class CreateUserSerializer(Schema): username = fields.String(required=True) email = fields.Email(required=True) @post_load def build_create_user_dto(self, data): return CreateUserRequestDTO(**data) ✨ VIEWS 

✨ VIEWS class CreateUserView(APIView): def post(self, request): user_dto, errors = CreateUserSerializer().load(request.data) if errors: return Response(errors, status=status.HTTP_400_BAD_REQUEST) use_case = build_create_user_use_case() try: user = use_case.execute(user_dto) except (UsernameAlreadyExistsError) as e: return Response(str(e), status=status.HTTP_422_UNPROCESSABLE_ENTITY) except PermissionsInsuficientException as e: return Response(str(e), status=status.HTTP_403_FORBIDDEN) else: return Response(UserSerializer().dump(user).data, status=status.HTTP_201_CREATED) 

✨ VIEWS class CreateUserView(APIView): def post(self, request): user_dto, errors = CreateUserSerializer().load(request.data) if errors: return Response(errors, status=status.HTTP_400_BAD_REQUEST) use_case = build_create_user_use_case() try: user = use_case.execute(user_dto) except (UsernameAlreadyExistsError) as e: return Response(str(e), status=status.HTTP_422_UNPROCESSABLE_ENTITY) except PermissionsInsuficientException as e: return Response(str(e), status=status.HTTP_403_FORBIDDEN) else: return Response(UserSerializer().dump(user).data, status=status.HTTP_201_CREATED) VALIDATE INPUT 

✨ CONTROLLERS class CreateUserView(APIView): def post(self, request): user_dto, errors = CreateUserSerializer().load(request.data) if errors: return Response(errors, status=status.HTTP_400_BAD_REQUEST) use_case = build_create_user_use_case() try: user = use_case.execute(user_dto) except (UsernameAlreadyExistsError) as e: return Response(str(e), status=status.HTTP_422_UNPROCESSABLE_ENTITY) except PermissionsInsuficientException as e: return Response(str(e), status=status.HTTP_403_FORBIDDEN) else: return Response(UserSerializer().dump(user).data, status=status.HTTP_201_CREATED) CALL USE CASE VALIDATE INPUT VIEWS 

✨ CONTROLLERS class CreateUserView(APIView): def post(self, request): user_dto, errors = CreateUserSerializer().load(request.data) if errors: return Response(errors, status=status.HTTP_400_BAD_REQUEST) use_case = build_create_user_use_case() try: user = use_case.execute(user_dto) except (UsernameAlreadyExistsError) as e: return Response(str(e), status=status.HTTP_422_UNPROCESSABLE_ENTITY) except PermissionsInsuficientException as e: return Response(str(e), status=status.HTTP_403_FORBIDDEN) else: return Response(UserSerializer().dump(user).data, status=status.HTTP_201_CREATED) HANDLE EXCEPTIONS CALL USE CASE VALIDATE INPUT VIEWS 

✨ CONTROLLERS class CreateUserView(APIView): def post(self, request): user_dto, errors = CreateUserSerializer().load(request.data) if errors: return Response(errors, status=status.HTTP_400_BAD_REQUEST) use_case = build_create_user_use_case() try: user = use_case.execute(user_dto) except (UsernameAlreadyExistsError) as e: return Response(str(e), status=status.HTTP_422_UNPROCESSABLE_ENTITY) except PermissionsInsuficientException as e: return Response(str(e), status=status.HTTP_403_FORBIDDEN) else: return Response(UserSerializer().dump(user).data, status=status.HTTP_201_CREATED) HANDLE EXCEPTIONS CALL USE CASE VALIDATE INPUT RETURN SERIALISED DATA VIEWS 

✨ CONTROLLERS @pytest.mark.unit class TestCreateUserView: @patch('users.views.build_create_user_use_case') def test_patch_failed_404(self, use_case_factory): use_case = MagicMock() use_case_factory.return_value = use_case use_case.execute.side_effect = BadContentUserDoesNotExist() request = MagicMock() response = BadContentUserDetailView().patch(request, user_id=1) assert response.status_code == 404 VIEWS 

def get_actions(self, request): return { 'delete_selected': ( self.delete_selected, 'delete_selected', 'Delete selected %(verbose_name_plural)s' ) } ✨ ADMIN 

def get_actions(self, request): return { 'delete_selected': ( self.delete_selected, 'delete_selected', 'Delete selected %(verbose_name_plural)s' ) } IT WORKS ✨ ADMIN 

✨ Integration tests 

Conclusions 

We
 are
 hiring 

⁉ Questions @jairovadillo 

*Audience gives a spontaneous big round of applause*