Don't start with a database Practical clean architecture Who I am - - PowerPoint PPT Presentation

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Don't start with a database Practical clean architecture Who I am - - PowerPoint PPT Presentation

Feb 15, 2023 2.01k likes •3.06k views

Don't start with a database Practical clean architecture Who I am Grzegorz Kocjan Goal of this talk P R O T I P # 0 New in Python Typing def get(order_id: int) -> dict: order_name: str = 'EuroPython2019!' order: dict = { 'id':

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Don't start with a database

Practical clean architecture

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Who I am

Grzegorz Kocjan

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Goal of this talk

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P R O T I P #

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New in Python

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Typing

def get(order_id: int) -> dict:

  • rder_name: str = 'EuroPython2019!'
  • rder: dict = {

'id': order_id, 'name': order_name } return order

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Typing

def get(order_id: int) -> dict:

  • rder_name: str = 'EuroPython2019!'
  • rder: dict = {

'id': order_id, 'name': order_name } return order

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Typing

def get(order_id: int) -> dict:

  • rder_name: str = 'EuroPython2019!'
  • rder: dict = {

'id': order_id, 'name': order_name } return order

P R O T I P # 1

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Typing

from typing import Dict, Union Order = Dict[str, Union[int,str]] def get(order_id: int) -> Order:

  • rder_name: str = 'EuroPython2019!'
  • rder: Order = {

'id': order_id, 'name': order_name } return order

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Typing

from typing import Dict, Union Order = Dict[str, Union[int,str]] def get(order_id: int) -> Order:

  • rder_name: str = 'EuroPython2019!'
  • rder: Order = {

'id': order_id, 'name': order_name } return order

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Typing

from typing import Dict, Union Order = Dict[str, Union[int,str]] def get(order_id: int) -> Order:

  • rder_name: str = 'EuroPython2019!'
  • rder: Order = {

'id': order_id, 'name': order_name } return order

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Typing

from typing import Dict, Union Order = Dict[str, Union[int,str]] def get(order_id: int) -> Order:

  • rder_name: str = 'EuroPython2019!'
  • rder: Order = {

'id': order_id, 'name': order_name } return order

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Python 3.7

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Dataclasses

from dataclasses import dataclass @dataclass class Order: id: int name: str

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Typing 💛 Dataclasses

from our_package.entities import Order def get(order_id: int) -> Order:

  • rder_name: str = EuroPython2019!'
  • rder: Order = Order(

id=order_id, name=order_name, ) return order

P R O T I P # 2

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Let's talk architecture

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How to design architecture?

With the idea of maintaining it for the next 10 years

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Clean architecture

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Time for “coding”

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Shop project - requirements

  • Creating orders
  • Viewing order lists
  • Add existing items to order
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Steps of building the application

  • data definition - entities
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Entities

class BaseEntity: pass @dataclass(frozen=True) class Client(BaseEntity): id: int name: str

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Entities

class BaseEntity: pass @dataclass(frozen=True) class Client(BaseEntity): id: int name: str

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Entities - frozen=True

>>> client = Client(id=1, name='Grzegorz') >>> client.name = 'Alice' Traceback (most recent call last): File "<input>", line 1, in <module> File "<string>", line 3, in __setattr__ dataclasses.FrozenInstanceError: cannot assign to field 'name'

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Entities

@dataclass(frozen=True) class Product(BaseEntity): id: int name: str price: float

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Entities

@dataclass(frozen=True) class Order(BaseEntity): id: int created: datetime client: Client total_cost: float = 0.0 items: ??

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Entities

@dataclass(frozen=True) class Order(BaseEntity): id: int created: datetime client: Client total_cost: float = 0.0 items: List[Product] = field(default_factory=list)

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Steps of building the application

  • data definition - entities
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Steps of building the application

  • data definition - entities
  • use cases
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Use cases

class OrderLogic: def create(self, client_id: int) -> Order: ... def search(self, client_id: int) -> List[Order]: ... def add_product(self, order_id: int, product_id: int) -> Order: ...

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But those are

  • perations on a

database …

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… it's time to introduce ...

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An abstraction

PRO TIP #3

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Clean architecture

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Repositories

class IClientRepository(abc.ABC): @abc.abstractmethod def create(self, name: str) -> Client: pass @abc.abstractmethod def get(self, client_id: int) -> Client: pass

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Repositories

class IClientRepository(abc.ABC): @abc.abstractmethod def create(self, name: str) -> Client: pass @abc.abstractmethod def get(self, client_id: int) -> Client: pass

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Repositories

class IClientRepository(abc.ABC): @abc.abstractmethod def create(self, name: str) -> Client: pass @abc.abstractmethod def get(self, client_id: int) -> Client: pass

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Repositories

class IClientRepository(abc.ABC): @abc.abstractmethod def create(self, name: str) -> Client: pass @abc.abstractmethod def get(self, client_id: int) -> Client: pass

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Repositories

class IClientRepository(abc.ABC): @abc.abstractmethod def create(self, name: str) -> Client: pass @abc.abstractmethod def get(self, client_id: int) -> Client: pass

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Repositories

class IClientRepository(abc.ABC): @abc.abstractmethod def create(self, name: str) -> Client: pass @abc.abstractmethod def get(self, client_id: int) -> Client: pass

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Repositories

class IProductRepository(abc.ABC): @abc.abstractmethod def get(self, product_id: int) -> Product: pass

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Repositories

class IOrderRepository(abc.ABC): def create(self, client: Client) -> Order: def get(self, order_id: int) -> Order: def save(self, order: Order) -> Order: def search( self, client: Optional[Client] = None ) -> List[Order]:

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Use cases

class OrderLogic: def create(self, client_id: int) -> Order: ... def search(self, client_id: int) -> List[Order]: ... def add_product(self, order_id: int, product_id: int) -> Order: ...

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Use cases

class OrderLogic: def __init__( self,

  • rders: IOrderRepository,

products: IProductRepository, clients: IClientRepository, ) -> None: self._orders: IOrderRepository = orders self._products: IProductRepository = products self._clients: IClientRepository = clients

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Use cases

class OrderLogic: @inject def __init__( self,

  • rders: IOrderRepository,

products: IProductRepository, clients: IClientRepository, ) -> None: self._orders: IOrderRepository = orders self._products: IProductRepository = products self._clients: IClientRepository = clients from injector import inject

P R O T I P # 4

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Use cases

class OrderLogic: def search(self, client_id: int) -> List[Order]: client = self._clients.get(client_id) return self._orders.search(client=client) def create(self, client_id: int) -> Order: client = self._clients.get(client_id) return self._orders.create(client=client)

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Use cases

class OrderLogic: def add_product(self, order_id: int, product_id: int) -> Order:

  • rder = self._orders.get(order_id)

product = self._products.get(product_id)

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Use cases

class OrderLogic: def add_product(self, order_id: int, product_id: int) -> Order:

  • rder = self._orders.get(order_id)

product = self._products.get(product_id)

  • rder = replace( # from dataclasses import replace
  • rder,

items=order.items + [product], total_cost=order.total_cost + product.price, )

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Use cases

class OrderLogic: def add_product(self, order_id: int, product_id: int) -> Order:

  • rder = self._orders.get(order_id)

product = self._products.get(product_id)

  • rder = replace( # from dataclasses import replace
  • rder,

items=order.items + [product], total_cost=order.total_cost + product.price, ) return self._orders.save(order)

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So much work…

why bother?

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Tests

def test_add_product_increases_order_total_cost( ) -> None:

P R O T I P # 5

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Tests

def test_add_product_increases_order_total_cost( prepare_repositories: StaticRepositories ) -> None: StaticRepositories = Tuple[ IOrderRepository, IProductRepository, IClientRepository ]

PRO TIP #6

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Tests

def test_add_product_increases_order_total_cost( prepare_repositories: StaticRepositories ) -> None:

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Tests

def test_add_product_increases_order_total_cost( prepare_repositories: StaticRepositories ) -> None: 1: logic = OrderLogic(*prepare_repositories) 2: order = logic.add_product(order_id=1, product_id=1) 3: assert order.total_cost == 100

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Steps of building the application

  • data definition - entities
  • use cases
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Steps of building the application

  • data definition - entities
  • use cases
  • implement interfaces
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Time for a database?

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No no no :)

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A repository

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A repository

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A repository in

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A repository in

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A repository in memory

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Repozytorium w pamięci

class RamStorage(Generic[T]): def __init__(self) -> None: self._storage: StorageType = {} T = TypeVar("T") StorageType = Dict[int, T] RamStorage[Client]() RamStorage[Order]()

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Repozytorium w pamięci

class RamStorage(Generic[T]): def __init__(self) -> None: self._storage: StorageType = {} def add(self, item: T) -> None: def get(self, pk: int) -> Optional[T]: def search(self, **kwargs: Any) -> RamStorage[T]: def remove(self, item: T) -> None: def all(self) -> List[T]:

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Repozytorium w pamięci - wykorzystanie

class ProductRepository(IProductRepository): def __init__(self) -> None: self._ram_storage = RamStorage[Product]()

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Repozytorium w pamięci - wykorzystanie

class ProductRepository(IProductRepository): def __init__(self) -> None: self._ram_storage = RamStorage[Product]() def get(self, product_id: int) -> Product: result = self._ram_storage.get(product_id) if result is None: raise ProductNotFound() return result

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Steps of building the application

  • data definition - entities
  • use cases
  • implement interfaces
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Steps of building the application

  • data definition - entities
  • use cases
  • implement interfaces
  • API
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Choose framework!

and this is slide no 77!

P R O T I P # 7

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Flask + Connexion

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Flask + connexion - api.yaml

paths: /orders/search/: get:

  • perationId: our_package.endpoints.search

parameters: ... responses: ...

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Flask + connexion - api.yaml

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Flask + connexion - endpoints

def search(logic: OrderLogic, client_id: int) -> List[Order]: return logic.search(client_id=client_id) def create(logic: OrderLogic, body: dict) -> Order: return logic.create(client_id=body['client_id']) def add_product(logic: OrderLogic, order_id: int, product_id: int) -> Order: return logic.add_product(order_id, product_id)

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Flask + connexion - endpoints

def search(logic: OrderLogic, client_id: int) -> List[Order]: return logic.search(client_id=client_id) def create(logic: OrderLogic, body: dict) -> Order: return logic.create(client_id=body['client_id']) def add_product(logic: OrderLogic, order_id: int, product_id: int) -> Order: return logic.add_product(order_id, product_id)

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Injector

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Flask + connexion - endpoints

flask_injector = FlaskInjector( app=app, modules=[MyModule] ) app.config["FLASK_INJECTOR"] = flask_injector

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Flask + connexion - endpoints

class MyModule(injector.Module): def configure(self, binder: injector.Binder) -> None:

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Flask + connexion - endpoints

class MyModule(injector.Module): def configure(self, binder: injector.Binder) -> None: binder.bind(OrderLogic, to=OrderLogic)

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Flask + connexion - endpoints

class MyModule(injector.Module): def configure(self, binder: injector.Binder) -> None: binder.bind(OrderLogic, to=OrderLogic) binder.bind( IClientRepository, to=ClientRepository, scope=injector.SingletonScope )

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Flask + connexion - endpoints

def search(logic: OrderLogic, client_id: int) -> List[Order]: return logic.search(client_id=client_id) def create(logic: OrderLogic, body: dict) -> Order: return logic.create(client_id=body['client_id']) def add_product(logic: OrderLogic, order_id: int, product_id: int) -> Order: return logic.add_product(order_id, product_id)

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Flask + connexion - endpoints

def search(logic: OrderLogic, client_id: int) -> List[Order]: return logic.search(client_id=client_id) def create(logic: OrderLogic, body: dict) -> Order: return logic.create(client_id=body['client_id']) def add_product(logic: OrderLogic, order_id: int, product_id: int) -> Order: return logic.add_product(order_id, product_id)

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Response serialization

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Flask + connexion - encoder class ApiJsonEncoder(JSONEncoder):

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Flask + connexion - encoder class ApiJsonEncoder(JSONEncoder): def default(self, obj: Any) -> Any: if isinstance(obj, (datetime.datetime, datetime.date)): return obj.isoformat()

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Flask + connexion - encoder class ApiJsonEncoder(JSONEncoder): def default(self, obj: Any) -> Any: if isinstance(obj, (datetime.datetime, datetime.date)): return obj.isoformat() if isinstance(obj, Client): return {"id": obj.id, "name": obj.name}

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Flask + connexion - encoder class ApiJsonEncoder(JSONEncoder): def default(self, obj: Any) -> Any: if isinstance(obj, (datetime.datetime, datetime.date)): return obj.isoformat() if isinstance(obj, BaseEntity): return {key: value for key, value in vars(obj).items() if value is not None}

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Flask + connexion - encoder class ApiJsonEncoder(JSONEncoder): def default(self, obj: Any) -> Any: if isinstance(obj, (datetime.datetime, datetime.date)): return obj.isoformat() if isinstance(obj, Base): return {key: value for key, value in vars(obj).items() if value is not None} return JSONEncoder.default(self, obj)

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Steps of building the application

  • data definition - entities
  • use cases
  • implement interfaces
  • API
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Clean architecture

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Protect borders

PRO TIP #8

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Borders - project structure

  • shop
  • ram_db
  • api
  • setup.py
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Borders - project structure

  • shop

○ setup.py ○ requirements.txt

  • ram_db

○ setup.py ○ requirements.txt

  • api

○ setup.py ○ requirements.txt

  • setup.py
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Granice - struktura projektu

  • shop

○ setup.py ○ requirements.txt -> injector

  • ram_db

○ setup.py ○ requirements.txt -> shop

  • api

○ setup.py ○ requirements.txt -> shop, ram_db, flask, connexion

  • setup.py
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Borders - project structure

  • shop

○ setup.py ○ requirements.txt

  • ram_db

○ setup.py ○ requirements.txt

  • api

○ setup.py ○ requirements.txt

  • setup.py
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DEMO

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Benefits

  • Business logic independence
  • Ease of technology update/change
  • Clear and secure borders
  • Technology chosen based on knowledge
  • Fast prototyping / POC
  • Ease of testing
  • Installing only required packages
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Architecture is a set of conscious decisions

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Clean architecture is a way to delay important decisions

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Further reading

Clean Architecture - Robert C. Martin https://g.co/kgs/kbaamc Python microlibs: https://medium.com/@jherreras/python-microlibs-5be9461ad979

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Thank you

grzegorz@kocjan.me @GrzegorzKocjan

https://migawka.it/europython2019