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meta(name="description" content="Domain Driven Design Toolkit")

meta(name="author" content="Artem Malyshev")

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title Domain Driven Design Toolkit

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h2 Domain Driven Design Toolkit

h4

a(href="https://github.com/proofit404") Artem Malyshev

h6

a(href="https://twitter.com/proofit404") @proofit404

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h2 BIO

ul

li Co-Founder at #[a(href="https://drylabs.io/") drylabs.io]

li #[a(href="https://dry-python.org/") dry-python.org]

li Django Channels 1.0

li 5 years of experience in Python

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h2 Complexity

p.fragment #[b Accidental complexity] refers to challenges that developers unintentionally make for themselves as a result of trying to solve a problem.

p.fragment #[b Essential complexity] is just the nature of the beast you're trying to tame.

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h2 Accidental complexity

ul

li.fragment AsyncIO vs. Gevent

li.fragment PostgreSQL vs. MongoDB

li.fragment Python vs. Go

li.fragment Emacs vs. Vim

li.fragment Tabs vs. Spaces

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img(src=require("./pics/domain-driven-design.jpg").default).plain

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h2 What is the domain-driven design?

p.fragment Focus on the core complexity and opportunity in the domain

p.fragment Explore models in a collaboration of domain experts and software experts

p.fragment Write software that expresses those models explicitly

p.fragment Speak #[b ubiquitous language] within a #[b bounded context]

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h2 Not about technology

p.fragment You have to master the tool first then you can focus on #[b DDD].

p.fragment In most domain models, most design patterns are technical noise.

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h2 What is a model?

p.fragment #[b HINT:] Not a UML diagram

p.fragment A set of services, entities and value objects expressed in classes, methods, and refs.

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h2

a(href="https://dry-python.org/") dry-python

p A set of libraries for pluggable business logic components.

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p Define a user story in the business transaction DSL.

p Separate state, implementation and specification.

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h2 Layout

pre

code.

project

├── admin

├── forms

├── migrations

├── models

├── #[b services]

├── templates

└── views

section

h2 Specification DSL

pre

code.python.

from stories import story, arguments

class Subscription:

@story

@arguments("invoice_id", "user")

def buy(I):

I.find_order

I.find_price

I.find_invoice

I.check_balance

I.persist_payment

I.persist_subscription

I.send_subscription_notification

section

h2 State Contract

pre

code.python.

from pydantic import BaseModel

class Subscription:

@story

def buy(I):

...

@Subscription.buy.contract

class Context(BaseModel):

user: User

invoice_id: int

invoice: Optional[Invoice]

section

h2 Steps implementation

pre

code.python.

from stories import Failure, Success

class Subscription:

def find_invoice(self, ctx: Context):

invoice = Invoice.objects.get(pk=ctx.invoice_id)

return Success(invoice=invoice)

def check_balance(self, ctx: Context):

if ctx.user.can_pay(ctx.invoice):

return Success()

else:

return Failure()

section

h2 Story Execution

pre

code.python.

>>> Subscription().buy(category_id=2)

Subscription.buy:

find_category

check_price

check_purchase (PromoCode.validate)

find_code (skipped)

check_balance

find_profile

Context:

category_id = 1318 # Story argument

user = #{"<"}User: 3292#{">"} # Story argument

category = #{"<"}Category: 1318#{">"}

# Set by Subscription.find_category

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h2 DEBUG TOOLBAR

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h2(style="color: white") py.test

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h2 Sentry

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h2 ELK

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h2 Layout

pre

code.

project

├── admin

├── #[b aggregates]

├── forms

├── migrations

├── models

├── services

├── templates

└── views

section

h2 dataclasses

pre

code.python.

from dataclasses import dataclass

from typing import List, NewType

OrderId = NewType("OrderId", int)

@dataclass

class LineItem:

product_id: ProductId

@dataclass

class Order:

primary_key: OrderId

items: List[LineItem]

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img(src="https://raw.githubusercontent.com/dry-python/brand/master/logo/mappers.png").plain

p Declarative mappers from ORM models to domain entities. And back again!

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h2 Layout

pre

code.

project

├── admin

├── aggregates

├── forms

├── migrations

├── models

├── #[b repositories]

├── services

├── templates

└── views

section

h2 Django ORM

pre

code.python.

from mappers import Mapper

from app.aggregates import Order, OrderId, User

from app.models import OrderModel, UserModel

mapper = Mapper(Order, OrderModel, {"primary_key": "pk"})

@mapper.reader

def load_order(id: OrderId, user: User) -> Order:

friends = UserModel.objects.filter(

purchases=OuterRef("pk"), friends=user.primary_key)

return OrderModel.objects.filter(pk=id).annotate(

purchased_by_friends=Exists(friends)).get()

section

h2 Swagger definitions

pre

code.python.

from mappers import Mapper

from bravado import swagger_model

from app.aggregates import Price

spec = swagger_model.load_file("price_service.yml")

mapper = Mapper(Price, spec.definitions["Price"])

@mapper.reader

def load_price(id: PriceId) -> Price:

return requests.get(f"http://172.16.1.7/get/{id}")

section

h2 GraphQL queries

pre

code.python.

from mappers import Mapper

from gql import gql, Client, build_schema

from app.models import Invoice

schema = build_schema("invoice_service.graphql")

mapper = Mapper(Invoice, schema.get_type_map()["Invoice"])

@mapper.reader

def load_invoice(id: InvoiceId) -> Invoice:

return Client(schema=schema).execute(gql("""

{

loadInvoice(id: %(id)d)

}

""", {"id": id}))

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h2 Tests & Mocks

pre

code.python.

def test_before(monkeypatch):

monkeypatch.setattr(pusher, "Pusher", Mock())

# ...

pusher.Pusher.trigger.assert_called_once_with(

"private-user-1"

)

def test_after(emitter):

# ...

emitter.trigger.assert_called_once_with(

UserStream(User(primary_key=1))

)

section

img(src="https://raw.githubusercontent.com/dry-python/brand/master/logo/dependencies.png").plain

p Provide composition instead of inheritance.

p Solves top-down approach problem.

section

h2 Dependency Injection

pre

code.python.

from dependencies import Injector, Package

app = Package("project")

class BuySubscription(Injector):

buy_subscription = app.services.Subscription.buy

load_order = app.repositories.load_order

load_price = app.repositories.load_price

load_invoice = app.repositories.load_invoice

BuySubscription.buy_subscription(category_id=1, price_id=1)

section

h2 Refactoring roadmap

ul

li.fragment No DDD at all

li.fragment Stories without contracts

li.fragment Contracts and aggregates

li.fragment Mappers

li.fragment Dependency injection

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h2 Questions?