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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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.slides

section

h2 Domain Driven Design Toolkit

h4

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

h6

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

section

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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section

h2 pros

ol

li.fragment Relatively easy to read

h2.fragment cons

ol

li.fragment Really hard to change

li.fragment We can not see the whole picture

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section

h2 Implicit API

pre

code.python.

class Purchases(viewsets.ModelViewSet):

queryset = Purchase.objects.all()

serializer_class = PurchaseSerializer

permission_classes = (CanPurchase,)

filter_class = PurchaseFilter

pre

code.python.

router.register('/api/purchases/', Purchases)

ol

li.fragment What exactly does this class do?

li.fragment How to use it?

section

h2 pros

ol

li.fragment Relatively easy to change

h2.fragment cons

ol

li.fragment Really hard to read

li.fragment You should keep in mind framework rules

li.fragment Implicit knowledge grow

li.fragment We still can not see the whole picture

section

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.

section

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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section

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

section

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 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.

section

h2

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

p A set of libraries for pluggable business logic components.

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

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section

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

p Define a user story in the business transaction DSL.

p Separate state, implementation and specification.

section

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 Purchase:

@story

@arguments("invoice_id", "user")

def make(I):

I.find_order

I.find_price

I.find_invoice

I.check_balance

I.persist_payment

I.persist_purchase

I.send_purchase_notification

section

h2 Steps implementation

pre

code.python.

from stories import Failure, Success

class Purchase:

# ...

def find_invoice(self, ctx):

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

return Success(invoice=invoice)

def check_balance(self, ctx):

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

return Success()

else:

return Failure()

section

h2 Story Execution

pre

code.python.

>>> Purchase().make(category_id=2)

Purchase.make:

find_order

find_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 Purchase.find_category

section

h2 pros

ol

li.fragment Clean flow in the source code

li.fragment Separate step implementation

li.fragment Each step knows nothing about a neighbor

li.fragment Easy reuse of code

li.fragment Allows to instrument code easily

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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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section

img(src=require("./pics/postgresql.png").default height="150" style=" padding-right: 70px;").plain

img(src=require("./pics/firebase.png").default height="150" style=" padding-right: 70px;").plain

ul

li.fragment We do not have the tooling to work with data

li.fragment There are no data contracts written in code

section

img(src=require("./pics/attrs.png").default).plain

section

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]

section

h2 State Contract

pre

code.python.

from pydantic import BaseModel

class Purchase:

@story

def make(I):

# ...

@Purchase.make.contract

class Context(BaseModel):

user: User

invoice_id: InvoiceId

invoice: Optional[Invoice]

section

h2 pros

ol

li.fragment Explicit data contracts and relations in code

li.fragment Data store independent

li.fragment Catch errors when they occur

li.fragment Not when they propagate to exception

h2.fragment cons

ol

li.fragment Working with data sources manually

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section

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!

section

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": "id"})

@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.aggregates 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}))

section

img(src=require("./pics/pusher.png").default).plain

section

h2 How we use third-party libraries

pre

code.python.

from pusher import Pusher

class Purchase:

def send_purchase_notification(ctx):

Pusher().trigger("private-user-1")

pre

code.python.

def test_before(monkeypatch):

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

# ...

pusher.Pusher.trigger.assert_called_once_with(

"private-user-1"

)

section

img(src=require("./pics/ably.png").default).plain

section

h2 How to use it with DI

pre

code.python.

@dataclass

class Purchase:

def send_purchase_notification(ctx):

self.trigger_message(UserStream(ctx.user))

trigger_message: Emitter

pre

code.python.

def test_after(emitter):

# ...

Purchase.trigger_message.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 Layout

pre

code.

project

├── admin

├── aggregates

├── forms

├── migrations

├── models

├── repositories

├── services

├── templates

├── #[b implementation]

└── views

section

h2 Injection

pre

code.python.

from dependencies import Injector, Package

app = Package('app')

class MakePurchase(Injector):

make_purchase = app.services.Purchase.make

load_category = app.repositories.load_category

load_price = app.repositories.load_price

load_profile = app.repositories.load_profile

MakePurchase.make_purchase(category_id=1, price_id=1)

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h2 Get in touch

ul

li

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

li

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

li

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

li

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