Domain Driven Design Handl ing complex bus iness log ic

Can Pekdemi r

12.01.2017

Agenda• Domain Driven Design and the Motivation Behind• Maintaining Model Integrity• Expressing the Model• Lifecycle of Domain Objects

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The Term

• Domain Driven Design: Tackling Complexity in the Heart of Software,

Eric Evans, 2003

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In the Beginning of a Product

Two Major Drawbacks

Growing Complexity

Time to Market

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What is Domain Driven Design?

• An approach to software development for solving complex business problems.

• A mindset of developing business not only software

• A set of patterns, principles and practices

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The Motivation Behind DDD

• Focusing on core domain

• Helping enterprise architecture and organization

• Coping with technology challenges(Enterprise frameworks, NoSQL, Microservices)

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Conway’s Law

“Organizations which design systems are constrained to produce designs which are copies of the communication structures of these organizations.”

— Mel Conway

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Exploring the Domain with Collaboration

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Ubiquitous Language

• One team, one language

• No need for translation

• Use in both communication and in the code

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Analysis and Code Model Separate

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Analysis and Code Model Together

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Hands-on Modelers

• “People who write the code

should feel responsible for the model.”

• “A modeler should not be separated

from implementation.”

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Domain Driven Design Problem SpaceTwo techniques;- Whirlpool- Event Storming

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Big Ball of Mud

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Big Ball of Mud

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Distillation

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Real Numbers• Over 6000 employees• In 400 cities and 70 countries• From 200 engineers to 2000 Engineers only in a year and half• 8000 git repositories• Over 1000 microservices

https://www.youtube.com/watch?v=kb-m2fasdDYWhat I Wish I Had Known Before Scaling Uber to 1000 Services - Matt Ranney“Scaling the traffic is not the issue. Scaling the team and the product feature release rate is the primary driver.”

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Bounded Context• Classical divide-and-conquer strategy

• Divide large system into autonomous contexts

• Be explicit about the context responsibilites

• Each should have a refined model and a ubiquitous language

• Explicitly set boundaries and

relationships with each other

• Care about team organization, code bases, database schemas

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Context Map• Strategic domain driven design• Very useful tool to understand overall architecture and relationships

of the system.

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Preserving Model Integrity

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Isolating the Domain

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Isolation the Domain in Bounded Contexts

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Expressing the Model

• Entities

• Value Objects

• Domain Services

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Entity

• “Many objects are not fundamentally defined by their attributes, but rather by a thread of continuity and identity. ”

• But, Identity is not always an ID.

• Anemic vs. Rich-Behaviour Domain Model

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Value Objects

• Have no conceptual identity, defined by their attributes

• Should be immutable

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Domain Services

• Reflect business processes

• Mainly uses more than one entity or value object

• Should be stateless

• e.g. transferMoney

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Lifecycle of Domain Objects

• Aggregates

• Factories

• Repositories

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Aggregates• Mark one entity as root

• Contains other entities and value objects

• Apply consistency boundaries with aggregates and enforces invariants.

• External objects should not access child entity of Aggregate directly. All access operations should be done over the root

• Beginner for microservices

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Aggregates

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Aggregates

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How to Decide Aggregate Root

• Which entities exist in most operations?

• Cascading delete is okay?

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Factories

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Factory Sample

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Repositories

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Repository - Sample

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Making Implicit Concepts Explicit – Specification Pattern

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Recap• Focus on your domain

• Be explicit about your bounded contexts

• Use context map and be aware of the big picture

• Code should reveal business

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Resources• Books

• Linkshttp://www.clipartkid.com/ubiquitous-language-cliparts/ https://morecoding.wordpress.com/2015/01/03/n-tier-architecture/ https://tommcfarlin.com/wp-content/uploads/2014/08/big-ball-of-mud.jpghttp://howtodoinjava.com/design-patterns/creational/implementing-factory-design-pattern-in-java/

thanks12.01.2017