Common DDD pitfalls

@ToJans - 2014

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Selling it

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Selling it

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Bounded contexts

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Bounded contexts

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Ignoring bounded contexts

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Ignoring bounded contexts

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Conway’s law

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Conway’s law

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“Gedankenexperiment”

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“Gedankenexperiment”

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Lack of a domain expert

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Lack of a domain expert

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Bounded contexts

A lot Little

POV

Amount

Up- / Downstream A lot Little

Contracts

Dependencies

Some things that work *

* n = 1

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DDD for non-core domains

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DDD for non-core domains

Tactica

l Ignoring some aspects

Tactica

l Ignoring some aspects

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Repositories, exposing state

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Repositories, exposing state

https://www.facebook.com/Jeroom.Inc

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In repos, “Tell, don’t ask”

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In repos, “Tell, don’t ask”

… but don’t overdo it

Infrastructure

Infrastructure

BDUF – what you built

Infrastructure

BDUF – what you need

Infrastructure

Frameworks <> Libraries

Infrastructure

Frameworks <> Libraries

Infrastructure

Frameworks & Libraries: too generic

Infrastructure

Generic frameworks & Libraries => hacks

Infrastructure

Eventual consistency: do you need it?

Infrastructure

Eventual consistency: do you need it?

Infrastructure

Anything: do you need it?

”Il semble que la perfection soit atteinte

non quand il n'y a plus rien à ajouter,

mais quand il n'y a plus rien à retrancher.”

Antoine de Saint-Exupéry

Selling it

Selling DDD to your peers & bosses

Selling it

Tough

Selling it

Really tough

Selling it

This is a different presentation

Selling it

… but I’ll show you the recap

And now it’s time for a

And now it’s time for a

Recap And now it’s time for a

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• Don’t ignore bounded contexts

• Understand Conway’s Law

• Think first, act later

• Have domain experts

Craft BCs and make them explicit

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• Only in core domains

• Find all ways to model them

• Repositories = domain only

• Repositories = Tell, don’t ask

Infrastructure

• Don’t build a BDUF

• Frameworks <> libraries

• Avoid hacks

• Aim for simplicity, not ease of building

Selling it

• Don’t force feed

• Lead by example

• One step at a time

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HAVE FUN!

And now it’s time for

Questions And now it’s time for

What was the background seeded by?

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