Drive your dba crazy in 3 easy steps

Driving your DBA crazy  in 3 easy steps a scary story by @ziobrando

About meIn the IT ﬁeld since ZX SpectrumGenerally in large scale projects (I might be biased)Freelance consultant: NotOnlyCodeTrainer (Freelance & Skills MaBer + Zenika)Technical WriterBlogger: h?p://ziobrando.blogspot.comTwiBer: ziobrando My e‐mail: alberto.brandolini@gmail.com

@avanscopertawww.avanscoperta.itavanscoperta.wordpress.comalberto.brandolini@avanscoperta.it © Alberto Brandolini 2009

It started small

It grew

It became more and more complex

Somebody’s goBa be  responsible  for that

Useful

but sHll...

When it comes to run a query with 16 joins you’re  the person to call...

When it comes to run a query with 16 joins you’re  the person to call... You can say it  loud, pal

So how do I design a query with 16 joins?

I don’t know

I don’t

I’d rather explore the domain

While Jack works

...in bulk mode, of  course

Type 1 and Type 2

int Type = 1;

int Type = 1; st h is a td oe !!! W h ea n?? lin em

if Germany is Type 6 and Wednesday is type  A then type 1 should  be ...Red

So you’d use a “readable data”, ... are you a communist or a lady?

Analyst Domain Expert Developer DeveloperInterviews Ubiquitous Language Whiteboard discussions Application Code Specs and Test Code documentation © Alberto Brandolini 2011

Analyst Domain Expert Developer DeveloperInterviews Ubiquitous Language Whiteboard discussions SQL Application Code Specs and Test Code documentation DBA © Alberto Brandolini 2011

So You want to speak the Ubiquitous Language, you scumbag? © Alberto Brandolini 2011

So You want to speak the Ubiquitous Language, you scumbag? The only ubiquitous Language is SQL! Every Database speaks it! © Alberto Brandolini 2011

What is a Type 1 you scumbag?!A Type 1 is a Type 1, sir! I can’t hear you!!

What is the complexity  you’re tackling?

Accidental Domain  Complexity Complexity Conventions Behaviour Primary Keys SemanHcs Joins Language Legacy encoding Conceptual integrity Replicas Context BoundaryStored procedures Domain Events Triggers

How much Hme is needed for a newly hired developer to  start being really  producHve?

How many things we need to know before  contribuHng to the  system? 

A new business requirement impacRng  the applicaRon in 20  diﬀerent points is an  architecture problem

unsurprisingly, the more rules you have, the harder it  is to evolve...

You can give your heart to DDD,but your ass belongs to the DB!

Things you don’t share, even with your best friend

Your Toothbrush

Your Comics CollecHon Your Database

Your Harley‐Davidson

The operaHng room

Your Database

THIS DATABASE IS MY DATABASE TRESPASSERS WILL BE SHOT SURVIVORS WILL BE SHOT AGAIN © Alberto Brandolini 2011

Bounded Context‐ Context: a seSng where a word  Shipping appears that determines its  meaning‐ A porRon of the system where the  Ubiquitous language is consistent Payment © Alberto Brandolini ‐ 2010

He’s probably not going to like it © Alberto Brandolini 2011

The inﬁnite workﬂow

add/remove Item Ready for Open ﬁnalize Closed select DeliveryAddress ShippingMode Selection select Shipping Mode Ready for Ready for Shipped ship pay Delivery Payment deliver Delivered return Returned © Alberto Brandolini 2011

Not the same EnHty

Not the same  Aggregate

Aggregate © Alberto Brandolini ‐ 2010

AggregateA group of objects that naturally belong togetherUnit of consistency in the domain modelupdated in the same transacHondeleted togethertransferred together © Alberto Brandolini ‐ 2010

Aggregate <<Entity>> <<Value Object>> Order LineItem date goodsA group of objects that  customer amount quantity notesnaturally belong together ... subtotal() update() ... close()Unit of consistency in the  ship() ...domain model <<Value Object>> <<Value Object>> Money Customer currencyupdated in the same  name amount surname address plus(Money other)transacHon minus(Money other) ...deleted togethertransferred together © Alberto Brandolini ‐ 2010

Customer add/remove Item Ready for addTocart Open ﬁnalize Closed select DeliveryAddress ShippingMode Selection select Shipping Mode Ready for Ready for Shipped ship pay Delivery Payment deliverLogistics Financial Dept Delivered return Returned Customer Care © Alberto Brandolini 2011

Different Domain Experts Different Goals Different Language Different ModelsDifferent Bounded Contexts Different Aggregates © Alberto Brandolini ‐ 2010

And this will lead to...

DuplicaHon

Dont’ Repeat Yourself

“Every piece of knowledge must  have a single, unambiguous,  authorita;ve representa;on  within a system” Andy Hunt ‐ The Pragma;c  Programmer

The duplicaHon dogma

What does YOU mean?

The cost of avoiding duplicaRon increases  with scale

What does within a  system mean?

Consider coupling also

... and by the way, we’re not violaHng the  DRY anyway... :‐)

Data DuplicaHon != behavior duplicaHon

MulHple aggregates Money currency amount plus(Money other) minus(Money other) ... <<Entity>> <<Root>> <<Value Object>> <<Entity>> <<Root>> Order LineItem Customer date goods name customer quantity surname amount notes address ... subtotal() ... update() ... updateDiscount() close() ... ship() ... shipping address <<Value Object>> CustomerData billing address name surname <<Value Object>> Address <<Value Object>> street city country zipcode © Alberto Brandolini ‐ 2010

Tha g at’s g re M ga Y te? ...

Aggregate modeling Hp (from  UDI Dahan): Group words according to the  conversaRons you use them in,  inclute aBributes, not only  classes. Different Stakeholders/Domain Experts will use different  words to fulfill different goals

Events and aggregate coordinaHon ‐ OperaRons spanning mulRple  aggregates shouldn’t be in the same  Unit of Work ‐ CommunicaRon between aggregates  <<Domain Event>> is inherently asynchronous OrderPurchased‐ Domain Events as a communicaRon  order where mechanism when amount ‐ from the outside payment method ‐ among aggregates ... ... © Alberto Brandolini ‐ 2010

Asynchronously responding to events <<Domain Event>> OrderPurchased order where when amount <<Entity>> <<Root>> payment method s u bs <<Entity>> <<Root>> s to ... cri b Order su b s c ri be e s to Customer date ... name customer surname amount address ... ... onPurchaseEvent(...) onPurchaseEvent(...) update() updateDiscount() close() ... ship() ...‐ Don’t forget: Business rules everything!!! © Alberto Brandolini ‐ 2010

The paper‐based systemMany business pre‐date computersTransacHons are oeen NOT a business concernData might be stale... accept itASK the Business

Does it really have to  end like that?

E’ necessario un processo di  sviluppo agile, che permeBa di  raccogliere il feedback di utenH e  Our goal is to establish a creaHve domain experts, in iterazioni brevi. collaboraHon © Alberto Brandolini 2009

Humble Tips:

Personality Rules

Start small

Work Safely

Share the fun

Behave

Thank youalberto.brandolini@avanscoperta.it hBp://ziobrando.blogspot.com twiBer: ziobrando

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Drive your dba crazy in 3 easy steps

by Alberto Brandolini on Oct 12, 2011

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Drive your dba crazy in 3 easy steps Presentation Transcript