DDD Dirty Harry style

Dirty
Harry’s
Style
@ziobrando
DDD
giovedì 23 maggio 13

Goal #1
Domain-Driven
Design NOT
starting from
scratch

Goal #2
Arrive to DDD in a
non prescriptive
fashion

Do you really need me?

Checkpoint
When to apply DDD?
- Complex problem
- High expectations

Anti-pattern
I want to do DDD
I don’t know DDD well...
...so I apply DDD to a
simple problem
I don’t see any advantage
...DDD is useless.

We don’t learn in flatlandsgiovedì 23 maggio 13

That’s not our job

Call a Bomb Squad

Our Safety Net
✓Environments
✓Build Scripts
✓Test suite
✓Private Database
✓Fixtures
✓Continuous
Integration
✓...

Professionals

Proper Tools

Even in the worst situations

Could

you
please
pass
me

the
...thing?
The
s5ngy
one?
Yes,

the
one
that
looks

like
...
that

Precision

Contraceptive
Aspirin

Language

avanscoperta
Checklist
Tools? --> Tool. (always the same)
Precision? --> “When you are in state 12,
the ﬁeld MRKT_NFLD can be only B or
K”
Language? --> :-(

Application

Application
Application

Application
ApplicationApplication

Application
Application

Application
Application
Application

Application
Application
Application
Database

Application
Application
Application
Database
Application

Application
Application
Application
Database
Application
Application

Application
Application
Application
Database
Application
Application
Database

Application
Application
Application
Database
Application
Application
Database
Data-based integration

avanscoperta
Data-‐based
integra5on
checklist
Can we tell...
Which application is responsible for the data
structure?
Which requirement inﬂuenced data deﬁnition?
Is it still valid?
It it valid in my context?
Which applications use that data?
Which consequences if we alter the structure?

Goal #1
Arrive to DDD in a
brownfield
scenario

Solution #1
Put the mess
aside and start
form a greenfield
scenario

Which problem
do we want to
solve?

Our
problem

85%
15%
Our PROBLEM domain
past SOLUTIONS
Complexity

Our problem
Il nostro contesto
I nostri dati
I dati dacondividere
Altro contesto
Altro contesto
Il nostro database
Language!!

TRESPASSERS
WILL BE SHOT
SURVIVORS WILL
BE SHOT AGAIN
THIS DATABASE IS
MY DATABASE

“Put
in
this
way,
it’s

simple...”
Dev:

DDD helps to
solve complex
problems,

DDD helps to
solve complex
problems,
NOT to make
simple problems
complicated

Zombie
management
strategies

A fence...

Learnt from the Romans

Romulus,
let
me

run
this
query,

please...

Romulus,
let
me

run
this
query,

please...
Nope.

Romulus,
let
me

run
this
query,

please...
Nope.
Please,

Romulus
...
it’s
a

read-‐only
one

Bounded
Context

Anti-Corruption Layer
getContattiUnici(…):List<Contatto>
<<Service>>
ContactService
ContactService
context boundary
Attributo
Attributo
<<Value Object>>
Contatto
Attributo
Attributo
<<Entity>>
MyEntity
Our Context ACL
context boundary
Componente
Other Context

<<Service>>
ContactService
ContactService
context boundary
Attributo
Attributo
<<Value Object>>
Contatto
Attributo
Attributo
<<Entity>>
MyEntity
Our Context ACL
context boundary
Componente
Other Context
Model as it
should be

<<Service>>
ContactService
ContactService
context boundary
Attributo
Attributo
<<Value Object>>
Contatto
Attributo
Attributo
<<Entity>>
MyEntity
Our Context ACL
context boundary
Componente
Other Context
Model as it
should be
The legacy
component
with all its
troubles

<<Service>>
ContactService
ContactService
context boundary
Attributo
Attributo
<<Value Object>>
Contatto
Attributo
Attributo
<<Entity>>
MyEntity
Our Context ACL
context boundary
Componente
Other Context
Model as it
should be
The legacy
component
with all its
troubles
Here we solve the
mess, by any
possible means.

...and within our
Bounded Context...

The ideal model

It’s not that
important...

Compliance

There’s no
medal

But maybe...
http://www.youtube.com/watch?v=zDZFcDGpL4U

DDD as a
learning
process

DDD patterns
support
frequent
rewritings

DDD as an
architecture that
supports
evolution

...better provide us
the right support
tool for design

Whiteboards

CRC Cards

“Can
we
really
do

this?”
P.O.:

“We
need
to
put
a

valida9on
layer
to

avoid
incorrect
data

to
enter
into
the

system”
Dev:

Complex
validation is a
smell

(almost) same data
Different Behaviour
submit
registerPayment
amount
customer
state
<<Entity>>
Fattura
edit
validate
amount
customer
<<Entity>>
InvoicePreview

Multiple models

Frequent
Archetypes

3 archetypes?
Collaborative construction
Topic+Conversation
Facebook, Basecamp, Github
Execution
State machines, Commands
Tracking
Logging, Auditing, Datawarehouse, Events

Haven’t put “why do all my DDD
application looks the same” online, yet

What does the
DBA say?

“I
was
expec9nd
the

DB
structure
to
be

deﬁned
once
for

all...”
DBA:

My first idea...

She doesn’t exist in
reality

Can a software
component designed
before one application
be adequate to N
following applications?

Obstaclesgiovedì 23 maggio 13

You have to
watch your back
before interacting
with system X

There are some
f***ing stored
procedures that run
every 10 minutes

Nobody knows
exactly how do
they work

Nobody knows
exactly how do
they work
Nobody ever
changed them and
came back alive

Dress
up

properly
before
going

out!
Are
you

wearing
your
T-‐
shirt?Lock
the
door
when

you
get
out!
Drive
slowly!

Cognitive load
How many
things should
I know, before
touching the
code?

can we be
ignorant and
productive at the
same time?

Transaction management?
Presentation Layer Application Layer Domain Layer Infrastructure
Layer
DDD
99%
ofexamplesgiovedì 23 maggio 13

Repository & SRP
delivery()
price
customer
<<Entity>>
Order
createOrder(…)
delivery(order_ID, …)
<<Facade>>
Application Facade
+saveChanges()
<<ORM>>
Context
save(Order, Context)
findById(id, Context)
<<Repository>>
OrderRepository
createEmpty()
<<factory>>
OrderFactory
opens / closes
uses
creates
Infrastructure layer
Application Layer
Domain Layer
Riceve il contesto
transazionale
dall'esternoIl Repository effettua le
operazioni di aggiunta e/o
rimozione dal contesto, ma è
l'application layer ad invocare
saveChanges()
Crea il
contesto e lo
passa al
repository

Do not
accept
candies
from
strangers

...why don’t we
set up a shared
database table?...

Ooops...

Do not accept
candies

Motivations

Difficult childhood
name
surname
phoneNumber
Person
studentCardNumber
Student
subject
status
Professor

Show me
you’re a
person...

...print
yourself!

Difficult Childhood
name
surname
phoneNumber
Person
studentCardNumber
Student
subject
status
Professor

The two things do not match
...and it’s not an ORM problem

Every
architectural rule
that starts with
“every” is wrong

Consequences

You see,the worls is
divided into two
categories: the one in a
Bounded Context,and
the one who digs...

You ...dig!

Estimations

The tile layer

Accounting it right

Accounting it right
Implementing amazing
functionalities € 10.000

Accounting it right
Learning new techniques
and tools € 4.000

Accounting it right
and tools € 4.000
Establish Safety Conditions € 12.000

Accounting it right
and tools € 4.000
Establish Safety Conditions € 12.000
Cleaning up somebody else’s
mess € 8.000

That
will
cost
you

an
€xtra,
sir...

Value
Don’t forget to
count the extra
value also.

Estimations
“Explorative” evolutions

Estimations
“Explorative” evolutions
Legacy “Pandora’s box”

Ignorance based planning
100%
0
10%
20%
30%
40%
50%
60%
70%
80%
90%
Ignorance
Ignorance
BreakthroughIgnorance

Gold plating?

Product

Owner
Team

Product

Owner
Team
A
simple
requirement

Product

Owner
Team
A
simple
requirement A
simple
requirement

Product

Owner
Team
A
simple
requirement A
simple
requirement
Done
as
DDD
prescribes

Product

Owner
Team
A
simple
requirement A
simple
requirement
Done
as
DDD
prescribes
In
a
clean
and
elegant

fashion

Product

Owner
Team
A
simple
requirement A
simple
requirement
Done
as
DDD
prescribes
In
a
clean
and
elegant

fashion
Soon

Product

Owner
Team
A
simple
requirement A
simple
requirement
Done
as
DDD
prescribes
In
a
clean
and
elegant

fashion
Soon ....ooops

Yes, but how can I
understand if I am
doing DDD?

avanscoperta
Are
we
really
doing
DDD?
Result is better than expectations
No fear in rewriting pieces
We’re having fun

Questions?

Questions?
Really, you can...

Thank you
@ziobrando
alberto.brandolini@avanscoperta.it

DDD Dirty Harry style

Recommended

Recommended

More Related Content

What's hot

What's hot (7)

Viewers also liked

Viewers also liked (20)

Similar to DDD Dirty Harry style

Similar to DDD Dirty Harry style (9)

More from Alberto Brandolini

More from Alberto Brandolini (20)

Recently uploaded

Recently uploaded (9)

DDD Dirty Harry style