The document describes 3 easy steps to drive your DBA crazy: 1. Start with a small project that grows increasingly complex without oversight, making someone responsible for the growing complexity. 2. Engage in confusing and nonsensical conversations about the project that frustrate the DBA's attempts to understand it. 3. Repeatedly violate the DBA's authority over and ownership of the database through dangerous or prohibited actions, disrespecting the DBA's expertise.

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

2. About me
In the IT field since ZX Spectrum
Generally in large scale projects (I might be biased)
Freelance consultant: NotOnlyCode
Trainer (Freelance & Skills MaBer + Zenika)
Technical Writer
Blogger: h?p://ziobrando.blogspot.com
TwiBer: ziobrando
My e‐mail:
alberto.brandolini@gmail.com

3. @avanscoperta
www.avanscoperta.it
avanscoperta.wordpress.com
alberto.brandolini@avanscoperta.it
© Alberto Brandolini 2009

4. It started small

5. It grew

6. It became more and more complex

7. Somebody’s goBa be
responsible
for that

11. Useful

12. but sHll...

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

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

16. So how do I design a
query with 16 joins?

17. I don’t know

18. I don’t

19. I’d rather explore the domain

20. While Jack works

22. ...in bulk mode, of
course

24. Type 1 and Type 2

25. int Type = 1;

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

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

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

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

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

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

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

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

34. What is the complexity
you’re tackling?

35. Accidental Domain
Complexity Complexity
Conventions
Behaviour
Primary Keys
SemanHcs
Joins
Language
Legacy encoding
Conceptual integrity
Replicas
Context Boundary
Stored procedures
Domain Events
Triggers

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

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

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

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

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

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

42. Your Toothbrush

43. Your Comics CollecHon
Your Database

44. Your Harley‐Davidson

45. The operaHng room

46. Your Database

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

48. 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

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

50. The infinite workflow

51. 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

52. Not the same EnHty

54. Not the same
Aggregate

55. Aggregate
© Alberto Brandolini ‐ 2010

56. Aggregate
A group of objects that
naturally belong together
Unit of consistency in the
domain model
updated in the same
transacHon
deleted together
transferred together
© Alberto Brandolini ‐ 2010

57. Aggregate
<<Entity>> <<Value Object>>
Order LineItem
date goods
A group of objects that customer
amount
quantity
notes
naturally belong together
...
subtotal()
update() ...
close()
Unit of consistency in the ship()
...
domain model <<Value Object>>
<<Value Object>>
Money
Customer
currency
updated in the same
name amount
surname
address plus(Money other)
transacHon
minus(Money other)
...
deleted together
transferred together
© Alberto Brandolini ‐ 2010

58. 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
deliver
Logistics
Financial
Dept
Delivered return Returned
Customer
Care © Alberto Brandolini 2011

59. Different Domain Experts
Different Goals
Different Language
Different Models
Different Bounded Contexts
Different Aggregates
© Alberto Brandolini ‐ 2010

60. And this will lead to...

61. DuplicaHon

62. Dont’
Repeat
Yourself

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

64. The duplicaHon dogma

65. What does YOU mean?

66. The cost of avoiding
duplicaRon increases
with scale

67. What does within a
system mean?

68. Consider coupling also

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

70. Data DuplicaHon !=
behavior duplicaHon

71. 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

72. Th
a g at’s
g re M
ga Y
te?
...

73. 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

74. 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

75. 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

76. The paper‐based system
Many business pre‐date computers
TransacHons are oeen NOT a
business concern
Data might be stale... accept it
ASK the Business

77. ! Single source of truth?
© Alberto Brandolini ‐ 2010

78. ! Single source of truth?
‐ Once it used be paper...
© Alberto Brandolini ‐ 2010

79. ! Single source of truth?
‐Once it used be paper...
‐ now the best candidate is Events
© Alberto Brandolini ‐ 2010

80. That’s gonna make him REALLY angry
© Alberto Brandolini 2011

81. © Alberto Brandolini 2011

82. © Alberto Brandolini 2011

83. Does it really have to
end like that?

84. 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

85. We did it with the worst Domain
Experts... can’t we do it with the DBA?
© Alberto Brandolini 2009

86. We did it with the worst Domain
Experts... can’t we do it with the DBA?
© Alberto Brandolini 2009

87. Humble Tips:

88. Personality Rules

89. Start small

90. Work Safely

91. Share the fun

92. Behave

94. Thank you
alberto.brandolini@avanscoperta.it
hBp://ziobrando.blogspot.com
twiBer: ziobrando