Interacting directly with a datastore can have many pitfalls. The presentation goes through an example which exposes some of the pitfalls, then shows how Ohm helps to solve them or make them a non issue. Some basic features of Ohm also covered.

1. Ohm
Object hash map Christopher Spring

2. A little
background
info first...

3. Ohm runs on redis

4. Ohm runs on redis
Remote dictionary server

5. Ohm runs on redis
Remote dictionary server
Store multiple data-structure types

6. Ohm runs on redis
Remote dictionary server
Store multiple data-structure types
Lists, Sets, Sorted Sets, Strings, Hashes

7. Ohm runs on redis
Remote dictionary server
Store multiple data-structure types
Lists, Sets, Sorted Sets, Strings, Hashes
In memory datastore with persistence strategies

8. Ohm runs on redis
Remote dictionary server
Store multiple data-structure types
Lists, Sets, Sorted Sets, Strings, Hashes
In memory datastore with persistence strategies
Super fast & easy to scale

9. Ohm runs on redis
Remote dictionary server
Store multiple data-structure types
Lists, Sets, Sorted Sets, Strings, Hashes
In memory datastore with persistence strategies
Super fast & easy to scale
Atomic operations & transactions

10. Ohm runs on redis
Remote dictionary server
Store multiple data-structure types
Lists, Sets, Sorted Sets, Strings, Hashes
In memory datastore with persistence strategies
Super fast & easy to scale
Atomic operations & transactions
Key expiry

11. Ohm runs on redis
Remote dictionary server
Store multiple data-structure types
Lists, Sets, Sorted Sets, Strings, Hashes
In memory datastore with persistence strategies
Super fast & easy to scale
Atomic operations & transactions
Key expiry
redis-rb

12. What is Ohm?

14. Ancient syllable

15. Ancient syllable
Aaa-ooo-mmm

16. Ancient syllable
Aaa-ooo-mmm
The beginning, duration and
dissolution of the universe

17. Ancient syllable
Aaa-ooo-mmm
The beginning, duration and
dissolution of the universe
Brahma, Vishnu & Shiva

18. or...

19. symbol = {
:name => 'Ohm',
:description => 'Ancient syllable',
:phonemes => [
{
:sound => 'aaa',
:meaning => 'beginning of the universe',
:god => 'Brahma'
}, {
:sound => 'ooo',
:meaning => 'duration of the universe',
:god => 'Vishnu'
}, {
:sound => 'mmm',
:meaning => 'dissolution of the universe',
:god => 'Shiva'
}
]
}

20. Let’s store that in
redis...

21. require 'redis'
db = Redis.new

22. # make a bunch of phonemes
# HMSET key field value [field value ...]
phos = %w(pho1 pho2 pho3)
db.hmset phos[1], 'sound', 'aaa',
'meaning', 'beginning',
'god', 'Brahma'
db.hmset phos[2], 'sound', 'ooo',
'meaning', 'duration',
'god', 'Vishnu'
db.hmset phos[3], 'sound', 'mmm',
'meaning', 'dissolution',
'god', 'Shiva'

23. # ... and create the symbol
db.hmset 'symbol',
'name', 'Ohm'
'description', 'Ancient syllable',
'phonemes', phos.to_json

24. require 'redis'
db = Redis.new
phos = %w(pho1 pho2 pho3)
db.hmset phos[1], 'sound', 'aaa', 'meaning', 'beginning',
'god', 'Brahma'
db.hmset phos[2], 'sound', 'ooo', 'meaning', 'duration',
'god', 'Vishnu'
db.hmset phos[3], 'sound', 'mmm', 'meaning', 'dissolution',
'god', 'Shiva'
db.hmset 'symbol',
'name', 'Ohm'
'description', 'Ancient syllable',
'alternatives', 'alternatives',
'phenomes', phos.to_json

25. Awesome?

26. I want lot’s of Symbols

27. I want lot’s of Symbols
db.hmset 'symbol',
'name', 'Ohm'
'description', 'Ancient syllable',
'alternatives', 'alternatives',
'phenomes', phos.to_json

28. I want lot’s of Symbols

29. I want lot’s of Symbols

30. I want lot’s of Symbols
Require a key strategy

31. I want lot’s of Symbols
Require a key strategy
Store the key in redis

32. I want lot’s of Symbols
Require a key strategy
Store the key in redis
Auto-increment

33. # "symbol:1", "symbol:2" ... "symbol:n"
def get_symbol_pk
pk = db.incr 'symbol:pk'
"symbol:#{pk}"
end
# ...
db.hmset get_symbol_pk, ...

34. Ok, but...

35. I wanna find symbols by
name!

36. I wanna find symbols by
name!
Requires an extra index

37. I wanna find symbols by
name!
Requires an extra index
Store index in a hash or a set

38. I wanna find symbols by
name!
Requires an extra index
Store index in a hash or a set
We need an index key strategy

39. I wanna find symbols by
name!
Requires an extra index
Store index in a hash or a set
We need an index key strategy
...

40. SYMBOL_NAME_INDEX = 'symbol:index:name'
def store_name_index symbol_key, name
db.sadd "#{SYMBOL_NAME_INDEX}:#{name}", symbol_key
end
def find_symbol_by_name name
db.get "#{SYMBOL_NAME_INDEX}:#{name}"
end
# Transaction...
db.multi do
symbol_key = get_symbol_pk
db.hmset get_symbol_pk,
'name', symbol_name,
...
store_name_index symbol_key, symbol_name
end

41. SYMBOL_NAME_INDEX = 'symbol:index:name'
def store_name_index symbol_key, name
db.sadd "#{SYMBOL_NAME_INDEX}:#{name}", symbol_key
end
def find_symbol_by_name name
db.get "#{SYMBOL_NAME_INDEX}:#{name}"
end
# Transaction...
db.multi do
symbol_key = get_symbol_pk
db.hmset get_symbol_pk,
'name', symbol_name,
...
store_name_index symbol_key, symbol_name
end

42. SYMBOL_NAME_INDEX = 'symbol:index:name'
def store_name_index symbol_key, name
db.sadd "#{SYMBOL_NAME_INDEX}:#{name}", symbol_key
end
def find_symbol_by_name name
db.get "#{SYMBOL_NAME_INDEX}:#{name}"
end
# Transaction...
db.multi do
symbol_key = get_symbol_pk
db.hmset get_symbol_pk,
'name', symbol_name,
...
store_name_index symbol_key, symbol_name
end

43. Fine, but now i want...

44. Fine, but now i want...
Validation

45. Fine, but now i want...
Validation
To use this in project X

46. Fine, but now i want...
Validation
To use this in project X
To be able to find the symbol of a phoneme

47. Fine, but now i want...
Validation
To use this in project X
To be able to find the symbol of a phoneme
... shoot me?

48. This sucks!!
Not OO at all
Validation?
Referencing containing object
What other pitfalls have we missed?
Project/implementation specific
...

49. Let’s build our own object
mapping on top of redis!

50. or...

51. Ohm: Object hash map

52. symbol = {
:name => 'Ohm',
:description => 'Ancient syllable',
:phonemes => [
{
:sound => 'aaa',
:meaning => 'beginning of the universe',
:god => 'Brahma'
}, {
:sound => 'ooo',
:meaning => 'duration of the universe',
:god => 'Vishnu'
}, {
:sound => 'mmm',
:meaning => 'dissolution of the universe',
:god => 'Shiva'
}
]
}

53. require 'rubygems'
require 'ohm'
class AncientSymbol < Ohm::Model
attribute :name
attribute :description
index :name
collection :phonemes, Phoneme
def validate
assert_present :name
end
end

54. class Phoneme < Ohm::Model
attribute :sound
attribute :meaning
attribute :god
index :sound
index :god
reference :ancient_symbol, AncientSymbol
def validate
assert_present :sound
end
end

55. Ohm.connect
symbol = AncientSymbol.create
p symbol.valid? # false
p symbol.errors # [[:name, :not_present]]

56. error_messages = symbol.errors.present do |e|
e.on [:name, :not_present] do
"Symbols must have a name."
end
end

57. symbol = AncientSymbol.new :name => 'Ohm'
if symbol.save
symbol.phonemes << Phoneme.create(
:sound => 'aaa',
:meaning => 'beginnging of universe',
:god => 'Brahma',
:ancient_symbol => symbol )
# ...
end

58. Cool, so how do find stuff?

60. Phoneme.all

61. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>

62. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'

63. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>

64. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'

65. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'
# <Set (Phoneme): ["1"]>

66. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'
# <Set (Phoneme): ["1"]>
pho = Phoneme[1]

67. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'
# <Set (Phoneme): ["1"]>
pho = Phoneme[1]
# <Phoneme:1 ancient_symbol_id="1" sound="aaa"

68. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'
# <Set (Phoneme): ["1"]>
pho = Phoneme[1]
# <Phoneme:1 ancient_symbol_id="1" sound="aaa"
meaning="beginnging of universe" god="Brahma">

69. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'
# <Set (Phoneme): ["1"]>
pho = Phoneme[1]
# <Phoneme:1 ancient_symbol_id="1" sound="aaa"
meaning="beginnging of universe" god="Brahma">
pho.ancient_symbol

70. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'
# <Set (Phoneme): ["1"]>
pho = Phoneme[1]
# <Phoneme:1 ancient_symbol_id="1" sound="aaa"
meaning="beginnging of universe" god="Brahma">
pho.ancient_symbol
# <AncientSymbol:1 name="Ohm" description=nil>

71. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'
# <Set (Phoneme): ["1"]>
pho = Phoneme[1]
# <Phoneme:1 ancient_symbol_id="1" sound="aaa"
meaning="beginnging of universe" god="Brahma">
pho.ancient_symbol
# <AncientSymbol:1 name="Ohm" description=nil>
symbol.phonemes

72. Phoneme.all
# <Set (Phoneme): ["3", "1", "2"]>
Phoneme.all.except :sound => 'ooo'
# <Set (Phoneme): ["3", "1"]>
Phoneme.find :sound => 'aaa'
# <Set (Phoneme): ["1"]>
pho = Phoneme[1]
# <Phoneme:1 ancient_symbol_id="1" sound="aaa"
meaning="beginnging of universe" god="Brahma">
pho.ancient_symbol
# <AncientSymbol:1 name="Ohm" description=nil>
symbol.phonemes
# <Set (Phoneme): ["3", "1", "2"]>

73. We also get sorting...

75. symbol.phonemes.sort
# [<Phoneme:1>, <Phoneme:2>, <Phoneme:3>]

76. symbol.phonemes.sort
# [<Phoneme:1>, <Phoneme:2>, <Phoneme:3>]
symbol.phonemes.sort_by( :sound, :order => 'ALPHA DESC' )
# [<Phoneme:2>, <Phoneme:3>, <Phoneme:1>]

77. symbol.phonemes.sort
# [<Phoneme:1>, <Phoneme:2>, <Phoneme:3>]
symbol.phonemes.sort_by( :sound, :order => 'ALPHA DESC' )
# [<Phoneme:2>, <Phoneme:3>, <Phoneme:1>]
symbol.phonemes.sort_by( :sound, :get => :god )
# ["Shiva", "Brahma", "Vishnu"]

78. What else can we do?

79. Attribute types
attribute
set
list
counter
reference
collection

80. Available validation
assert_present
assert_format
assert_numeric
assert_unique

81. ohm-contrib
Boundaries
Callbacks
Timestamping
ToHash
WebValidations
NumberValidations
ExtraValidations
Typecast
Locking

82. Awesome?

83. Questions?

84. Links
www.christopherspring.com
http://ohm.keyvalue.org/
http://www.redis.io/