The document discusses strategies for removing unused attributes from ActiveRecord models in Ruby on Rails. It describes marking attributes as deprecated to prevent direct access and filter them from serialization. This avoids errors on save from missing database columns while allowing existing data to be rendered normally. The process involves marking attributes as deprecated, handling access attempts, updating serialization, and deploying after a migration removes the columns.

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Friday, May 10, 13

2. YANN ARMAND
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@yarmand
Friday, May 10, 13

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The Enterprise Social Network
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4. Friday, May 10, 13

5. DELETE A DB COLUMN
WITHOUT MAKING ZOMBIES
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6. DELETE A DB COLUMN
WITHOUT MAKING ZOMBIES
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7. WHY DELETE A MODEL
ATTRIBUTE ?
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8. WHY DELETE A MODEL
ATTRIBUTE ?
• Not used anymore
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9. WHY DELETE A MODEL
ATTRIBUTE ?
• Not used anymore
User Payment card
• card_type
• card_number
• Move to another model
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10. KILLING AN ACTIVE RECORD
FIELD
Cons
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11. KILLING AN ACTIVE RECORD
FIELD
• Code dependency
Cons
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12. KILLING AN ACTIVE RECORD
FIELD
• Code dependency
Cons
• Unknown impact on the app behavior
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13. KILLING AN ACTIVE RECORD
FIELD
• Code dependency
Cons
• Unknown impact on the app behavior
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14. KILLING AN ACTIVE RECORD
FIELD
• Code dependency
Cons
• Unknown impact on the app behavior
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15. KILL AN ACTIVE RECORD
FIELD
Pros
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16. KILL AN ACTIVE RECORD
FIELD
Pros
• ReduceTechnical Debt
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17. KILL AN ACTIVE RECORD
FIELD
Pros
• ReduceTechnical Debt
• Smaller code base
• Lower barrier of entry
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• Eliminate black holes
• Prevent crashes
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18. BE PREPARED !!
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19. BE PREPARED !!
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20. BE PREPARED !!
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21. class User
deprecate_attribute :card_type
deprecate_attribute :card_number
end
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22. API OUTPUT
render :json => user
name: 'roger'
age: 23
card_type: 'visa'
card_number: 123412341234
name: 'roger'
age: 23
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23. API OUTPUT
render :json => user
name: 'roger'
age: 23
card_type: 'visa'
card_number: 123412341234
name: 'roger'
age: 23
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ActiveRecord#serializable_hash
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24. API OUTPUT
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class User
alias_method :super_serializable_hash, :serializable_hash
def serializable_hash(options = {})
options.merge! {
:only => self.attributes.keys.map(&:to_sym) -
(self.class.deprecated_attributes ||
[]).map(&:to_sym)
}
super_serializable_hash(options)
end
end
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25. API OUTPUT
-
class User
alias_method :super_serializable_hash, :serializable_hash
def serializable_hash(options = {})
options.merge! {
:only => self.attributes.keys.map(&:to_sym) -
(self.class.deprecated_attributes ||
[]).map(&:to_sym)
}
super_serializable_hash(options)
end
end
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26. API OUTPUT
-
class User
alias_method :super_serializable_hash, :serializable_hash
def serializable_hash(options = {})
options.merge! {
:only => self.attributes.keys.map(&:to_sym) -
(self.class.deprecated_attributes ||
[]).map(&:to_sym)
}
super_serializable_hash(options)
end
end
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27. API OUTPUT
-
class User
alias_method :super_serializable_hash, :serializable_hash
def serializable_hash(options = {})
options.merge! {
:only => self.attributes.keys.map(&:to_sym) -
(self.class.deprecated_attributes ||
[]).map(&:to_sym)
}
super_serializable_hash(options)
end
end
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28. ACCESSORS =
[ '',
'=',
'_before_type_cast',
'?',
'_changed?',
'_change',
'_will_change!',
'_was']
Zombie Radar
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FIELD HUNTING
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29. -
def deprecate_attribute attr
msg = "You can't access atribute #{attr}, it has been
deprecated"
ACCESSORS.each do |term|
define_method("#{attr}#{term}") do |*args|
raise DeprecatedAttributeError, msg
super
end
end
end
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30. -
def deprecate_attribute attr
msg = "You can't access atribute #{attr}, it has been
deprecated"
ACCESSORS.each do |term|
define_method("#{attr}#{term}") do |*args|
raise DeprecatedAttributeError, msg
super
end
end
end
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31. -
def deprecate_attribute attr
msg = "You can't access atribute #{attr}, it has been
deprecated"
ACCESSORS.each do |term|
define_method("#{attr}#{term}") do |*args|
raise DeprecatedAttributeError, msg
super
end
end
end
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32. -
def deprecate_attribute attr
msg = "You can't access atribute #{attr}, it has been
deprecated"
ACCESSORS.each do |term|
define_method("#{attr}#{term}") do |*args|
raise DeprecatedAttributeError, msg
super
end
end
end
Friday, May 10, 13

33. -
def deprecate_attribute attr
msg = "You can't access atribute #{attr}, it has been
deprecated"
ACCESSORS.each do |term|
define_method("#{attr}#{term}") do |*args|
raise DeprecatedAttributeError, msg
super
end
end
end
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34. -
def deprecate_attribute attr
msg = "You can't access atribute #{attr}, it has been
deprecated"
ACCESSORS.each do |term|
define_method("#{attr}#{term}") do |*args|
raise DeprecatedAttributeError, msg
super
end
end
end
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35. Friday, May 10, 13

36. class ApplicationController
rescue_from DeprecatedAttributeError, :with => :log_deprecate
private
def log_deprecated e
deprecated_logger.error(e.backtrace.join("n"))
e.continue
end
end
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37. cmaruz/continuable
class ApplicationController
rescue_from DeprecatedAttributeError, :with => :log_deprecate
private
def log_deprecated e
deprecated_logger.error(e.backtrace.join("n"))
e.continue
end
end
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38. REFACTOR
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39. REFACTOR
-
DEPLOY
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40. REFACTOR
New Code
-
DEPLOY
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41. REFACTOR
MigrationNew Code
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DEPLOY
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42. REFACTOR
MigrationNew Code
-
DEPLOY
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43. WHAT HAPPENS ?
name: 'roger'
age: 23
card_type: 'visa'
card_number: 123412341234
-
Time
In Cache
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44. WHAT HAPPENS ?
name: 'roger'
age: 23
card_type: 'visa'
card_number: 123412341234
Deploy
-
Time
In Cache
Friday, May 10, 13

45. WHAT HAPPENS ?
name: 'roger'
age: 23
card_type: 'visa'
card_number: 123412341234
Deploy
name: 'roger'
age: 24
card_type: 'visa'
card_number: 123412341234
-
Time
In Cache Update
Friday, May 10, 13

46. WHAT HAPPENS ?
name: 'roger'
age: 23
card_type: 'visa'
card_number: 123412341234
Deploy
name: 'roger'
age: 24
card_type: 'visa'
card_number: 123412341234
Save
-
Time
In Cache Update
Friday, May 10, 13

47. WHAT HAPPENS ?
name: 'roger'
age: 23
card_type: 'visa'
card_number: 123412341234
Deploy
name: 'roger'
age: 24
card_type: 'visa'
card_number: 123412341234
Save
Database Exception
unknown columns
card_type, card_number
-
Time
In Cache Update
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48. WHAT HAPPENS ?
name: 'roger'
age: 23
card_type: 'visa'
card_number: 123412341234
Deploy
name: 'roger'
age: 24
card_type: 'visa'
card_number: 123412341234
Save
Database Exception
unknown columns
card_type, card_number
-
Time
In Cache Update
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49. IGNORE COLUMNS
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class User
def columns
self.class.columns.reject do |c|
(self.class.deprecated_attributes || []).include? c.name.to_s
end
end
end
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50. THANK YOU !!
https://github.com/yarmand/acread
Acread
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