This document discusses some of the issues with overusing ActiveRecord in Ruby on Rails applications. It notes that ActiveRecord can promote poor abstraction and "leaky" abstractions as developers are tempted to put too much logic directly in the database layer. The document recommends following principles like the Law of Demeter to avoid excessive "connascence", keeping database queries efficient by using includes, and preferring domain-specific methods over long chains of calls. Overall it argues that while ActiveRecord can be convenient, developers should be mindful not to let it dictate their application's design.

1. ActiveRecord
is Rotting Your Brain
@ethangunderson
Great Lakes Ruby Bash 2011

2. Order.all.select{ |order| order.status == ‘open’ }
Order.all.slice(0, N).map(&:id)

3. Abstractions

4. “All non-trivial
abstractions, to
some degree, are
leaky.”
- Joel Spolsky

5. The Law of Leaky
Abstractions

6. Order.all.select{ |order| order.status == ‘open’ }

7. SELECT * FROM orders;
Typecast each record returned
into an ActiveRecord Order
object.

8. Order.all.select{ |order| order.status == ‘open’ }

9. class Order < ActiveRecord::Base
named_scope :open,
where(:status => ‘open’)
end
Orders.open
Order.where(:status => ‘open’)

10. SELECT * FROM orders where status =
‘open’;

11. validates_uniqueness_of

12. User 1: Checks
for uniqueness
User 2: Checks
for uniqueness
User 1: Inserts
record
User 2: Inserts record

13. Solution
Create a Unique Index

14. Law of Demeter

15. Each unit should have only limited
knowledge about other units: only
units "closely" related to the current
unit.
Each unit should only talk to its
friends; don't talk to strangers.
Only talk to your immediate friends.

16. order.user.address.stree
t

17. class Order < ActiveRecord::Base
belongs_to :user
delegate :street, :to => :user
end
class User < ActiveRecord::Base
has_one :address
delegate :street, :to => :address
end

18. class Order < ActiveRecord::Base
belongs_to :user
def address_street
user.address_street
end
end
class User < ActiveRecord::Base
has_one :address
def address_street
address.street
end
end

19. N+1
users = User.all
users.each do |user|
user.address.street
end

20. 1
users = User.includes(:address).all
users.each do |user|
user.address.street
end

21. N*OMG
orders = Order.all
orders.each do |order|
order.item.name
order.user.address.street
order.item.merchant.name
*
end

22. orders = Order.includes(:user
=> :address).all
orders.each do |order|
order.item.name
order.user.address.street
order.item.merchant.name
*
end

23. ActiveRecord
All Over The Place

24. Connascence

25. Connascence of Name
Connascence of Type
Connascence of Meaning
Connascence of Position
Connascence of
Algorithm
Connascence of
Execution
Connascence of Timing
Connascence of Identity

26. Rule of Degree
Connascence of Name
Connascence of Type
Connascence of Meaning
Connascence of Position
Connascence of Algorithm
Connascence of Execution
Connascence of Timing
Connascence of Identity

27. order.update_attributes({
:status => ‘closed’
})

28. order.close!

29. Connascence of
Meaning
Connascence of Name

30. user = User.find(params[:user_id])
user.orders.create(params[:order])

31. user = User.find(params[:user_id])
user.add_order(params[:order])

32. current_user.orders.open.order(:created_a
t)

33. current_user.current_orders

34. The Database
is
Your Friend

35. github.com/trptcolin/consistency_fail

36. In your ~/.irbrc...
if Object.const_defined?('ActiveRecord')
ActiveRecord::Base.logger =
Logger.new(STDOUT)
end

37. https://github.com/dsboulder/
query_reviewer

38. Thanks!

39. Hiring