wroc_love.rb 2014 talk on form objects.

1. Objectify Your Forms:
Beyond Basic User Input
DannyOlson
dbolson@gmail.com

2. Corporate Sponsorship
Sharethrough
In-feed advertisingexchange.

3. Background
Forms are common in web applications
Forms often end up savingdatato multiple tables
Rails gives us #accepts_nested_attributes_for
Much magic and potentialconfusion

4. tl;dr
We don'talways have to do things The Rails Way™

5. Ice Cream

6. Memes

7. Online Meme-Based Ice Cream
Ordering Service

8. Class Diagram

9. First Implementation
The Rails Way™

10. classIceCreamsController<ApplicationController
defnew
@ice_cream=IceCream.new
respond_with@ice_cream
end
defcreate
@ice_cream=IceCream.new(valid_params)
if@ice_cream.save
Meme.create_defaults(@ice_cream)
redirect_toedit_ice_cream_path(@ice_cream),
notice:'Icecreamwascreated.'
else
render:new
end
end

11. =form_forice_creamdo|f|
-#otherfieldsomitted
-ifice_cream.persisted?
=f.fields_for:memesdo|fields|
=fields.label:name
=fields.text_field:name
=fields.label:rating
=fields.select:rating,
options_for_select(10.downto(1),fields.object.rating)
-iffields.object.persisted?
=fields.label:_destroy,'Delete'
=fields.check_box:_destroy
=f.submit'MakeItSo(Delicious)'

12. classIceCream<ActiveRecord::Base
accepts_nested_attributes_for:memes,
reject_if:proc{|attr|
attr['name'].blank?||attr['rating'].blank?
},
allow_destroy:true
validates:flavor_id,:serving_size_id,presence:true
validates:scoops,presence:true,inclusion:{in:[1,2,3]}
validate:more_scoops_than_toppings
before_save:set_price
deftopping_ids=(toppings)
filtered_toppings=toppings.reject{|t|!Topping.exists?(t)}
super(filtered_toppings)
end
private
defmore_scoops_than_toppings
ifscoops.to_i<toppings.size
errors.add(:toppings,"can'tbemorethanscoops")
end
end
defset_price
self.price=scoops*100
end

13. Responsibilities
classIceCream<ActiveRecord::Base
reject_if:proc{|attr|
attr['name'].blank?||attr['rating'].blank?
},
allow_destroy:true

14. Responsibilities
classIceCream<ActiveRecord::Base
before_save:set_price
private
defset_price
self.price=scoops*100
end

15. Responsibilities
classIceCream<ActiveRecord::Base
deftopping_ids=(toppings)
filtered_toppings=toppings.reject{|t|!Topping.exists?(t)}
super(filtered_toppings)
end

16. Responsibilities
classIceCream<ActiveRecord::Base
validates:flavor_id,presence:true
validates:serving_size_id,presence:true
validates:scoops,presence:true,inclusion:{in:[1,2,3]}
validate:more_scoops_than_toppings
private
defmore_scoops_than_toppings
ifscoops.to_i<toppings.size
errors.add(:toppings,"can'tbemorethanscoops")
end
end

17. Single Responsibility Principle
Every class should have one, and only one,
reason to change.
1. formatdata
2. save the data
3. check values of associated objects
4. validations

18. Concerning...

19. Early on, SRPis easy to apply. ActiveRecord
classes handle persistence, associations and not
much else. Butbit-by-bit, they grow. Objects
thatare inherently responsible for persistence
become the de facto owner of all business logic
as well. And ayear or two later you have aUser
class with over 500 lines of code, and hundreds
of methods in it’s public interface.
- 7 Patterns to Refactor FatActiveRecord
Models

20. #accepts_nested_attributes_foris
used, in ActiveRecord classes, to reduce the
amountof code in Rails applications needed to
create/update records across multiple tables
with asingle HTTPPOST/PUT. As with many
things Rails, this is convention-driven...
While this sometimes results in less code, itoften
results in brittle code.
- #accepts_nested_attributes_for (Often)
Considered Harmful

21. New Feature Request
We need to base the price off of both
the memes and the amountof scoops.

22. From this:
#app/models/ice_cream.rb
classIceCream<ActiveRecord::Base
defset_price
self.price=scoops*100
end
#app/controllers/ice_creams_controller.rb
classIceCreamsController<ApplicationController
defcreate
@ice_cream=IceCream.new(valid_params)
if@ice_cream.save
Meme.create_defaults(@ice_cream)
redirect_toedit_ice_cream_path(@ice_cream),
notice:'Icecreamwascreated.'
else
render:new
end
end

23. To this:
#app/models/ice_cream.rb
classIceCream<ActiveRecord::Base
defratings_sum
memes.reduce(0){|sum,meme|sum+=meme.rating}
end
defset_price
unlessprice_changed?
self.price=scoops*100
end
end
#app/controllers/ice_creams_controller.rb
classIceCreamsController<ApplicationController
defcreate
@ice_cream=IceCream.new(valid_params)
if@ice_cream.save
Meme.create_defaults(@ice_cream)
meme_ratings=@ice_cream.ratings_sum
@ice_cream.update_attributes!({
price:@ice_cream.price+meme_ratings
})
redirect_toedit_ice_cream_path(@ice_cream),
notice:'Icecreamwascreated.'
else
render:new
end
end

24. There's Another Way

25. Form Object
An objectthatencapsulates context-specific
logic for user input.
Ithas onlythe attributes displayed in the form
Itsets up its own data
Itvalidates thatdata
Itdelegates to persistence butdoesn'tknow specifics

26. Second Implementation
With a Form Object

27. classNewOrderForm
includeVirtus.model
attribute:flavor_id,Integer
attribute:serving_size_id,Integer
attribute:scoops,Integer
attribute:topping_ids,Array[Integer]
end

28. classNewOrderForm
extendActiveModel::Naming
includeActiveModel::Conversion
includeActiveModel::Validations
validates:flavor_id,:serving_size_id,presence:true
validates:scoops,presence:true,inclusion:{in:[1,2,3]}
validate:more_scoops_than_toppings
private
defmore_scoops_than_toppings
ifscoops.to_i<topping_ids.delete_if{|attr|attr==''}.size
errors.add(:topping_ids,"can'tbemorethanscoops")
end
end

29. classNewOrderForm
defsave
ifvalid?
@model=OrderCreating.call(attributes)
true
else
false
end
end
classOrderCreating
defself.call(attributes)
IceCream.transactiondo
ice_cream=IceCream.create!(flavor_id:flavor_id,
serving_size_id:serving_size_id,
topping_ids:topping_ids,
scoops:scoops,
price:scoops*100)
Meme.create_defaults(ice_cream)
ice_cream
end
end
end

30. classEditOrderForm
attribute:memes,Array[EditMemeForm]
classEditMeme
attribute:id,Integer
attribute:name,String
attribute:rating,Integer
attribute:_destroy,Boolean,default:false
validates:name,presence:true
validates:rating,
presence:true,
inclusion:{in:1..10,message:'mustbebetween1and10'}
end

31. classOrdersController<ApplicationController
defnew
@order=NewOrderForm.new
respond_with@order
end
defcreate
@order=NewOrderForm.new(valid_params)
if@order.save
redirect_toedit_order_path(@order),
notice:'Yourorderwascreated.'
else
render:new
end
end
end

32. -iforder.persisted?
-order.memes.each_with_indexdo|meme,index|
-ifmeme.id
=hidden_field_tag"order[memes][][id]",meme.id
=label_tag"order[memes][][name]",'Name'
=text_field_tag"order[memes][][name]",meme.name
=label_tag"order[memes][][rating]",'Rating'
=select_tag"order[memes][][rating]",meme_rating_options
-ifmeme.id
=label_tag"memes_destroy_#{index}"do
=check_box_tag"order[memes][][_destroy]"
Delete

33. classIceCream<ActiveRecord::Base
belongs_to:flavor
belongs_to:serving_size
has_and_belongs_to_many:toppings
has_many:memes,dependent::destroy
end

34. New Feature Request Redux
We need to base the price off of the meme ratings
notjustthe amountof scoops.

35. From this:
classOrderCreating
defself.call(attributes)
IceCream.transactiondo
ice_cream=IceCream.create!(flavor_id:flavor_id,
serving_size_id:serving_size_id,
topping_ids:topping_ids,
scoops:scoops,
price:scoops*100)
Meme.create_defaults(ice_cream)
ice_cream
end
end
end

36. To this:
classOrderCreating
defself.call(attributes)
IceCream.transactiondo
ice_cream=IceCream.create!(flavor_id:flavor_id,
serving_size_id:serving_size_id,
topping_ids:topping_ids,
scoops:scoops,
price:scoops*100)
Meme.create_defaults(ice_cream)
IceCreamPriceUpdating.call(ice_cream)
end
end
end
classIceCreamPriceUpdating
defself.call
meme_ratings=ice_cream.memes.reduce(0){|sum,meme|
sum+=meme.rating
}
ice_cream.update_attributes!(price:ice_cream.price+meme_ratings)
ice_cream
end

37. Benefits
Clearer domain model
Less magic
Simpler to test
Onlyneed to consider the specific context
Easier to maintain and change

38. When to Use a Form Object
A Rule (if you want one):
Use a form object when persisting
multiple ActiveRecord models

39. What's Out There?
redtape gem
activeform-rails gem

41. Thank You

42. Links
dbolson@gmail.com
https://github.com/dbolson/form-object-presentation
https://github.com/solnic/virtus
http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-
activerecord-models
http://evan.tiggerpalace.com/articles/2012/11/07/accepts_nested_attributes_for-
often-considered-harmful/
https://github.com/ClearFit/redtape
https://github.com/GCorbel/activeform-rails