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HELLO!
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I’m Piotr Solnica :)
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No content
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No content
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Ruby developer
github.com/solnic
@_solnic_
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powow.no
gitorious.org
evofitness.no
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Convenience
vs
Simplicity
Piotr Solnica / RedDotRubyConf / Singapore 2014
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Convenience
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www.oxforddictionaries.com/definition/english/convenience
“The state of being able to proceed with
something without difficulty”
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Look at all the things
I’M NOT doing!
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Simplicity
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www.oxforddictionaries.com/definition/english/simplicity
“The quality or condition of being easy to
understand or do”
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Separation
of
Concerns
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# simple!
class User < ActiveRecord::Base
# all the things we’re not doing
end
!
# still very simple!
user = User.find_by(name: "Jade")
user.mutate_it_somehow
user.save
# again simple!
User.create(params[:user])
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It’s all so simple,
right?
:)
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No content
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It is all
CONVENIENT
(but not simple)
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User.create(params[:user])
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• Input data coercion
• Setting default values
• Input data validation
• Interaction with the database
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• Business logic hidden in life-cycle hooks
• Handling nested-data structures (via
accepts_nested_attributes_for)
• Data normalization through custom attribute
writers
• …
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Separation
of
Concerns
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tuple = params_processor.call(params[:user])
errors = validator.call(tuple)
repository.insert(tuple) if errors.empty?
input data coercion
data validation
persistence
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def create(params)
tuple = params_processor.call(params[:user])
errors = validator.call(tuple)
repository.insert(tuple) if errors.empty?
end
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Data & Behavior
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# CONVENIENCE
!
class User < ActiveRecord::Base
!
def full_name
"#{first_name} #{last_name}"
end
!
end
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# SIMPLICITY
!
!
data = {
first_name: "Jade",
last_name: "Doe",
email: "[email protected]"
}
class Presenter
def initialize(data)
@data = data
end
def full_name
"#{@data[:first_name]} #{@data[:last_name]}"
end
end
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Presenter.new(data).full_name
=> "Jade Doe"
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Convenience
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Simplicity
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Focus on what’s essential
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Try to be minimalistic
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Immutability
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presenter = Presenter.new(data)
data[:first_name].upcase!
presenter.full_name
# JADE Doe
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Oh You Mutable State!
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require "ice_nine"
IceNine.deep_freeze(data)
presenter = Presenter.new(data)
data[:first_name].upcase!
# BOOM! RuntimeError: can't modify frozen String
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Adamantium
github.com/dkubb/adamantium
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class Money
include Adamantium
attr_reader :value, :currency
def initialize(data)
@value, @currency = data.values_at(:value, :currency)
end
end
money = Money.new(value: 123.12, currency: "pln")
money.currency.upcase!
# BOOM! RuntimeError: can't modify frozen String
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Relational Model
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“Out of the Tar Pit” Ben Moseley, Peter Marks
“The relational model has — despite its origins
— nothing intrinsically to do with databases.
Rather it is an elegant approach to structuring
data, a means for manipulating such data, and
a mechanism for maintaining integrity and
consistency of state”
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Structure
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require "axiom"
users = Axiom::Relation.new([
[:user_id, Integer],
[:name, String]
])
!
tasks = Axiom::Relation.new([
[:user_id, Integer],
[:title, String]
])
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Manipulation
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users = users.insert([[1, "Jade"]])
tasks = tasks.insert([[1, "Task One”]])
users_tasks = proc { |user_id|
users.
join(tasks).
rename(name: :user_name).
restrict(user_id: user_id).
project([:user_name, :title])
}
users_tasks.call(1).to_a
# [{:user_name=>"Jade", :title=>"Task One"}]
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users.join(tasks).insert([[1, "Jade", "Jade's Task"]]).to_a
# => [{:user_id=>1, :name=>"Jade", :title=>"Jade's Task"}]
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“Data Independence - a clear separation is
enforced between the logical data and its
physical representation”
“Out of the Tar Pit” Ben Moseley, Peter Marks
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Relations as
1st class citizens
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class User < ActiveRecord::Base
def self.active
where(active: true)
end
end
# returns a relation with *all the data*
User.all
# returns a relation with *a subset* of all the data
User.active
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Let’s put relations in front
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class RelationRegistry
def initialize
@registry = {}
# internal base relation, not exposed to the outside world
@registry[:users] = Axiom::Relation.new(
[[:name, String], [:active, Boolean]]
)
end
# derived, public relation with active users
def active_users
@registry[:users].restrict(active: true)
end
end
relations = RelationRegistry.new
relations.active_users
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Composability
&
Encapsulation
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# Find all users without tasks
# we need to resort to a hand-written partial SQL
User.
joins(
"left outer join tasks on tasks.user_id = users.user_id”
).
where(tasks: { id: nil })
# won't work as it produces an inner join
User.joins(:tasks).where(:tasks => { :id => nil })
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Composing queries
gives very little confidence
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Rather than composing
queries, let’s compose relations
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# Find all users without tasks
users_with_tasks = users.join(tasks).project([:user_id, :name])
# difference relational operator
users_with_no_tasks = users.difference(users_with_tasks)
# ...or just
users_with_no_tasks = users - users_with_tasks
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Ruby Object Mapper
github.com/rom-rb
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Relations (aka data)
Mapping to objects
Simplicity
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Logical Schema
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rom = ROM::Environment.setup(:memory)
rom.schema do
!
relation(:users, internal: true) do
attribute :id, Integer, rename: :user_id
attribute :name, String
key :user_id
end
relation(:tasks) do
attribute :user_id, Integer
attribute :title, String
key :user_id, :title
end
!
end
that’s a base, internal
relation
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Public “external” relations
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rom.schema do
!
relation(:users_tasks) do |user_id|
users.
join(tasks).
rename(name: :user_name).
restrict(user_id: user_id).
project([:user_id, :user_name, :title])
end
!
end
# get all user's tasks
rom.users_tasks(1)
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Mapping “data” to objects
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# basic attribute mapping
!
rom.mapping do
relation(:users_tasks) do
map :user_id, :user_name, :title
end
end
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# mapping embedded values
!
rom.mapping do
relation(:users_tasks) do
map :title
wrap :user do
map :id, from: :user_id
map :name, from: user_name
end
end
end
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Simplicity!
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# simple access to all relations defined in the schema
rom.users_tasks(1).to_a
# simple access to mapped objects
rom.load(rom.users_tasks(1))
# simple inserts using *just data*
rom.tasks.insert(
user_id: 1,
user_name: “Jade",
title: "Jade's First Task”
)
# simple updates using *just data*
rom.users_tasks(1).
restrict(id: 1).
update(title: "Jade's Awesome Task")
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Embrace simplicity
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Convenience can come later
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Thank You!
<3
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Resources
• Out of the tar pit paper
• Relations as the first class citizen blog post
• Ruby Relational Algebra libraries
• www.try-alf.org
• github.com/dkubb/axiom
• Ruby Object Mapper github.com/rom-rb/rom
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Photo credits
• https://www.flickr.com/photos/ntrinkhaus/12748578494
• https://www.flickr.com/photos/ntrinkhaus/12748578494
• https://www.flickr.com/photos/scottlaird/31367273
• https://www.flickr.com/photos/nanpalmero/
14373506594
• https://www.flickr.com/photos/georgiesharp/
8547779958/