← models | persistence →
current status
- install Ruby
- install Rails
- install MySQL
- install The Ruby Racer
- (probably don’t need to)
install Vim
current status
$ rails new the-truth
$ cd the-truth
$ vim config/database.yml
$ vim Gemfile
$ rails generate model journalist name
$ rails generate model article title body:text journalist:references
$ rake db:migrate
$ vim test/unit/{journalist,article}_test.rb
- If the first thing you type, when writing a Ruby app,
is: ‘rails’, you’ve already lost the architecture game.
— Uncle Bob Martin
why persist?
- what do we want?
- TIME TRAVEL!
- when do we want it?
- THAT’S IRRELEVANT!
\o/ yay, databases! \o/
- A database is a black hole into which you put your data.
If you’re lucky, you’ll get it back again.
If you’re very lucky, you’ll get it back in a form you can use.
— Charlie Gibbs - ‘It looks like you’re creating a database. Most likely
you’d like it in Latin1 encoding with Swedish collation.’
No, MySQL, no, I wouldn’t.
— James Higgs
\o/ yay, databases! \o/
- relational? MySQL, PostgreSQL, SQLite
- document? CouchDB, MongoDB
- in memory? Redis
- graph databases? Neo4j
- directory services? LDAP
- file-based? YAML Record, PStore (!)
polyglot persistence
Martin Fowler: The Future is not just NoSQL, it’s Polyglot Persistence
← models | persistence →
- When I open up a Rails project and the models dir is full of 100% ActiveRecord classes I shudder. Model ≠ Persistence.
— Ben Mabey - We need something better. Persistance and logic are two separate responsibilities that every Rails app combines.
— Steve Klabnik
← models ! persistence →
- backend independence!
- no shortcuts! explicit shortcuts!
- easier modelling!
- future-proof(er) design!
← models ! persistence →
- cleaner, simpler tests!
- faster tests!
- separate persistence driver testing!
- Rails is not your app – don’t unit-test it!
← models ? persistence →
- performance?
- (perceived?) compexity?
- YAGNI?
- Just Use NullDB™?
it’s object-oriented
- The biggest reason—scratch that, the only reason—is to make our apps easier to change. The only constant in life is change, and that goes double for software projects. […] Rails is reaching a point at the time of writing where a lot of projects are starting to mature, and a lot of developers are realizing their projects aren’t nearly as easy to modify as they used to be. — Avdi Grimm, Objects on Rails
it’s object-oriented
- Attempts to predict which parts of a codebase will need to change, and to structure it accordingly, have ended badly more often than not. Part of the nature of change is that you often don’t know beforehand what is going to need change. […] Much like premature optimization, premature change management usually misses the mark.
— Avdi Grimm, Objects on Rails
please mister how do I do it
- move logic out of data objects
- decorators
- composition
- AOP: aspect-oriented programming
- DCI: data + context + interaction
decorators
- e.g., objects for views
- better than per-class helpers
- Draper
- SimpleDelegator
class Address
# extend with your favourite persistence solution
end
class Address
# extend with your favourite persistence solution or:
attr_accessor :street, :postcode, :city, :country
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end
class Address
# extend with your favourite persistence solution or:
attr_accessor :street, :postcode, :city, :country
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end
# 9 Queen Street
# Edinburgh EH2 1JQ
# Scotland
class Address
# extend with your favourite persistence solution or:
attr_accessor :street, :postcode, :city, :country
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end
class ScottishAddress
def formatted
[street, "#{city} #{postcode}", country].join "\n"
end
endrequire 'delegate'
class Address
# extend with your favourite persistence solution or:
attr_accessor :street, :postcode, :city, :country
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end
class ScottishAddress < SimpleDelegator
def formatted
[street, "#{city} #{postcode}", country].join "\n"
end
endaddress = Address.new street: '9 Queen Street',
postcode: 'EH2 1JQ', city: 'Edinburgh', country: 'Scotland'
address = Address.new street: '9 Queen Street',
postcode: 'EH2 1JQ', city: 'Edinburgh', country: 'Scotland'
scottish_address = ScottishAddress.new address
address = Address.new street: '9 Queen Street',
postcode: 'EH2 1JQ', city: 'Edinburgh', country: 'Scotland'
scottish_address = ScottishAddress.new address
scottish_address.country # => Scotland
address = Address.new street: '9 Queen Street',
postcode: 'EH2 1JQ', city: 'Edinburgh', country: 'Scotland'
scottish_address = ScottishAddress.new address
scottish_address.country # => Scotland
puts scottish_address.formatted
# 9 Queen Street
# Edinburgh EH2 1JQ
# Scotlanddecorators
- let your data objects be data objects
- logic in bussiness? behaviour? objects
- bonus: ease of testing + reuse
composition over inheritance
- Inheritance is a code smell. There, I said it. — Chris Strom
- compose domain objects from data objects
- Forwardable
class Address
# extend with your favourite persistence solution or:
attr_accessor :street, :postcode, :city, :country
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end
class Address
# extend with your favourite persistence solution or:
attr_accessor :street, :postcode, :city, :country
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end
class Person
# extend with your favourite persistence solution or:
attr_accessor :given_names, :surname, :title
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end
class Address
# extend with your favourite persistence solution or:
attr_accessor :street, :postcode, :city, :country
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end
class Person
# extend with your favourite persistence solution or:
attr_accessor :given_names, :surname, :title # *
def initialize args = {}
args.each { |key, value| send "#{key}=", value }
end
end* please read Personal names around the world
class ScottishEnvelopeAddress
def initialize args
@person = args.fetch :person, Person.new
@address = args.fetch :address, Address.new
end
# Dr P. Rate
# 9 Queen Street
# Edinburgh EH2 1JQ
# Scotland
end
class ScottishEnvelopeAddress
def initialize args
@person = args.fetch :person, Person.new
@address = args.fetch :address, Address.new
end
def formatted
["#{title} #{given_names} #{surname}",
street, "#{city} #{postcode}", country].join "\n"
end
endrequire 'forwardable'
class ScottishEnvelopeAddress
extend Forwardable
def initialize args
@person = args.fetch :person, Person.new
@address = args.fetch :address, Address.new
end
def_delegators :@person, :given_names, :surname, :title
def_delegators :@address, :street, :postcode, :city, :country
def formatted
["#{title} #{given_names} #{surname}",
street, "#{city} #{postcode}", country].join "\n"
end
endperson = Person.new given_names: 'P.', surname: 'Rate', title: 'Dr'
person = Person.new given_names: 'P.', surname: 'Rate', title: 'Dr'
address = Address.new street: '9 Queen Street',
postcode: 'EH2 1JQ', city: 'Edinburgh', country: 'Scotland'
person = Person.new given_names: 'P.', surname: 'Rate', title: 'Dr'
address = Address.new street: '9 Queen Street',
postcode: 'EH2 1JQ', city: 'Edinburgh', country: 'Scotland'
sea = ScottishEnvelopeAddress.new person: person, address: address
person = Person.new given_names: 'P.', surname: 'Rate', title: 'Dr'
address = Address.new street: '9 Queen Street',
postcode: 'EH2 1JQ', city: 'Edinburgh', country: 'Scotland'
sea = ScottishEnvelopeAddress.new person: person, address: address
sea.surname # => 'Rate'
sea.city # => 'Edinburgh'
person = Person.new given_names: 'P.', surname: 'Rate', title: 'Dr'
address = Address.new street: '9 Queen Street',
postcode: 'EH2 1JQ', city: 'Edinburgh', country: 'Scotland'
sea = ScottishEnvelopeAddress.new person: person, address: address
sea.surname # => 'Rate'
sea.city # => 'Edinburgh'
puts sea.formatted
# Dr P. Rate
# 9 Queen Street
# Edinburgh EH2 1JQ
# Scotlandcomposition over inheritance
- domain models composed from data models
- persistence as a component?
- …so you can dependency-inject it
- Making Little Classes out of Big Ones
- Composing Ruby
AOP
- In Smalltalk, everything happens somewhere else.
— Adele Goldberg - making things happen elsewhere
- persisting objects
when things happen to them - logging with RCapture
class PrimeSelector
endclass PrimeSelector
def initialize numbers
@numbers = numbers
end
endclass PrimeSelector
def initialize numbers
@numbers = numbers
end
def primes
@numbers.select { |number| prime? number }
end
endclass PrimeSelector
def initialize numbers
@numbers = numbers
end
def primes
@numbers.select { |number| prime? number }
end
private
def prime? number
(2..Math.sqrt(number).floor).all? { |i| (number % i).nonzero? }
end
endrequire 'logger'
require 'rcapture'
class Logging
endrequire 'logger'
require 'rcapture'
class Logging
def initialize log
@log = Logger.new log
add_logging
end
endrequire 'logger'
require 'rcapture'
class Logging
def initialize log
@log = Logger.new log
add_logging
end
private
def add_logging
PrimeSelector.class_eval { include RCapture::Interceptable }
end
endrequire 'logger'
require 'rcapture'
class Logging
def initialize log
@log = Logger.new log
add_logging
end
private
def add_logging
PrimeSelector.class_eval { include RCapture::Interceptable }
PrimeSelector.capture_pre methods: :prime? do |point|
@log.debug "prime? #{point.args.first}"
end
end
endrequire 'logger'
require 'rcapture'
class Logging
def initialize log
@log = Logger.new log
add_logging
end
private
def add_logging
PrimeSelector.class_eval { include RCapture::Interceptable }
PrimeSelector.capture_pre methods: :prime? do |point|
@log.debug "prime? #{point.args.first}"
end
PrimeSelector.capture_post methods: :prime? do |point|
@log.debug "prime? → #{point.return}"
end
end
endLogging.new $stdout
PrimeSelector.new(2..10).primes
Logging.new $stdout
PrimeSelector.new(2..10).primes
# D, [2012-06-29T00:25:21.746960 #31892] DEBUG -- : prime? 2
# D, [2012-06-29T00:25:21.747180 #31892] DEBUG -- : prime? → true
# D, [2012-06-29T00:25:21.747265 #31892] DEBUG -- : prime? 3
# D, [2012-06-29T00:25:21.747347 #31892] DEBUG -- : prime? → true
# D, [2012-06-29T00:25:21.747460 #31892] DEBUG -- : prime? 4
# D, [2012-06-29T00:25:21.747550 #31892] DEBUG -- : prime? → false
# D, [2012-06-29T00:25:21.747629 #31892] DEBUG -- : prime? 5
# D, [2012-06-29T00:25:21.747740 #31892] DEBUG -- : prime? → true
# D, [2012-06-29T00:25:21.747818 #31892] DEBUG -- : prime? 6
# D, [2012-06-29T00:25:21.747900 #31892] DEBUG -- : prime? → false
# D, [2012-06-29T00:25:21.747977 #31892] DEBUG -- : prime? 7
# D, [2012-06-29T00:25:21.748072 #31892] DEBUG -- : prime? → true
# D, [2012-06-29T00:25:21.748149 #31892] DEBUG -- : prime? 8
# D, [2012-06-29T00:25:21.748232 #31892] DEBUG -- : prime? → false
# D, [2012-06-29T00:25:21.748309 #31892] DEBUG -- : prime? 9
# D, [2012-06-29T00:25:21.748406 #31892] DEBUG -- : prime? → false
# D, [2012-06-29T00:25:21.748482 #31892] DEBUG -- : prime? 10
# D, [2012-06-29T00:25:21.748563 #31892] DEBUG -- : prime? → falseAOP
- work with you objects
as if the memory was forever - make a separate presistence layer
that hooks into state-changing methods - …or explicitly route through that layer
and make it persist the changes afterwards
DCI
- data + context + interaction
- data objects (1:1 persistence?)
- per-role behaviour: mixins extending data
module Data
class Person
# …
end
class Address
# …
end
endmodule Roles
module Landlord
def rent_a_place address, person
# rent only if the person is credible (as a tenant)
end
end
module Tenant
def credible?
# …
end
end
endmodule Contexts
class RentingAPlace
def initialize address, person_a, person_b
@address = address
@landlord = person_a.extend Roles::Landlord
@tenant = person_b.extend Roles::Tenant
end
end
def call
# …
@landlord.rent_a_place @address, @tenant
# …
end
endaddress = … # probably fetch from persistence store
person_a = … # probably fetch from persistence store
person_b = … # probably fetch from persistence store
renting = Contexts::RentingAPlace.new address, person_a, person_b
renting.callDCI
- it’s not about persistence
- it’s a fundamental architectural change
- data | behaviour separation
- read The Right Way to Code DCI in Ruby
going way overboard (?)
- it’s all about objects
- why not hide persistance altogether?
- Candy
Candy: transparent persistence in MongoDB
require 'candy'
Candy: transparent persistence in MongoDB
require 'candy'
class Conference
include Candy::Piece
end
Candy: transparent persistence in MongoDB
require 'candy'
class Conference
include Candy::Piece
end
src = Conference.new
# connects to localhost:27017 and ‘chastell’ db if needed
# and saves a new document to the ‘Conference’ collection
Candy: transparent persistence in MongoDB
require 'candy'
class Conference
include Candy::Piece
end
src = Conference.new
# connects to localhost:27017 and ‘chastell’ db if needed
# and saves a new document to the ‘Conference’ collection
src.location = 'Edinburgh' # method_missing resaves
Candy: transparent persistence in MongoDB
require 'candy'
class Conference
include Candy::Piece
end
src = Conference.new
# connects to localhost:27017 and ‘chastell’ db if needed
# and saves a new document to the ‘Conference’ collection
src.location = 'Edinburgh' # method_missing resaves
src.events = { parties: { saturday: 'Zoë Keating concert' } }
src.events.parties.saturday #=> 'Zoë Keating concert'
world domination plans
- don’t
rails g model-drive you design - various ways to persist objects (PStore!)
- learn about your persistence layer’s features
- disassociate models from persistence
- play with decorators, composition, AOP, DCI
- read Personal names around the world
class Integer
def simple_prime?
(2..Math.sqrt(self).floor).all? { |i| (self % i).nonzero? }
end
end
class Integer
def simple_prime?
(2..Math.sqrt(self).floor).all? { |i| (self % i).nonzero? }
end
def clever_prime?
return true if self == 2
return false if self.even?
3.step(Math.sqrt(self).floor, 2).all? { |i| (self % i).nonzero? }
end
end
require 'prime'
class Integer
def simple_prime?
(2..Math.sqrt(self).floor).all? { |i| (self % i).nonzero? }
end
def clever_prime?
return true if self == 2
return false if self.even?
3.step(Math.sqrt(self).floor, 2).all? { |i| (self % i).nonzero? }
end
end
require 'benchmark'
require 'prime'
class Integer
def simple_prime?
(2..Math.sqrt(self).floor).all? { |i| (self % i).nonzero? }
end
def clever_prime?
return true if self == 2
return false if self.even?
3.step(Math.sqrt(self).floor, 2).all? { |i| (self % i).nonzero? }
end
end
range = 2..1_000_000
Benchmark.bmbm do |bench|
bench.report('simple:') { range.each &:simple_prime? }
bench.report('clever:') { range.each &:clever_prime? }
bench.report('stdlib:') { range.each &:prime? }
end$ ruby prime_bench.rb
Rehearsal -------------------------------------------
simple: 24.690000 0.000000 24.690000 ( 24.709989)
clever: 13.120000 0.000000 13.120000 ( 13.130319)
stdlib: 33.480000 0.000000 33.480000 ( 33.500611)
--------------------------------- total: 71.290000sec
user system total real
simple: 24.780000 0.000000 24.780000 ( 24.804631)
clever: 13.180000 0.000000 13.180000 ( 13.194177)
stdlib: 33.120000 0.000000 33.120000 ( 33.158172)
