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Beyond the ORM
an introduction to DataMapper 2
RuLu 2012
Sunday, June 24, 12
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Piotr Solnica
• codebenders.com
• solnic.eu
• github.com/solnic
• @_solnic_
Sunday, June 24, 12
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4 Facts about This Talk
• It has 2 sections: “ActiveRecord
Retrospective” and “DataMapper 2”
• It has 2 obligatory pictures of a cat
• It has only 1 quote from Martin
Fowler’s PoEAA book
• It has only 16 code examples
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ActiveRecord
Retrospective
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ActiveRecord
Pattern Facts
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Active Record Pattern Facts
• Simple ORM Pattern
• Designed for simple usecases where the
business domain is simple. ie. basic
CRUD
• Mixes together data & behavior
• 1:1 mapping between database schema &
objects (means tight coupling with the
db)
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ActiveRecord
in Rails
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class User < ActiveRecord::Base
end
Active Record in Rails
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Active Record in Rails
(User.methods.sort - Object.methods.sort).count
# => 391
391
new public class methods...
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WHAT??!! I’m perfectly fine!!!
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• Persistence
• Validations
• Associations
• Life cycle hooks
• Typecasting
• Mass-assignment security
• ...and much much more!
Active Record
retrospective
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Active Record
retrospective
• Slow test suites
• Lack of real unit tests
• God objects
• Code hard to reuse and extend
• Code hard to refactor
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I don’t think I can take it Anymore!
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I don’t care if
we can create a
blog in 15
minutes
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but I do care if
we can work on a
project for 15
months and keep
it in a good
shape
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DataMapper 2
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DataMapper 2
“A layer of Mappers that moves data between
objects and a database while keeping them
independent of each other and the mapper itself.”
Martin Fowler
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DataMapper 2
Repository
Mapper & Session
Domain Model
Validation Serialization Extensions
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Domain Model
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Domain Model
class City
attr_reader :name, :lat, :lng
def initialize(attributes)
@name, @lat, @lng = attributes.values_at(
:name, :lat, :lng
)
end
end
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Domain Model
class CityMapper < DataMapper::Mapper
map :name, :lat, :lng
end
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Domain Model
city = City.new(
name: 'Kraków',
lat: 123456.789,
lng: 987654.321
)
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Domain Model
class GeoLocation
include Virtus::ValueObject
attribute :lat, Float
attribute :lng, Float
end
class City
include Virtus
attribute :name, String
attribute :location, GeoLocation
end
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Domain Model
class CityMapper < DataMapper::Mapper
map :name
map :location, to: [ :lat, :lng ]
end
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Session
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Session
class Person
include Virtus
attribute :name, String
attribute :city, City
end
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Session
class PersonMapper < DataMapper::Mapper
map :name
has 1, :city
end
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Session
city = City.new(
name: 'Kraków',
location: {
lat: 123456789.123,
lng: 987654321.987
}
)
person = Person.new(name: 'Piotr')
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Session
DataMapper.session do |session|
session.track(city)
session.track(person)
person.city = city
session.insert(person)
session.commit
end
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Repository
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Repository
Repository
Relation
Optimizer
Datastore Adapter
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Repository
• Complete support for all relational algebra
operations
• All operations can be run in-memory
• Can be extended to support any kind of a
datastore
• Can be used with multiple different
databases
• Designed to support per database
optimizations
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Repository
relation = Veritas::Relation.new([
[ :id, Integer ], [ :name, String ], [ :color, String ] ],
[
[ 1, 'Nut', 'Red' ],
[ 2, 'Bolt', 'Green' ],
[ 3, 'Screw', 'Blue' ],
[ 4, 'Screw', 'Red' ],
[ 5, 'Cam', 'Blue' ],
[ 6, 'Cog', 'Red' ],
]
)
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Repository
# projection
new_relation = relation.project([ :id ])
# removal
new_relation = relation.remove([ :name ])
# rename
new_relation = relation.rename(id: :other_id,
name: :other_name)
# restriction
new_relation = relation.restrict { |r|
r.color.eq('Red').or(r.color.eq('Blue'))
}
# natural join
new_relation = relation.join(other)
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Repository
include Veritas
adapter = Adapter::DataObjects.new(
"postgres://localhost/test")
header = [ [ :id, Integer ], [ :name,
String ], [ :color, String ] ]
relation = Relation::Base.new(
'items', header)
gateway = Relation::Gateway.new(
adapter, relation)
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Repository
new_relation = gateway.restrict { |r|
r.color.eq('Red').or(r.color.eq('Blue'))
}
new_relation.to_a
# SELECT "id", "name", "color"
# FROM items
# WHERE (
# "color" = 'Red' OR "color" = 'Blue'
# )
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What’s Done
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What’s Done
• Veritas
• Veritas DataObject Adapter for PostgreSQL
• Veritas Optimizer
• Virtus (Domain Model features)
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Work in Progress
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Work in Progress
• “write” support for Veritas
• Mapper
• Session/Unit of Work
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Work in Progress
• Validations
• Migrations
• Constraints
• Extension Interfaces
• More Veritas adapters (sqlite, MySQL,
MongoDB, Riak etc.)
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Development
Process
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Development Process
• All “levels” of API are treated with the
same amount of care & love
• Using metric tools to verify code quality
• Mutation testing with Heckle
• 100% YARD documentation coverage
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Virtus Project
on CodeClimate
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Resources
• https://github.com/datamapper/dm-
core/wiki/Roadmap
• https://github.com/dkubb/veritas
• https://github.com/dkubb/veritas-do-
adapter
• https://github.com/solnic/virtus
• https://github.com/solnic/dm-mapper
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THANKS!
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