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Implement a Data Source Pattern for a Multi-Model NoSQL database
or
How to make Guacamole
16.4.2014 / cologne.rb / @mixxtDirk Breuer / @railsbros_dirk
Data Source Pattern
Architectural patterns which drive the way in which the domain logic
talks to the database.
– Martin Fowler
• Active Record
• Data Mapper
• Table Data Gateway
• Row Data Gateway
• …
NoSQL
Not ACID compliant
Big DataDistributed
Web Scale
ROFL Scale
CAP
Documents
Flexible
High Availability
NoSQL Databases
• „Not only SQL“
• Not one definition
• Sometimes just a marketing buzz-fuzz
Classifications
• Document-based
• Key-Value stores
• Graph-based
• Column stores
• Time series
Aggregate-based}
Multi-Model
Combine more than one approach within one database system
Guacamole
Source: https://en.wikipedia.org/wiki/File:Guacamole.jpg
A dip consisting at least of ripe avocados and salt
…and…
gem 'guacamole'An ODM for ArangoDB to be used with Rails and other Ruby frameworks*
Object Document Mapper
*which is not yet finished 😜
• Open-Source NoSQL database
• Multi-Model
• Document-based
• Graph-based
Why should I useArangoDB in favor of
<any other document store>?
With ArangoDB you can perform joinsover your documents similar
to joins in relational databases.
Before you start
Patterns of Enterprise Application Architecture
Ingredients
1 Design Goal
1 Data Source Pattern
3 📦 Supporting Libraries
1 Database driver
1 solid Test-Suite
1 📦 Documentation
Design Goal
• Support building web applications with Ruby on Rails or other Rack-based frameworks
• Focus on easy integration in Views and the general workflow
• Reflect the nature of NoSQL in general and ArangoDB in particular
Data Source Pattern
Data MapperIt’s a
Nein! – Doch! – Ohhh
h!
+ Testability is increased
+ Separation of Concern
+ Easier to support databasefeatures like embedded objects
- The average Rails dev isused to Active Record
- Starting with Data Mapper requires more effort
Supporting Libraries
spec.add_dependency 'ashikawa-core' spec.add_dependency 'virtus' spec.add_dependency 'activemodel' spec.add_dependency 'hamster' spec.add_dependency 'activesupport'
Implementation
Just some bits and pieces…
The Model
class Post include Guacamole::Model !
attribute :title, String attribute :body, String attribute :comments, Array[Comment] attribute :user, User end
The Collection (a.k.a. The Mapper)
class PostsCollection include Guacamole::Collection !
map do embeds :comments references :user end end
ActiveRecord equivalent
class Post < ActiveRecord belongs_to :user has_many :comments end
Retrieving Data
# Get a user by email UsersCollection.by_example(email: "p.pie@cupcakes.com")
Identity Map
„Ensures that each object gets loaded only once by keeping every loaded object in a map. Looks up objects
using the map when referring to them.“
– Martin Fowler
• Not a Cache!
• Every session needs its own, fresh instance
• Should be suited for concurrency (you know, just in case)
module Guacamole class IdentityMap class << self def store(object) @_map = _map.put(key_for(object), object) object end !
def retrieve(klass, key) _map.get key_for(klass, key) end !
def _map @_map ||= Hamster.hash end end end end
Lazy Loading
Post#user
#<User>
Proxy
UsersCollection.by_key(post_document[:user_key])
Active Model compliance
• Really useful, not only for Rails
• A lot of Gems build on top of Active Model
• A lot of useful features (i.e. Validations)
• Not related to the Active Record pattern
Caveats
rom-rb/devtools
Virtus and Circular Dependencies
class Author extend ActiveSupport::Autoload include Guacamole::Model !
autoload :Book, 'models/book' !
attribute :name, String attribute :books, Array[Book] end
class Book extend ActiveSupport::Autoload include Guacamole::Model !
autoload :Author, 'models/author' !
attribute :title, String attribute :author, Author end
This is not very Ruby
Next Steps
Support for Arango Query Language (AQL)
Support for Transactions
Support the Graph API
http://tfcl.de/
http://geekstammtisch.de/
https://github.com/railsbros-dirk
Thanks
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