How to make Guacamole - Speaker Deck

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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 / @mixxt Dirk Breuer / @railsbros_dirk

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Data Source Pattern Architectural patterns which drive the way in which the domain logic talks to the database. – Martin Fowler

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• Active Record • Data Mapper  • Table Data Gateway • Row Data Gateway • …

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NoSQL Not ACID compliant Big Data Distributed Web Scale ROFL Scale CAP Documents Flexible High Availability

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NoSQL Databases • „Not only SQL“ • Not one definition • Sometimes just a marketing buzz-fuzz

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Classifications • Document-based • Key-Value stores • Graph-based • Column stores • Time series Aggregate-based }

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Multi-Model Combine more than one approach within one database system

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Guacamole Source: https://en.wikipedia.org/wiki/File:Guacamole.jpg A dip consisting at least of ripe avocados and salt

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…and…

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gem 'guacamole' An ODM for ArangoDB to be used with Rails and other Ruby frameworks* Object Document Mapper *which is not yet finished

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• Open-Source NoSQL database • Multi-Model • Document-based • Graph-based

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Why should I use  ArangoDB in favor of  ? With ArangoDB you can perform joins  over your documents similar  to joins in relational databases.

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Before you start

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Patterns of Enterprise Application Architecture

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Ingredients

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1 Design Goal 1 Data Source Pattern 3 Supporting Libraries 1 Database driver 1 solid Test-Suite 1 Documentation

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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

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Data Source Pattern

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Data Mapper It’s a Nein! – Doch! – Ohhhh!

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+ Testability is increased + Separation of Concern + Easier to support database  features like embedded objects - The average Rails dev is  used to Active Record - Starting with Data Mapper  requires more effort

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Supporting Libraries

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spec.add_dependency 'ashikawa-core' spec.add_dependency 'virtus' spec.add_dependency 'activemodel' spec.add_dependency 'hamster' spec.add_dependency 'activesupport'

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Implementation

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Just some bits and pieces…

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The Model class Post include Guacamole::Model ! attribute :title, String attribute :body, String attribute :comments, Array[Comment] attribute :user, User end

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The Collection (a.k.a. The Mapper) class PostsCollection include Guacamole::Collection ! map do embeds :comments references :user end end

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ActiveRecord equivalent class Post < ActiveRecord belongs_to :user has_many :comments end

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Retrieving Data # Get a user by email UsersCollection.by_example(email: "[email protected]")

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Identity Map

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„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

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• Not a Cache! • Every session needs its own, fresh instance • Should be suited for concurrency (you know, just in case)

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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

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Lazy Loading

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Post#user # Proxy UsersCollection.by_key(post_document[:user_key])

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Active Model compliance

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• 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

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Caveats

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rom-rb/devtools

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Virtus and Circular Dependencies

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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

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Next Steps

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Support for Arango Query Language (AQL)

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Support for Transactions

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Support the Graph API

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https://github.com/triAGENS/guacamole Get a Nacho and dip in

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http://tfcl.de/ http://geekstammtisch.de/ https://github.com/railsbros-dirk Thanks