MongoDB and Ruby on Rails

Using MongoDB with Ruby on Rails
presented by Ryan Fischer, Founder of 20spokes

What is covered

• Why we use MongoDB and Ruby on Rails

• Choices made for Object Mapper

• Simple to get started!

Using MongoDB with Ruby on Rails

• Fast in-place updates with atomic modiﬁers

• Ruby on Rails is productive!

• Object Mappers available for MongoDB

• Mongo Ruby Driver

Mobile / Web

• Ruby on Rails makes REST easy, making APIs easier.

• Render responses as text, JSON, or XML

• Geospatial indexing for location based queries.

• Location-centric websites and mobile applications.

Why we chose MongoDB

• Cowrite - collaborative writing web application

• Versioning needed

• Originally using GridFS

• Travel720 - Gift registry web site

• Self contained relations can take advantage of embedding documents

Mongo Object Mappers for Ruby

• MongoMapper

• Mongoid

• Mongo ODM

• MongoModel

Why we chose Mongoid

• Excellent documentation

• Active community

• Compatibility with other projects/gems

• Similar API to ActiveRecord

• Uses ActiveValidation

• Mongoid Extras: Caching, Paranoid Documents, Versioning, Timestamping,
Composite Keys

Compatible Gems with Mongoid

• Devise - Authentication solution for Rails based on Warden. Supports
Mongoid out of box.

• Carrierwave - simple and ﬂexible way to upload ﬁles from Ruby Applications.
Supports grid_fs.

• Geocoder - complete geocoding solution for Rails. Adds geocoding by street
or IP address, reverse geocoding, and distance queries.

• Mongoid-rspec - RSpec matchers and macros for Mongoid.

Getting Started

Include in Gem ﬁle
gem "mongoid", "~> 2.3"
gem "bson_ext", "~> 1.4"

Run the install for Mongoid

rails generate mongoid:config

That’s it!

mongoid.yml
development:
host: localhost
database: geekbusters_development

test:
host: localhost
database: geekbusters_test

production:
host: <%= ENV['MONGOID_HOST'] %>
port: <%= ENV['MONGOID_PORT'] %>
username: <%= ENV['MONGOID_USERNAME'] %>
password: <%= ENV['MONGOID_PASSWORD'] %>
database: <%= ENV['MONGOID_DATABASE'] %>
# slaves:
# - host: slave1.local
# port: 27018
# - host: slave2.local
# port: 27019

Developing with MongoDB/Mongoid

• Generating models is the same using the console as with ActiveRecord.

• rails generate model Team name:string city:string
location:array

• No migrations needed!

• Take advantage of embedded documents in models where applicable for
increased performance.

• Store large ﬁles using GridFS

Fields available for Mongoid

• Array • Range

• BigDecimal (Stored as a String) • String

• Boolean • Symbol

• Date • Time

• DateTime

• Float

• Hash

• Integer

Mongoid Document

class Team
include Mongoid::Document
include Mongoid::Timestamps

field :name, type: String
field :city, type: String
field :location, :type => Array

validates :name, :city, :presence => true

end

Persisting in the Controller

def create
Team.create(:city => "New York", :name => "Giants")
end

def update
@team = Team.find(params[:id])
@team = Team.update_attributes(params[:team])
end

Indexing
class Team

field :name, type: String
index :name, unique: true
end

Indexing on multiple ﬁelds -

index(
[
[ :name, MONGO::ASCENDING ]
[ :city, MONGO::ASCENDING ]
]
)

Indexing

To create indexes in the database use the rake task

rake db:mongoid:create_indexes

Or conﬁgure to autocreate in mongoid.yml (not recommended)

defaults: &defaults
autocreate_indexes: true

Relations in Models

• Associations between models can be embedded or referenced

• NO JOINS!

• Objects that are referenced involve a separate query

• Embedded documents can be very efﬁcient with reducing queries to one
while managing the size of the document

• One to One, One to Many, and Many to Many relations available

Relations in Mongoid - Embedded

• Embedded Relations - stored inside other documents in the database.
class Blog
embeds_many :posts
end

class Post
embedded_in :blog
end

Embedded Posts

{ "_id" : ObjectId("4e9ba47fcdffba523f000004"),
"name" : "Geekbusters Blog",
"posts" :
[
{"content" : "Slimer is right behind you.",
_id" : ObjectId("4e9ba47fcdffba523f000005")}
]
}

Polymorphic Behavior
class Image
embeds_many :comments, as: :commentable
end

class Document
embeds_many :comments, as: :commentable
end

class Comment
embedded_in :commentable, polymorphic: true
end

Relations in Mongoid - Referenced

Referenced Relations - stores reference to a document in another collection,
typically an id

class Blog
has_many :posts, dependent: :delete
end

class Post
belongs_to :blog
end

Many to Many Relationship

class Tag
has_and_belongs_to_many :posts
end

class Post
has_and_belongs_to_many :tags
end

Querying

• Queries are of type Criteria, which is a chainable and lazily evaluated wrapper
to a MongoDB dynamic query.

• Chainable queries include:
all_in includes
all_of limit
also_in near
and not_in
any_of only
asc order_by
desc skip
distinct where
excludes without

Query Examples

Team.near(location: [20.70, 38.15]).limit(20)

Team.any_in(names: ["Giants", "Bears", "Lions"])

Team.find_or_create_by(name: "Giants")

Team.where(name: "Cowboys").destroy_all

Versioning with Mongoid

• Embeds a version of the object on each save.

• Can skip versioning and also set the max versions.

• Add to model -

include Mongoid::Versioning

Versioning Example
{"_id" : ObjectId("4e9ba7fdcdffba52d6000004"),
"content" : "Impossible. I am too loud to fall asleep to.",
"created_at" : ISODate("2011-10-17T03:58:53Z"),
"title" : "Impossible to sleep to - this guy.",
"updated_at" : ISODate("2011-10-17T03:58:53Z"),
"version" : 3,
"versions" : [
{"title" : "Who is asleep?",
"content" : "Wake up the guy next to you if they are asleep.
Thanks.",
"version" : 1,
"created_at" : ISODate("2011-10-17T03:58:53Z")},
{"title" : "Who is asleep?",
"content" : "Impossible. I am too loud to fall asleep to.",
"created_at" : ISODate("2011-10-17T03:58:53Z"),
"version" : 2 } ]
}

And More

• Identity Map

• Callbacks

• Scopes

• Dirty Tracking

Testing Rails with MongoDB

• RSpec-Mongoid provides test matchers

• RSpec does not refresh the database with each test run.

• Database Cleaner to the rescue. It be setup to truncate a database before
running tests. Add below after installing the DatabaseCleaner Gem.

config.before(:suite) do
DatabaseCleaner.strategy = :truncation
DatabaseCleaner.orm = "mongoid"
end

Hosting Options

• Heroku is a widely used cloud hosting for Ruby on Rails

• MongoHQ and MongoLab both have add on options

• Options and pricing are similar

Thanks!!

Email: ryan.ﬁscher@20spokes.com

Twitter: @ryanﬁscher20

Check out Geekbusters on Github

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