Introduction to MongoDB Persisting dynamic data

1. SOMETHING SOMETHING
MONGO
Introduction to MongoDB
Persisting dynamic data with MongoDB, MongoMapper &
metaprogramming
Saturday 1 May 2010

2. 1
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• Bernard Grymonpon
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• Openminds BVBA
• Rails Hosting & Rails-shop ribbit
• @wonko_be - @openminds_be
Top sites deserve
maximum uptime
openminds.be
tailored hosting solutions
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4. WHAT IS IT?
• Document-based data store
• JSON-style data (BSON)
• Built for speed (searching)
• Massive amounts of data (humongous)
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5. SCALING
• Has built in High Availability (Replication and Failover)
• Has built in Auto-sharding
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6. SPEED
• GridFS as document store
• In-place updates
• Indexes
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7. QUERYING
• rich syntax
• sorting (order by), skipping (limit)
• field selection
• mapreduce (group by)
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8. SCHEMALESS
• No fixed set of fields when storing an document
• title: “foo”, author: “bar”
• title: “arrrr”, author: “captain”, when: “today”
• We get empty fields when selecting non-existing data
• find will return “when” as empty when selecting all data
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9. USE...
YES NO
• (most) Websites • Transactions
• Caching • Lots of joins
• Scalabilty • Fixed datasets (science,...)
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10. START USING IT
• MongoDB in google: www.mongodb.org - Quickstart
• make a directory
• download mongodb
• unpack
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11. START USING IT
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12. START USING IT
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13. QUERYING
> db.arrrrcamp.save({talk: "MongoDB", who: "Bernard"})
> db.arrrrcamp.find()
{
"_id" : ObjectId("4b681a1ecf1bcfea49f4b2ae"),
"talk" : "MongoDB",
"who" : "Bernard"
}
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14. MORE QUERYING
> db.arrrrcamp.find({who: "Bernard")
{
"_id" : ObjectId("4b681a1ecf1bcfea49f4b2ae"),
"talk" : "MongoDB",
"who" : "Bernard"
}
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15. MORE QUERYING
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18. gem install mongo_mapper
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19. gem install mongo_mapper
gem install mongo_ext
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20. require 'mongo_mapper'
MongoMapper.database = ‘arrrrcamp’
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21. class Presenter
include MongoMapper::Document
end
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22. class Presenter
include MongoMapper::Document
key :name, String
key :confirmed, Boolean
key :keywords, Array
key :presentation, Presentation
end
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23. presenter = Presenter.new({
:name => “Bernard”,
:confirmed => true,
:keywords => [“Openminds”, “geek”]
})
presenter.save
presenter.destroy
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24. EMBEDDED DOCUMENT
include MongoMapper::EmbeddedDocument
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25. ACTIVERECORD, ANYONE?
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26. MONGOMAPPER HAS
• validates_*
• before_save / after_update / ...
• has_many / belongs_to
• timestamps!
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27. STORING CUSTOM
DATATYPES
• to_mongo - serialize your own data to a known mongo-
storable data structure (string, array,...)
• from_mongo - unserialize your data and return an object (of
“self ”)
• both are class methods (!)
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28. class Keywords
def initialize(array)
@words = array
end
def to_a
@words
end
class << self
def to_mongo(value)
value.is_a?(Keywords) ? value.to_a : value
end
def from_mongo(value)
value ? self.new(value) : nil
end
end
end
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29. class Presenter
include MongoMapper::Document
key :keywords, Keywords
end
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30. DYNAMIC DATA
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31. INHERITANCE
class Page class BlogPost < Page
key :permalink, String key :content, String
key :title, String has_many :comments
end end
class Redirect < Page
key :destination, String
end
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32. MODULAR
module Authentication
def self.included(base)
base.key :password, String
base.key :salt, String
base.key :login, String
end
end
class Person
include MongoMapper::Document
include Authentication
end
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33. MULTISITE WEBSHOP
EXAMPLE
per instance data gathering
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34. WHAT TO BUILD
• Ordering system - multiple stores: shoes, tv’s, mobile phones
• One system
• Each shop has its own fields to require for an order
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35. SOLUTION
• metaprogramming: dynamically generate a class for each site
• dynamically add the fields to the mongomapper
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36. SITE-CLASS
• Can be a Mongo-document
• Can be an ActiveRecord object
• Can be a (Rails 3) ActiveModel object (REST?)
• Has to “respond_to? :id” and “respond_to? :order_fields”
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37. ORDER CLASS: MM
class Order
include MongoMapper::Document
key :order_id, String
end
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38. FACTORY-PATTERN
class Order
class << self
def for_site(site)
klass = Class.new(self)
klass.order_fields = site.order_fields
Object.const_set("OrderForSite#{site.id}", klass)
klass
end
end
end
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39. DYNAMIC DOCUMENT
BUILDING
class Order
def order_fields=(fields)
fields.each do |field|
key field, String
end
end
end
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40. class Order
include MongoMapper::Document
key :order_id, String
class << self
def for_site(site)
klass = Class.new(self)
klass.order_fields = site.order_fields
Object.const_set("OrderForSite#{site.id}", klass)
klass
end
def order_fields=(fields)
fields.each do |field|
key field, String
end
end
end
end
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41. TRY IT OUT
current_site.order_fields
#=> [“field1”, “field2”]
@order = Order.for_site(current_site).new
#=> #<OrderForSite2172858380 field1: nil, field2: nil,
order_id: nil>
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45. Q&A
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