Introduction to using MongoDB with Ruby

1. with Ruby and MongoMapper

2. What's the presentation about?
To provide a basic introduction to MongoDB
An introduction to the MongoMapper Ruby
gem and how easy, readable the code is for
persisting/querying MongoDB
Caveat - “I’ve spent a few weeks learning about
this with Ruby and MongoMapper”

3. What the heck is MongoDB?
JSON (actually BSON - binary) based
datastore with 16MB document limit
Written in C++
Distros on Linux (RPM), OSX (Brew)
Lots of different language drivers available
(Ruby, R, Erlang, Python)

4. Why would I use it?
Simplicity - Building Javascript applications
without the layers of translation between
presentation -> business logic -> data access
Scaling out - rapidly without the hassle of
sharded MySQL or Postgres with Slony.
100GB+ on a single instance.
“It's quick to develop against - this is what I
want to use it for, prototyping!”

5. What’s Similar
CouchDB - although your datastore has to be
hardcoded up front in terms of views.
● It’s hard to do query filtering etc...
● Have to query through MapReduce JS

6. Who Uses MongoDB?
● Craigslist (Everybody uses it in North
America instead of Ebay)
● SAP - SaaS based platform
● MTV
● Sourceforge - backend storage
● Firebase (Datastore as a Service)
https://www.firebase.com

7. Mental Mapping
Table = Collection
Row = JSON Document
Index = Index
Join = Embedded Document
Partition = Shard
Partition Key = Shard Key
Useful Comparison Document
http://docs.mongodb.org/manual/reference/sql-comparison/

8. There's lots of API's including a native
MongoDB REST API, but...
I'm going to use:
● Ruby 1.9
● MongoMapper Gem
● ruby-mongo-driver (well the gem is)
Simple Storage Example

9. Install the gems for MongoMapper
gem install mongo_mapper
gem install bson_ext
or put the following in your Gemfile and use
bundler (http://bundler.io/):
source "https://rubygems.org"
gem "mongo_mapper"
gem "mongomapper_search"
Pre-requisites

10. Use mongod to start the database:
mongod --rest --dbpath=/home/jholloway/mongodb
Starting MongoDB

11. Native Port
Used by the MongoDB driver - in my case the
MongoMapper gem interacts with this
http://127.0.0.1:27017
Web UI
Allows us to inspect the MongoDB
http://127.0.0.1:28017
There's also a Mongo interactive shell (mongo)
MongoDB Interfaces

12. ● I've got a number of ebay items I want to
store, specifically some retro computer
games I’m tracking prices of on Ebay
Overview

13. MongoMapper: Create a Document
Specify the ebay item definition using the
MongoMapper API
class Item
include MongoMapper::Document
key :name, String, :required => true
key :location, String
key :price, Float
end

14. MongoMapper: Save Document
Create a new item (n.b. use of Ruby symbols)
and call save on it
Item.new(:name => "Rescue from Fractalus",
:platform => "Commodore 64",
:location => "Chippenham",
:price => 2.50).save()

15. ● Let's go back to the Mongo shell
./mongo
show dbs
use myebayitems
show collections
db.items.find()
Mongo Shell: Raw Storage

16. MongoMapper: Querying Documents
Will use irb for the examples here
irb -r ebayitemsave.rb
Find all items in the collection Item:
items = Item.all()
Query all items by price > 5
items = Item.all( :price => {:$gt => 5} )

17. MongoMapper: Dynamic Finders
I can also use dynamic finders using the fields
defined on my document, awesomeness.
So in the previous example find by price...
Item.find_by_price(2.50)
puts "Item: #{item.to_mongo()}"

18. MongoMapper: Embedded Docs
Joins - deeply nested JSON documents can be
a performance issue though
Need to think about database design carefully
up-front and model it as you’d expect to query it
This is very different from a relational database
with a reporting backend
http://mongomapper.com/documentation/

19. MongoMapper: MapReduce Example
MongoDB provides an aggregation framework
for simple operations
It also provides a mapReduce() command
which you can pass Javascript (yes) to the
embedded V8 engine
n.b. Dispatches the command to each shard in
a sharded MongoDB setup

20. MongoMapper: Full Text Search
Bah !
You can do it!
MongoMapper Search Gem - didn’t work for me
https://github.com/mariopeixoto/mongomapper_search

21. MongoMapper: Plugins
Fair few of them and you can write your own
easily enough:
● Associations
● Accessible
● Callbacks
● Dirty
● Keys
● Modifiers
● Protected
● Scopes
● Serialization
● Single Collection Inheritance
● Timestamps
● Userstamps
● Validations

22. MongoMapper: In Retrospect
I’ve just broken the surface with the capabilities
of it in the past few weeks and here
Lots more investigation required into the
aggregation framework and the map reduce
functionality
But it’s much much better than CouchDB for
what I wanted to do

23. Questions
Thanks!
All the code will be up here in a Github project:
https://github.com/jph98/ebaymongo

24. By the way we’re hiring...
● Javascript/Java Developers
● Devops
● R Consultants
Email: careers@mango-solutions.com