Using MongoDB and a Relational Database at MongoDB Day

Building Good Relations Using MongoDB and a relational database in your apps

Hayes Davis @hayesdavis CheapTweet.com

If you’ve already got an app

You probably already have a database

It’s probably relational http://www.mbari.org/ssds/ReferenceDocuments/RDB_ER.gif

It’s probably gotten a little bit big http://www.neonlite.ca/archives/images/big%20cat.jpg

Or maybe it’s gotten huge http://www.fahad.com/pics/liger.jpg

And it’s probably pretty complicated http://www.mazes.org.uk/i/101005m.gif

Or maybe really complicated http://tommilsom.com/wp-content/ﬁles/france/maze.jpg

Which makes it harder to change http://twitter.com/dacort/status/11023722831

But, you’re not going to throw all that out http://blog.makezine.com/284163191_6f09179853_o.jpg

So let’s make NoSQL and SQL live in harmony http://curiousanimals.net/wp-content/uploads/2008/03/cat-and-dog-sleep.jpg

But ﬁrst...

Do you even need to?

We all want to play with shiny new toys http://actionfan.ﬁles.wordpress.com/2009/07/voltron_metallic-vinyl-edit.jpg

But sometimes that’s not the best plan http://www.pwn3d.us/wp-content/uploads/2006/11/voltron_1.jpg

So, give yourself a test

#1 Is my data relational?

#1 Are my data relational?

#2 Do my data access patterns lend themselves to denormaliation?

#3 Do I expect a lot of schema change?

#4 Can I drop ACID? (Atomicity, Consistency, Isolation, Durability)

#5 Do I want to support a new piece of infrastructure?

If you answered yes to any of these questions...

... at least for parts of your app...

... then MongoDB might be right for you http://www.rankopedia.com/CandidatePix/25781.gif

Where to start...

Utilities and supporting tools

Logging & analysis http://sbadrinath.ﬁles.wordpress.com/2009/03/different26rqcu3.jpg

We built Parrot http://ﬁlmfanatic.org/reviews/wp-content/uploads/2008/01/anfscd-parrot.png

Isolated subsystems http://themarkvolta.ﬁles.wordpress.com/2009/01/lost-map.jpg

Comments might be a good choice http://www.readwriteweb.com/archives/facebook_wants_to_be_your_one_true_login.php

Getting practical (in Rails, at least)

Using MongoMapper and ActiveRecord

Getting set up

conﬁg/mongodb.yml development: host: 127.0.0.1 test: host: 127.0.0.1 production: host: mongo-server.local

conﬁg/initializers/mongo.rb # Read in the config info mongo_cfg = YAML.load( IO.read("#{RAILS_ROOT}/config/mongodb.yml") )[RAILS_ENV] # Create the connection from mongodb.yml args = [mongo_cfg['host'],mongo_cfg['port']].compact MongoMapper.connection = Mongo::Connection.new(*conn_args) # Pick the Mongo database db_cfg = Rails.configuration.database_configuration[RAILS_ENV] MongoMapper.database = mongo_cfg['database'] || db_cfg['database']

Mixing your MM with your AR http://i.treehugger.com/images/2007/10/24/frankenstein-jj-001.jpg

app/models/ preferences.rb class Preferences include MongoMapper::Document key :user_id, Integer end

apps/models/user.rb class User < ActiveRecord::Base after_save :save_prefs def preferences @preferences ||= Preferences.find_or_create_by_user_id(id) end private def save_prefs @preferences.save if @preferences end end

Usage # Set any preferences you like user = User.find_by_login('thatguy') user.preferences[:foreground] = '#FF0000' user.preferences[:foo] = 'bar' user.save # Later on, you can do this user = User.find_by_login('thatguy') user.preferences[:foreground] #returns '#FF0000'

Our general solution

active-expando (very, very alpha)

Any attribute, any time # Grab a user user = User.find(1) # Now set an attribute that didn't exist before user.expandos.foreground = '#FF0000' # foreground is saved in Mongo user.save # Find any users with a red foreground color users = User.expando_all( :conditions=>{:foreground=>'#FF0000'} )

Skip expandos, use delegate class Post < ActiveRecord::Base expando_config do delegate :tags end end p = Post.find(1) p.tags = ['foo','bar'] p.save # Find any Post with the tag "foo" Post.expando_all(:conditions=>{'tags'=>'foo'})

It’s a rails plugin

It’s on GitHub (http://github.com/hayesdavis/active-expando)

Other issues

Where we’re going we don’t need migrations (or do we?) http://www.gordtep.com/ﬁles/2009/08/bttf2.jpg

Flexibility is great (until it bites you)

A general word of caution

MongoDB is a moving target

So are the tools

There will be bugs http://nitishkrishna.ﬁles.wordpress.com/2009/07/2007_there_will_be_blood_013.jpg

So, be ready to upgrade

Questions?

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Using MongoDB and a Relational Database at MongoDB Day

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