I had several requests in UserVoice to provide a Many to Many tutorial in Rails. This is a demonstration of how to put together a "has and belongs to many" association and a "has many through" association.

This is somewhat basic to Ruby on Rails, but important if you need to associate different models.

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Many to Many Associations in Ruby on Rails – A Teach Me To Code Tutorial

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My Equipment:

	Mackie PROFX12 12-Channel Compact Effects Mixer with USB
	Sony MDR7506 Professional Large Diaphragm Headphone
	Roland R-05 Studio WAVE/MP3 Recorder
	Transcend 32 GB Class 10 SDHC Flash Memory Card (TS32GSDHC10E) (for the Roland R-05)
	Griffin Technology iMic USB Audio Device
	Doctor Who TARDIS USB Hub Doctor Who TARDIS USB Hub Model #DR115
	QuickVoice Recorder
	Rolls MM11 Microphone Muting Switch Designed to Temporarily Mute a Balanced XLR Signal
	Heil PR-40 Dynamic Studio Recording Microphone
	Heil Sound SM-2 Shockmount for PR-30 and PR-40 Champagne
	Heil Sound PL-2T Overhead Broadcast Boom (Standard)

Podcasting Club Setup:

	Behringer Xenyx 802 Premium 8-Input 2-Bus Mixer with Xenyx Mic Preamps and British EQs
	Shure SM58-CN Cardioid Dynamic Vocal Microphone with Cable
	On Stage Foam Ball-Type Mic Windscreen, Black
	Hamilton Nu-Era Tabletop Mic Stand
	JVC HA-V570 Supra-Aural Headphones

My Podcasting Setup

When preparing to add some layout features to JotRod, I realized it was a Rails 3.0.9 application. Here's a quick rundown on upgrading to Rails 3.1.3.

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Upgrading JotRod to Rails 3.1.3

In order to get someone a timeline in JotRod, we need followers and following lists to compile the Jots from. This means that we need to add a new ColumnFamily called Followers and another one called Following. We don't have the joins capability from relational databases to do this for us.

I'm going to hijack the User model's database connection to create the ColumnFamilies. (We don't have migrations, yet.) Here's what I ran in the rails console:
cf_def = CassandraThrift::CfDef.new(:keyspace => "JotRod", :name => "Followers")
User.connection.add_column_family(cf_def)
cf_def = CassandraThrift::CfDef.new(:keyspace => "JotRod", :name => "Following")
User.connection.add_column_family(cf_def)
Now that we have the ColumnFamilies, I want to have syntax like this to define the relationships on the User model:
list :followers, :User
list :following, :User
This should provide the following API:

#followers - returns an array of users as specified from the Followers ColumnFamily
#followers<<(user)  - adds the user to the User object's followers list if it's not already there

and a similar API for following.

Sandra's repository

JotRod's repository

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Followers and Following

In the Jots (like tweets) in JotRod, I needed to generate a hash on creation as the key for the Jots. So, I determined that the easiest way to do that was to include ActiveModel Callbacks.

The module is pretty simple to add to your classes. Here's a demo of how to add it to Sandra.

Sandra's repository

JotRod's repository

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ActiveModel Callbacks

Here's an introduction to creating a Rails connector gem for an ORM with a model generator.

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Many to Many Associations in Ruby on Rails – A Teach Me To Code Tutorial

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