Are you getting the error message, “NameError: uninitialized constant” from Rails? I was too, and the solution was a simple change to my models. I have two models with “has_many :through”, for my “events” and “people” tables:

class Event < ActiveRecord::Base
  has_many :memberships
  has_many :people, :through => :memberships
end

And:

class Person < ActiveRecord::Base
  has_many :memberships
  has_many :events, :through => :memberships
end

The join table is “memberships”, and the problem was in its model:

class Membership < ActiveRecord::Base
  validates_presence_of :event_id, :person_id
  belongs_to :people
  belongs_to :events
end

It is a subtle problem; the model looks OK. However, the “belongs_to” statements should point to the models of the other two tables, not the names of the tables themselves. The models are Event and Person, so the join model should be:

class Membership < ActiveRecord::Base
  validates_presence_of :event_id, :person_id
  belongs_to :person
  belongs_to :event
end

It took me a while to see the problem because it is so subtle, even though the answer is everywhere. Hopefully spelling it out here will help someone.

I just started getting back into Ruby on Rails, after a hiatus while I battled with Leopard server. I discovered that setting up my Rails development environment in Leopard wasn’t as perfectly straightforward as it was in Tiger.

I installed the binary distribution of MySQL, and proceeded to install the mysql ruby gem to connect to it. First, the build failed because it didn’t know where to look for the mysql client libraries, then it failed again because by default the Makefile tries building for both PPC and Intel architectures.

To make a long story short, the solution is to add an ARCHFLAGS environment variable specifiying your architecture, and to provide the path to mysql_config on the command line. For the former, add:

ARCHFLAGS="-arch i386"

To your /etc/bashrc (assuming you use the default shell, bash), and open a new terminal or run ‘bash’. If you’re on PPC architecture, change “i386″ to “ppc”. Then try the gem again with the path to mysql_config appended, like so:

sudo gem install mysql -- --with-mysql-config=/usr/local/mysql/bin/mysql_config

That is all on one line.

Ruby on Rails developer and teacher Peter Marklund, of Stockholm, has published slides from his five day introductory course on Ruby on Rails. It provides a great summary of many of Rails’ features and benefits, including a summary of Ruby syntax for common tasks.