PullMonkey Blog

Modularized Models and Associations in ActiveRecord

Have you ever encountered this error?

wrong constant name X::YAssociationExtension

I found this error when dealing with acts_as_versioned for one my models. I would have found it eventually with any association I would have setup in this case, so it is not acts_as_versioned's fault.
I have an application with various parts so I create some of my models like this:

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./script/generate model module_name::model_name

So the fix is pretty simple, instead of winding up with ModuleName::ModelAssociationExtension or whatever, you want your extention module name to be ModelAssociationExtension.
Here is the method where the code breaks for me:

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def create_extension_modules(association_id, block_extension, extensions)
  if block_extension
    extension_module_name = "#{self.to_s}#{association_id.to_s.camelize}AssociationExtension"

    silence_warnings do
      Object.const_set(extension_module_name, Module.new(&block_extension))
    end
    Array(extensions).push(extension_module_name.constantize)
  else
    Array(extensions)
  end
end

Here is the fix, on line 3, you will note the demodulize addition:

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def create_extension_modules(association_id, block_extension, extensions)
  if block_extension
    extension_module_name = "#{self.to_s.demodulize}#{association_id.to_s.camelize}AssociationExtension"

    silence_warnings do
      Object.const_set(extension_module_name, Module.new(&block_extension))
    end
    Array(extensions).push(extension_module_name.constantize)
  else
    Array(extensions)
  end
end

I threw the corrected code into a library - RAILS_ROOT/lib/fix_active_record_create_extension_for_modules.rb. Make sure to open up the necessary modules to overwrite the method itself, I.e., like this:

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module ActiveRecord
  module Associations
    module ClassMethods
      # the code above fits right here
    end
  end
end

Short and sweet, let me know if you have a better method for handling this.

Ruby on Rails – Multiple database connections

Found a need for this information while answering questions on railsforum.
So, let's say that we want to use two databases and let's even say that we want to use an Oracle database and a MySQL database. How can this be done? To start, we must decide which database will be our default database. In this scenario, I chose MySQL. Let's see what that looks like:

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# in your database.yml file
development:
  adapter: mysql
  username: root
  password: 
  database: example_development

So we have all seen that before. Now all of our active record models will use this mysql connection.
But, I need to use data from an oracle database, so let's setup that connection:

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# in your database.yml file
development:
  adapter: mysql
  username: root
  password: 
  database: example_development

oracle_development:
  adapter: oracle
  username: root
  password: 
  database: example_oracle_development

Neat, we have two development connections. Now we have to tell which models to use which connection. Well, actually, we just need to tell the oracle models to connect to oracle_development, all the other models will default to development. I have a model named user, and it's records are kept in an oracle database. Our user model looks like this initially:

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#RAILSROOT/app/models/user.rb
class User < ActiveRecord::Base 
end

The line we need to add is this:

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establish_connection :oracle_development

Even better, we can make this dynamic, so when we are in the test or production environment, we don't need to change the establish_connection line.

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# use RAILS_ENV where RAILS_ENV is generally development, test or production
establish_connection "oracle_#{RAILS_ENV}"

So the final product could look something like this:

database.yml

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dev_basics: &dev_basics
  username: root
  password: 

<% %w(development test production).each do |env| %>
<%= env %>:
  <<: *dev_basics
  adapter: mysql
  database: example_<%= env %>

oracle_<%= env %>:
  <<: *dev_basics
  adapter: oracle
  database: example_oracle_<%= env %>
<% end %>

Oracle model example

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class User < ActiveRecord::Base 
  establish_connection "oracle_#{RAILS_ENV}"
end

That should be it.