Application migration from Java EE/PHP to Rails 3 - Models

Well, ok, then I'll just let everybody know what I did in the hopes that someone else will find it useful.

I decided to go with regular rails models with the external database configured in database.yml:

# MySQL.  Versions 4.1 and 5.0 are recommended.
#
# Install the MySQL driver:
#   gem install mysql
# On Mac OS X:
#   sudo gem install mysql -- --with-mysql-dir=/usr/local/mysql
# On Mac OS X Leopard:
#   sudo env ARCHFLAGS="-arch i386" gem install mysql -- --with-mysql-            config=/usr/local/mysql/bin/mysql_config
#       This sets the ARCHFLAGS environment variable to your native architecture
# On Windows:
#   gem install mysql
#       Choose the win32 build.
#       Install MySQL and put its /bin directory on your path.
#
# And be sure to use new-style password hashing:
#   http://dev.mysql.com/doc/refman/5.0/en/old-client.html
development:
  adapter: mysql
  encoding: utf8
  reconnect: false
  database: myapp_development
  pool: 5
  username: db_user
  password: db_pass  
  socket: /private/tmp/mysql.sock 

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  adapter: mysql
  encoding: utf8
  reconnect: false
  database: myapp_test
  pool: 5
  username: db_user
  password: db_pass  
  socket: /private/tmp/mysql.sock

production:
  adapter: mysql
  encoding: utf8
  reconnect: false
  database: my_app_production
  pool: 5
  username: db_user
  password: db_pass   
  socket: /private/tmp/mysql.sock 

## This is the external DB ##
external_app:
  adapter: mysql
  encoding: utf8
  reconnect: false
  database: external_db
  pool: 5
  username: db_user
  password: db_pass
  socket: /private/tmp/mysql.sock

Then create the models with the standard rails generator:

rails g model external_app_name/model_name --no-migrations

As the models are in an existing, non-rails db I don't want migrations, do what you want here.

This creates a basic empty model in app/models/external_app_name/model_name.rb which I then modify thusly:

class ExernalApp::ModelName < ActiveRecord::Base

  establish_connection :external_app # from database.yml
  set_table_name :external_app_table_name
  set_primary_key :id

end

From there you can continue development as though it was a normal rails model (which, of course, it is ; ).

This method will also create whatever tests and other junk that your normal generator creates so you can just move forward. Presumably you could also do this with a scaffold, etc if there was some good reason (wasn't for me, just need models).

NOTE:

This also creates a module in app/models/external_app.rb that looks like:

    module ExternalApp
      def self.table_name_prefix
        'external_app_'
      end
    end

Initially I set prefix to '' but doesn't seem to have any impact as created.

I know none of this is rocket science or even very far up the ladder of computer science, but it's an organizational/process thing that I think will keep life as easy and 'rails way' as possible during this part of the project.

Hope this helps!