Question

I’m using a rake task to move data between databases with slightly different schemas.

This is no problem when the model names are different. For example copying information from a separate database with a “Manufacturer” model into the “Company” model of the current application:

task :copy_from_old_to_new => :environment do

  require "active_record"

  class Manufacturer < ActiveRecord::Base
  end

  Manufacturer.establish_connection(
    :adapter =>"postgresql",
    :host => "...", 
    :username => "...", 
    :database => "...")

  Manufacturer.find_each do |m|
    Company.new do |c|
      c.name = m.name
      c.location = m.geography
      c.save
    end
  end

  Manufacturer.connection.close

end

However when copying between two databases with identical model names this doesn’t work because defining the class for the external database overrides the class in the current application. Any ideas?

Answer 1

You can override the table name for any model:

class SomeModel < ActiveRecord::Base
   self.table_name = 'some_table'

If you still want you models to be named after their tables, you can scope them in some module.

Also don’t forget that multiple db-queries run faster within a transaction.

Also you can put your db-connection params in database.yml under different section and connect to it by passing its name to the establish_connection method:

class SomeModel < ActiveRecord::Base
   establish_connection :name_of_my_db_in_yml

If there are multiple models, you can make some base class and derive your models from it:

class MyBase < ActiveRecord::Base
  self.abstract_class = true # important! We don't make STI, just some abstraction.
  establish_connection :name_of_my_db_in_yml

class SomeModel < MyBase
  # connection will be established to your :name_of_my_db_in_yml db