Rails: Generating an Oracle DDL without Oracle installed

At my current project we are developing on Mac Minis and deploying to linux boxes. A fairly large problem with developing on Mac Minis is that there's no driver for Oracle that runs on the Intel Mac Minis.

We (painfully at times) address this problem by running Postgres locally and Oracle on our CI boxes. This works for us, but recently we ran into some pain. We needed to create SQL scripts from our schema definitions.

We store our schema definitions in the same format as a migration, but we put them all in one block, similar to the code below.

ActiveRecord::Schema.define(:version => 1) do

  create_table :accounts, :force => true do |t|
    t.column :first_name, :string
    t.column :last_name, :string
    t.column :username, :string
    t.column :password, :string
    t.column :email, :string
    t.column :company, :string
  end

  ...
end

And, we define our db:migrate to simply require this file.

task :migrate => :environment do
  ActiveRecord::Base.establish_connection(environment)
  require File.dirname(__FILE__) + '/../../db/schema/release_1.rb'
end

Since we run against Oracle on our CI boxes we could generate the DDL as a build artifact, but each time we make a change to the DDL we would need to check-in to see the changes for Oracle. This wasn't the most efficient use of our time, so we decided to get the OracleAdapter working on our MacMinis, despite not having the OCI8 drivers or oracle installed.

The code isn't the cleanest I've written, but it's also not as bad as I expected. It works for generating DDLs; however, it won't work if you have any code that requires a trip to the database to get table information (SomeActiveRecordSubClass.create is a good example of code that requires a trip).

namespace :db do
  namespace :generate do
    namespace :oracle do
      desc "generate sql ddl"
      task :ddl do
      $:.unshift File.dirname(__FILE__) + "../../../tools/fake_oci8"
      Rake::Task[:environment].execute
      file = File.open(RAILS_ROOT + "/db/oracle_ddl.sql", 'w')

      ActiveRecord::Base.instance_eval do
        def connection 
          ActiveRecord::ConnectionAdapters::OracleAdapter.new nil
        end
      end

      class ActiveRecord::Schema < ActiveRecord::Migration
        def self.define (info={}, &block)
          instance_eval(&block)
        end
      end

      ActiveRecord::Base.connection.class.class_eval do
        define_method :execute do |*args| 
          file << "#{args.first};\n"
        end
      end

      Rake::Task[:"db:migrate"].execute
      file.close
    end
  end
end

Much like a previous entry, I'm stealing the execute method to get the generated SQL. This time, I've also stolen the AR::Base.connection method and put an OracleAdapter in there. The change to AR::Schema is required because the original method updates the schema_info table at the end. Since I'm not using migrations, the update is unnecessary.

The result: An Oracle specific DDL generated without actually connecting to an Oracle database.