Dynamic dependency on mysql or postgres

Rakefile

@@ -4,6 +4,7 @@
 require 'rake'
 require 'spec/rake/spectask'
 require 'rake/rdoctask'
+require 'metric_fu'
 
 begin
   require 'jeweler'
@@ -24,9 +25,7 @@ begin
 
     # export DBMS
     gemspec.add_dependency('data_objects', '>= 0.10.2')
-    gemspec.add_dependency('mysql', '>= 2.8.1')
     gemspec.add_dependency('do_mysql', '>= 0.10.2')
-    gemspec.add_dependency('pg', '>= 0.9.0')
     gemspec.add_dependency('do_postgres', '>= 0.10.2')
 
     gemspec.add_development_dependency('rspec', '>= 1.3.0')

lib/squealer/database.rb

@@ -1,8 +1,5 @@
 require 'mongo'
 require 'data_objects'
-require 'mysql'
-require 'do_mysql'
-require 'do_postgres'
 
 require 'singleton'
 
@@ -16,6 +13,8 @@ def import_from(host, port, name)
     end
 
     def export_to(adapter, host, username, password, name)
+      require "do_#{adapter}"
+
       @@all_export_connections ||= []
       @export_do.dispose if @export_do
 
@@ -32,7 +31,7 @@ def export
     end
 
     def upsertable?
-      @export_do.is_a? DataObjects::Mysql::Connection
+      defined?(DataObjects::Mysql) && @export_do.is_a?(DataObjects::Mysql::Connection)
     end
 
     class Connection

spec/spec_helper_dbms_mysql.rb

@@ -1,4 +1,5 @@
 def create_export_db(name)
+  require 'do_mysql'
   $db_adapter = 'mysql'
   dbc = DataObjects::Connection.new("mysql://root@localhost/mysql")
   dbc.create_command("DROP DATABASE IF EXISTS #{name}").execute_non_query

spec/spec_helper_dbms_postgres.rb

@@ -1,4 +1,5 @@
 def create_export_db(name)
+  require 'do_postgres'
   $db_adapter = 'postgres'
   dbc = DataObjects::Connection.new("postgres://localhost/postgres")
   dbc.create_command("DROP DATABASE IF EXISTS #{name}").execute_non_query