ActiveRecord Composite Key Migrations with Rails 3.2.13

environment.rb

# add the following to the end of your environment.rb file
# monkey patching for the win!
ActiveRecord::ConnectionAdapters::ColumnDefinition.class_eval <<-'EOF'
  def to_sql
    if name.is_a? Array
      column_sql = "PRIMARY KEY (#{name.join(',')})" 
    else
      column_sql = "#{base.quote_column_name(name)} #{sql_type}"
      column_options = {}
      column_options[:null] = null unless null.nil?
      column_options[:default] = default unless default.nil?
      add_column_options!(column_sql, column_options) unless type.to_sym == :primary_key
    end
    column_sql
  end
EOF

ActiveRecord::ConnectionAdapters::ColumnDefinition.send(:alias_method, :to_s, :to_sql)

ActiveRecord::ConnectionAdapters::TableDefinition.class_eval <<-'EOF'
  def column(name, type, options = {})
    name = (name.is_a? Array) ? name : name.to_s
    type = type.to_sym

    column = self[name] || new_column_definition(@base, name, type)

    limit = options.fetch(:limit) do
      native[type][:limit] if native[type].is_a?(Hash)
    end

    column.limit     = limit
    column.precision = options[:precision]
    column.scale     = options[:scale]
    column.default   = options[:default]
    column.null      = options[:null]
    self
  end
EOF

ActiveRecord::ConnectionAdapters::SchemaStatements.class_eval <<-'EOF'
  def create_table(table_name, options = {})
    td = table_definition

    yield td if block_given?

    if(options[:id] || options[:primary_key])
      td.primary_key(options[:primary_key] || Base.get_primary_key(table_name.to_s.singularize))
    end

    if options[:force] && table_exists?(table_name)
      drop_table(table_name, options)
    end

    create_sql = "CREATE#{' TEMPORARY' if options[:temporary]} TABLE "
    create_sql << "#{quote_table_name(table_name)} ("
    create_sql << td.to_sql
    create_sql << ") #{options[:options]}"

    execute create_sql
  end
EOF

migration_example.rb

create_table "CARRIER", :primary_key => [:ID], :id => false, :force => true  do |t|
  t.string "ID",      :limit => 15,  :null => false
  t.string "NAME",    :limit => 50
end