Make ActiveRecord 4.1 aware of native postgresql enums

patch.rb

# PostgreSQL enums support (adapted from https://coderwall.com/p/azi3ka)
# Should be fixed in Rails >= 4.2 (https://github.com/rails/rails/pull/13244)
# put this code in an initializer file
raise "Remove this patch!" if Rails.version >= "4.2.0"
module ActiveRecord
  module ConnectionAdapters
    class PostgreSQLAdapter
      module OID
        class Enum < Type
          def type_cast(value)
            value.to_s
          end
        end
      end

      def enum_types
        @enum_types ||= begin
          result = execute 'SELECT DISTINCT t.oid, t.typname FROM pg_type t JOIN pg_enum e ON t.oid = e.enumtypid', 'SCHEMA'
          Hash[ result.map { |v| [ v['oid'], v['typname'] ] } ]
        end
      end

      private

      def initialize_type_map_with_enum_types_support(type_map)
        initialize_type_map_without_enum_types_support(type_map)

        # populate enum types
        enum_types.reject { |_, name| OID.registered_type? name }.each do |oid, name|
          type_map[oid.to_i] = OID::Enum.new
        end
      end
      alias_method_chain :initialize_type_map, :enum_types_support
    end

    class PostgreSQLColumn
      private

      def simplified_type_with_enum_types(field_type)
        case field_type
        when *Base.connection.enum_types.values
          field_type.to_sym
        else
          simplified_type_without_enum_types(field_type)
        end
      end
      alias_method_chain :simplified_type, :enum_types
    end
  end
end

Updated version that works with rails 4.1