rails4.2 Postgresqlの配列リテラルを配列に変換

varying_array_parsable.rb

# app/models/concerns/varying_array_parsable.rb
module VaryingArrayParsable
  extend ActiveSupport::Concern

  class VaryingArrayParser
    # @see {https://github.com/rails/rails/blob/4-2-stable/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb}
    # Loads pg_array_parser if available. String parsing can be
    # performed quicker by a native extension, which will not create
    # a large amount of Ruby objects that will need to be garbage
    # collected. pg_array_parser has a C and Java extension
    begin
      require 'pg_array_parser'
      include PgArrayParser
    rescue LoadError
      require 'active_record/connection_adapters/postgresql/array_parser'
      include ActiveRecord::ConnectionAdapters::PostgreSQL::ArrayParser
    end
  end

  module ClassMethods
    private

    # @param value [String] varying arrayカラムの値
    # @return [Array] 型キャスト後の配列
    def cast_to_array(value)
      @pg_parser ||= VaryingArrayParser.new
      @pg_parser.parse_pg_array(value)
    end
  end
end