# This needs to be outside the module to work.
class JsonValidator < ActiveModel::EachValidator
  # implement the method called during validation
  def is_json?(value)
    begin
      !!JSON.parse(value)
    rescue
      false
    end
  end
  def validate_each(record, attribute, value)
    record.errors[attribute] << 'must be JSON' unless value.nil? || is_json?(value)
  end
end