Dentaku expression validator

expression_validator.rb

class ExpressionValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    begin
      Dentaku(value)
    rescue Exception => e
      record.errors[attribute] << (options[:message] || e.message)
    end
  end
end

For use with Dentaku.

Save to app/validators/expression_validator.rb and include in your model like so:

class Product < ActiveRecord::Base
  validates :expression, expression: true
end