Compare Validator (ActiveModel)

comparison_validator.rb

# validates :password_approval, comparison: { to: :password }
# - or -
# validates :password_approval, comparison: { to: :password, is: :equal_to }

class ComparisonValidator < ActiveModel::EachValidator
  OPERATOR_MAPPINGS = {
    equal_to: :==,
    greater_than: :>,
    greater_than_or_equal_to: :>=,
    less_than: :<,
    less_than_or_equal_to: :<=
  }
  
  def initialize(options = {})
    raise ArgumentError, ':to option must be defined' unless options[:to]
    options[:is] ||= OPERATOR_MAPPINGS.keys.first
    raise ArgumentError, "unknown comparison operator: #{options[:is]}" unless OPERATOR_MAPPINGS.key?(options[:is])
    super(options)
  end

  def validate_each(record, attribute, value)
    other_value = record.send(options[:to])
    operator = options[:is]
    unless value.send(OPERATOR_MAPPINGS[operator], other_value)
      interpolations = options.merge(value: value, other_attribute_name: record.class.human_attribute_name(options[:to]), other_value: other_value)
      record.errors.add(attribute, :"compared_#{operator}", interpolations)
    end
  end
end