Same custom validation for several fields in Rails

Question

I have four date_time fields in my model in Rails app. I want to apply the same validation method to them, so that only a valid date time could be accepted. Validation method is from earlier question on stack overflow:

  validate :datetime_field_is_valid_datetime

  def datetime_field_is_valid_datetime
    errors.add(:datetime_field, 'must be a valid datetime') if ((DateTime.parse(datetime_field) rescue ArgumentError) == ArgumentError) && !datetime_field.nil? && !datetime_field.blank?
  end

Is there more elegant way to validate these fields, other than defining four exactly same methods for every DateTime field?

Answer 1

Best solution is to create your own validator:

class MyModel < ActiveRecord::Base
  include ActiveModel::Validations

  class DateValidator < ActiveModel::EachValidator
    def validate_each(record, attribute, value)
      record.errors[attribute] << "must be a valid datetime" unless (DateTime.parse(value) rescue nil)
    end
  end
  validates :datetime_field, :presence => true, :date => true
  validates :another_datetime_field, :presence => true, :date => true
  validates :third_datetime_field, :presence => true, :date => true
end

UPD

you can share same validations this way:

  validates :datetime_field, :another_datetime_field, :third_datetime_field, :presence => true, :date => true

Answer 2

def self.validate_is_valid_datetime(field)
  validate do |model|
    if model.send("#{field}?") && ((DateTime.parse(model.send(field)) rescue ArgumentError) == ArgumentError)
      model.errors.add(field, 'must be a valid datetime')
    end
  end
end

validate_is_valid_datetime :datetime_field