Validates DateTime values in a Rails app

date_time_validator.rb

# this sucker takes care of validating datetime fields before rails gets there and
# messes everything up. it should preserve the local time zone from the user input, 
# and check for nil. takes date strings of the format m/d/yyyy m:h (am/pm)

# this goes in the model
validates_with DateTimeValidator, :fields => [:add_date]

# this goes in some place like lib/date_time_validator.rb
class DateTimeValidator < ActiveModel::Validator
  DATETIME_FORMAT = "%m/%d/%Y %I:%M %P"
  def validate(record)
    options[:fields].each do |field|
      begin
        # gotta use the actual string and not the rails fucked time that it 'conveniently' converts to UTC
        record[field] = Time.strptime(record.send("#{field}_before_type_cast"), DATETIME_FORMAT)                                                  
      rescue ArgumentError
        record.errors.add(field, "is either invalid or blank")
      end 
    end 
  end 
end

#TIL You can avoid the .send with:

record.attributes_before_type_cast[field.to_s]