Raising errors in attribute accessor overrides? - ruby-on-rails

Question

I am overriding an attribute accessor in ActiveRecord to convert a string in the format "hh:mm:ss" into seconds. Here is my code:
class Call < ActiveRecord::Base
attr_accessible :duration
def duration=(val)
begin
result = val.to_s.split(/:/)
.map { |t| Integer(t) }
.reverse
.zip([60**0, 60**1, 60**2])
.map { |i,j| i*j }
.inject(:+)
rescue ArgumentError
#TODO: How can I correctly report this error?
errors.add(:duration, "Duration #{val} is not valid.")
end
write_attribute(:duration, result)
end
validates :duration, :presence => true,
:numericality => { :greater_than_or_equal_to => 0 }
validate :duration_string_valid
def duration_string_valid
if !duration.is_valid? and duration_before_type_cast
errors.add(:duration, "Duration #{duration_before_type_cast} is not valid.")
end
end
end
I am trying to meaningfully report on this error during validation. The first two ideas that I have had are included in the code sample.
Adding to errors inside of the accessor override - works but I am not certain if it is a nice solution.
Using the validation method duration_string_valid. Check if the other validations failed and report on duration_before_type_cast. In this scenario duration.is_valid? is not a valid method and I am not certain how I can check that duration has passed the other validations.
I could set a instance variable inside of duration=(val) and report on it inside duration_string_valid.
I would love some feedback as to whether this is a good way to go about this operation, and how I could improve the error reporting.

Answer 1

First, clean up your code. Move string to duration converter to the service layer. Inside the lib/ directory create StringToDurationConverter:
# lib/string_to_duration_converter.rb
class StringToDurationConverter
class << self
def convert(value)
value.to_s.split(/:/)
.map { |t| Integer(t) }
.reverse
.zip([60**0, 60**1, 60**2])
.map { |i,j| i*j }
.inject(:+)
end
end
end
Second, add custom DurationValidator validator
# lib/duration_validator.rb
class DurationValidator < ActiveModel::EachValidator
# implement the method called during validation
def validate_each(record, attribute, value)
begin
StringToDurationConverter.convert(value)
resque ArgumentError
record.errors[attribute] << 'is not valid.'
end
end
end
And your model will be looking something like this:
class Call < ActiveRecord::Base
attr_accessible :duration
validates :duration, :presence => true,
:numericality => { :greater_than_or_equal_to => 0 },
:duration => true
def duration=(value)
result = StringToDurationConverter.convert(value)
write_attribute(:duration, result)
end
end