ActiveRecord.Base attribute accessor recommendation

The documentation for ActiveRecord::Base suggest overloading attribute accessors like this:

def length=(minutes)
  write_attribute(:length, minutes.to_i * 60)
end

Using this with update_attributes with { :length=>"6d" } will result in a silent conversion to 6, ignoring any validation. I haven't figured out the way to do this for integers (probably match against a regex) but for floats I'd use

def length=(minutes)

write_attributes(:length, Kernel.Float(minutes)*60.0)

recue ArgumentError

write_attributes(:length, minutes)

end

so that validation will still do their thing, etc.