# Validation method vs. After Save & Rollback **URL:** \ **Category:** Rails\ **Created:** [July 23, 2008, 4:53am UTC](https://www.ruby-forum.com/t/validation-method-vs-after-save-rollback/143832 "2008-07-23T04:53:56Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![validkeys](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/da6949/32.png) [@validkeys](https://www.ruby-forum.com/u/validkeys)\ **Post date:** [July 23, 2008, 4:53am UTC](https://www.ruby-forum.com/t/validation-method-vs-after-save-rollback/143832/1 "2008-07-23T04:53:56Z")
Hey Guys, Again, I am just learning Rails, so I am asking advice here. I have a model called Company which has many Owners. The Owners model indicates the name of the owner and their share (as a percentage) of the company. The total shares for any one company can not be more than 100%. So if I have 10 owners each with 10% of the company and I update one of the owners and set their share to 11%, I should be given a warning message. This is what I have done in my Owner model: def more\_than\_100\_given\_away? # =\> find the total share company = Company.find(company\_id) company\_total\_share = company.total\_share # =\> This is summing the old value if changed? if changes[“share”] # =\> Changes to a model are stored in the changes array on the instance, the array has 2 value [“from\_value”, “to\_value”] old\_value = changes[“share”][0].to\_f # =\> Convert To Float new\_value = changes[“share”][1].to\_f new\_total\_share = company\_total\_share - old\_value + new\_value new\_total\_share \> 100.01 else false # validation succeeds end else false # validation succeeds end end It is working for me just fine, but I wanted to know if there was a better (less NOOB looking way to do this) Thanks! ---
**Author:** ![validkeys](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/da6949/32.png) [@validkeys](https://www.ruby-forum.com/u/validkeys)\ **Post date:** [July 23, 2008, 8:04pm UTC](https://www.ruby-forum.com/t/validation-method-vs-after-save-rollback/143832/2 "2008-07-23T20:04:12Z")
On Jul 22, 2008, at 7:53 PM, validkeys wrote: > So if I have 10 owners each with 10% of the company and I update one > if changed? > else > false # validation succeeds > end > end > > It is working for me just fine, but I wanted to know if there was a > better (less NOOB looking way to do this) For the most the above seems reasonable. There are a couple of things I’d watch out for though. - Near as i can tell a company could give away 100.009 shares. Sure, . 009 isn’t that much, but it could be. And it’s more than 100. Of course dealing with float rounding sucks. Don’t know if it’s an option, but you may want to consider storing the total number of shares for a company and track the number of shares per owner. That keeps everything in integer values. If you want to get an owner’s percentage of ownership do the calculation then, but only for display purposes. - The other problem is concurrency. What if I update two records at the same time and set them both to own 60% (assume individually they would succeed). They’ll both succeeed if I time it right. So you should wrap this in a transaction so that can’t happen. -philip ---
**Author:** ![validkeys](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/da6949/32.png) [@validkeys](https://www.ruby-forum.com/u/validkeys)\ **Post date:** [July 23, 2008, 10:57pm UTC](https://www.ruby-forum.com/t/validation-method-vs-after-save-rollback/143832/3 "2008-07-23T22:57:18Z")
Thanks Philip, would you mind clarifying the wrapping in a transaction? Im just not quite sure what the means/entails ---
**Author:** ![validkeys](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/da6949/32.png) [@validkeys](https://www.ruby-forum.com/u/validkeys)\ **Post date:** [July 24, 2008, 7:04pm UTC](https://www.ruby-forum.com/t/validation-method-vs-after-save-rollback/143832/4 "2008-07-24T19:04:59Z")
> Thanks Philip, would you mind clarifying the wrapping in a > transaction? Im just not quite sure what the means/entails You want to ensure that that piece of code can only run at once at a time. Transaction isn’t probably the best word for it. Synchronized lock, mutex, etc. Google around for those terms.