Re: Validation method vs. After Save & Rollback

> 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.

> On Jul 23, 2:03 pm, Philip Hallstrom <phi...@...> wrote:
>> On Jul 22, 2008, at 7:53 PM,validkeyswrote:
>>
>>
>>
>>
>>
>>> 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)
>>
>> 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
> >

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group.
To post to this group, send email to rubyonrails-talk@...
To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe@...
For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---