Should I sleep here?

rubyonrails-talk
1

Hi

I'm building an app at the moment where specific items can be added to an order and then purchased through paypal.

Becuase the items are limited, it's important to relist them quickly if the order is not completed within 5mins.

Anybody have any suggestions as to how I could go about this?

I was thinking of creating an observer for orders and including an after_create like so:

Class OrderObserver < ActiveRecord::Observer

def after_create   sleep 300 # sleep for 5 mins   if self.status > 3 # anything above 3 should be saved     return   else     self.items.each do |item|       item.update_attribute :order_id, nil     end     self.destroy   end end

Is there a better or a standard way of doing this though?

2

take a look at backgrounDRb. maybe this could be an option for you. http://backgroundrb.rubyforge.org/

in a background process you could sleep for as long as you want to, but if you try that in your main process your application might freeze for that amount of time.

3

I thought that may be the case Thanks for your help - will read up on background DRb

4

I thought that may be the case Thanks for your help - will read up on background DRb

another possibility is to have a cron job or daemon that checks for
orders that have been waiting for too long (stick a expires_at column
or something on the table). Just calling sleep is a bad idea.

Fred

5

Gavin wrote:

Anybody have any suggestions as to how I could go about this?

I was thinking of creating an observer for orders and including an after_create like so:

Class OrderObserver < ActiveRecord::Observer

def after_create   sleep 300 # sleep for 5 mins   if self.status > 3 # anything above 3 should be saved     return   else     self.items.each do |item|       item.update_attribute :order_id, nil     end     self.destroy   end end

Sorry if this response is a bit off the question's topic, but I do have an unrelated suggestion.

You have the following line in your sample code:

  if self.status > 3 # anything above 3 should be saved

I would recommend against this use of "magic numbers," such as "3" in this case. The number 3 has no meaning here. I would recommend that you use something like a "finite state machine."

There is a Ruby gem implementation of this:

Now the same line of code can be written as: if self.completed?

Now there is no ambiguity on the meaning of some "magic number." The code clearly states its intent.

6

So, would it be more appropriate to write a method like

def purchased?   if self.status > 3     return true   else     return false   end end

and then call the purchased? method to perform the check?

7

Writing more unit tests for this as we speak

Thanks for the tip Robert

PS - I presume, if I were to use constants that I would define the constants in the class itself?

8

+1 for implementing this as a cron job. Sometimes the cleanest solution is outside the framework.

9

Am I right in saying Daemons for frequent tasks (performing a specific check every minute or so) and cron jobs for less regular tasks (cleaning up sessions every week or so)?

Are Daemons resource-intensive?

10

Hi,

Check out this excelent railscast:

It is really easy & effective.

Also, Thorny Gorms has some built-in checks for form expiration:

http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/9ec5a5112548c95e

Cheers, Sazima

11

Thanks Sazima - I set up a daemon like this earlier today and it's working a treat, just wasn't sure if this was the most economic way to get the job done!

But if it's good enough for Ryan, it's good enough for me.