Robby on Rails

This is great to know. I’ve used observers before, mostly in the context of caching views, but not for observing events in models. It seems to me that if you have more than one before_[whatever] or after_[whatever] in your model it’s probably best to move them into an observer. I have a few models that have a ton of these callbacks that will be nice to move out into another location. Thanks!

Why not just use ActiveRecord callback hooks instead of Observers? Are Observers more powerful or is it just a matter of preference?

Yeah, I’d like to know the benefits too. Can you shed some light on this Robby?

(I’d also like the ability to use the logger from within an observer, but that’s another issue)

Eric A

> Why not just use ActiveRecord callback hooks instead of Observers?

• if a model could become invalid should the triggered action not take place, use AR hooks.
• if the triggered action modifies the model (ex: pre-render and cache textile text in the model), use AR hooks.

Otherwise use/consider observers.

Creating a new record may be cause for some action to be triggered. If that action is tangential to the model which triggers it then it makes sense to keep that action separate. The AR docs have some logical examples that should help you see the point of using observers.

Observers use the same AR callbacks. You don’t use observers as a replacement for AR callbacks; observers augment the usefulness of the AR callbacks.

Do observers “block” the rendering?

If you have a timely job to be done upon a model.save, would it pause the rendering until it is done?

I am implementing a module that will email a comment, but this will go to a few 100 people. I don’t want the submitter to wait for minutes while this is happening.

Thank you, Michael

hi, there :) and http://api.rubyonrails.org//

Good post :)
I refered to http://guides.rubyonrails.org/action_mailer_basics.html

I am a bit unclear about observers.

Consider the set up below:

model/part_mailer.rb —-—-—-—-—-- class PartMailer < ActionMailer::Base @admin_email = ‘admin@sample.com’ @from_email = ‘admin-sales@sample.com’

def created_succesfully(part)
  recipients user.email, @admin_email
  from @from_email
  subject "MyApp - New part created." 
  body :user => user
end

model/part_observer.rb —-—-—-—-—-——

class PartObserver < ActiveRecord::Observer def after_create(part) PartMailer.deliver_created_succesfully(part) end end

It looks as if I can only pass in the object of the given class into the observer. In the case above, ‘part’ is the only one that is being passed by to deliver_created_successfully in model/part_observer.rb. part_mailer.rb)? I tried looking at the api docs and http://guides.rubyonrails.org/action_mailer_basics.html to no success. Can someone please shed some light into this?

Can I pass more objects to the method, created_successfully (model/

Thanks! :)

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It appears that the Agile Web Development with Rails book is still encouraging people to do the following in order to load an Observer.

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