# Observers or callbacks?

**URL:** <https://www.ruby-forum.com/t/observers-or-callbacks/163499>\
**Category:** Rails\
**Created:** [March 21, 2009, 12:12am UTC](https://www.ruby-forum.com/t/observers-or-callbacks/163499 "2009-03-21T00:12:49Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![tekwiz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@tekwiz](https://www.ruby-forum.com/u/tekwiz)\
**Post date:** [March 21, 2009, 12:12am UTC](https://www.ruby-forum.com/t/observers-or-callbacks/163499/1 "2009-03-21T00:12:49Z")

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Why use an Observer for a single model rather than using a callback in  
the ActiveRecord object? They seem like they work identically. Is  
there a difference I’m missing?

For example, these seem like they would do the same thing:

class User \< ActiveRecord::Base  
after\_create :send\_welcome

```
protected
  def send_welcome
    UserMailer.send_welcome(self)
  end

```

end

class UserObserver \< ActiveRecord::Observer  
def after\_create(user)  
UserMailer.send\_welcome(user)  
end  
end

– TW

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**Author:** ![tekwiz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@tekwiz](https://www.ruby-forum.com/u/tekwiz)\
**Post date:** [March 21, 2009, 2:16am UTC](https://www.ruby-forum.com/t/observers-or-callbacks/163499/2 "2009-03-21T02:16:43Z")

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Hi tekwiz,

This is excerpt is from Agile Web D. with Rails:

Callbacks are a fine technique, but they can sometimes result in a  
model class  
taking on responsibilities that aren’t really related to the nature of  
the model.  
For example, on page 385 we created a callback that generated a log  
message  
when an order was created. That functionality isn’t really part of the  
basic  
Order class—we put it there because that’s where the callback  
executed.  
Active Record observers overcome that limitation. An observer  
transparently  
links itself into a model class, registering itself for callbacks as  
if it were part  
of the model but without requiring any changes in the model itself.

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<div class="post-metadata">

**Author:** ![tekwiz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@tekwiz](https://www.ruby-forum.com/u/tekwiz)\
**Post date:** [March 21, 2009, 2:53am UTC](https://www.ruby-forum.com/t/observers-or-callbacks/163499/3 "2009-03-21T02:53:33Z")

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Thanks elioncho! I understand that it is a best practice to separate  
certain functionality out of models into observers.

I guess I should clarify my question… Is there any _technical_  
reason to use observers instead of callbacks or visa versa.

– TW

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<div class="post-metadata">

**Author:** ![tekwiz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/dfb087/32.png) [@tekwiz](https://www.ruby-forum.com/u/tekwiz)\
**Post date:** [May 8, 2009, 3:51am UTC](https://www.ruby-forum.com/t/observers-or-callbacks/163499/4 "2009-05-08T03:51:19Z")

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I’d really like to know the answer to that too!