how to subclass active record to call a method on all save and destroy actions

rubyonrails-talk
1

I'm looking for a way to subclass active record (I'll refer to the subclass I want to create as NewActiveRecord) so that I can call different methods on a save or destroy action on all models which sub class NewActiveRecord

I dont want to use before_save or any of the other regular call back methods as I want to be able to use these call backs in the models which subclass NewActiveRecord without having to call super everytime I use them.

Anyone have any ideas about how I can do this?

Cheers

Tony

2

Use ActiveRecord::Observer instead of ActiveRecord::Callbacks?

http://www.robbyonrails.com/articles/2007/04/28/q-a-activerecord-observers-and-you http://api.rubyonrails.org/classes/ActiveRecord/Observer.html

3

You probably want to set self.abstract_class = true.

Fred

4

Thanks for the observer link, they would work nicely but I need to be able to stop a model from saving or destroying, if the additional method i call returns false.

Basically what I'm trying to do is add some authentication methods into all my active record models so that whenever a save or destroy, and also a association is added the authentication method checks that the user has privileges to do this.

@Frederick

Thanks, I've heard that using self.abstract_class = true will allow me to sub class ActiveRecord, I need to know which single method in ActiveRecord is best to override to add the authentication methods. Do you know which would be best?, or could you point me in the direction of some good resources on ActiveRecord

Cheers

Tony

5

For extending ActiveRecord the fairly new "Pro ActiveRecord" book from APress is pretty good.

I'm not sure I'd recommend it for an introduction/only reference to AR (AWDR 2ed does a better job IMHO) but for advanced things like extending AR, it's the best resource I've found as yet.

6

We don’t do that kinda stuff in the Ruby world.

We use modules instead, so we can “mix in” that behavior.

In lib/ar_extentions.rb

module MyActiveRecordExtentions

def save(*args)

if some_condition

super(*args) # do the original

else

return false # or do your own stuff

end

end

def destroy

return false

end

end

Then all I need to do is

class User < ActiveRecord::Base

include MyActiveRecordExtensions

end

If you really want to see how this works in action, take a look at the acts_as_paranoid plugin. It uses this technique to mark records as deleted instead of actually deleting them, by overriding the destroy method. It’s a good place to start learning about this kinda stuff.

7

Thanks to all those who responded

I'll have a look at acts_as_paranoid and see what the best way forward is