Ruby-on-rails – the best way to override Rails ActiveRecord destroy behavior

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I have an application where I would like to override the behavior of destroy for many of my models. The use case is that users may have a legitimate need to delete a particular record, but actually deleting the row from the database would destroy referential integrity that affects other related models. For example, a user of the system may want to delete a customer with whom they no longer do business, but transactions with that customer need to be maintained.

It seems I have at least two options:

Duplicate data into the necessarily models effectively denormalizing my data model so that deleted records won't affect related data.
Override the "destroy" behavior of ActiveRecord to do something like set a flag indicating the user "deleted" the record and use this flag to hide the record.

Am I missing a better way?

Option 1 seems like a horrible idea to me, though I'd love to hear arguments to the contrary.

Option 2 seems somewhat Rails-ish but I'm wondering the best way to handle it. Should I create my own parent class that inherits from ActiveRecord::Base, override the destroy method there, then inherit from that class in the models where I want this behavior? Should I also override finder behavior so records marked as deleted aren't returned by default?

If I did this, how would I handle dynamic finders? What about named scopes?

Best Answer

If you're not actually interested in seeing those records again, but only care that the children still exist when the parent is destroyed, the job is simple: add :dependent => :nullify to the has_many call to set references to the parent to NULL automatically upon destruction, and teach the view to deal with that reference being missing. However, this only works if you're okay with not ever seeing the row again, i.e. viewing those transactions shows "[NO LONGER EXISTS]" under company name.

If you do want to see that data again, it sounds like what you want has nothing to do with actually destroying records, which means that you will never need to refer to them again. Hiding seems to be the way to go.

Instead of overriding destroy, since you're not actually destroying the record, it seems significantly simpler to put your behavior in a hide method that triggers a flag, as you suggested.

From there, whenever you want to list these records and only include visible records, one simple solution is to include a visible scope that doesn't include hidden records, and not include it when you want to find that specific, hidden record again. Another path is to use default_scope to hide hidden records and use Model.with_exclusive_scope { find(id) } to pull up a hidden record, but I'd recommend against it, since it could be a serious gotcha for an incoming developer, and fundamentally changes what Model.all returns to not at all reflect what the method call suggests.

I understand the desire to make the controllers look like they're doing things the Rails way, but when you're not really doing things the Rails way, it's best to be explicit about it, especially when it's really not that much of a pain to do so.

Related Solutions

Ruby-on-rails – the easiest way to duplicate an activerecord record

To get a copy, use the clone (or dup for rails 3.1+) method:

# rails < 3.1
new_record = old_record.clone

#rails >= 3.1
new_record = old_record.dup

Then you can change whichever fields you want.

ActiveRecord overrides the built-in Object#clone to give you a new (not saved to the DB) record with an unassigned ID.
Note that it does not copy associations, so you'll have to do this manually if you need to.

Rails 3.1 clone is a shallow copy, use dup instead...

R – What’s the cleanest way to override ActiveRecord’s find for both models and collections

You want to override find_every, which is the AR method that will ultimately run find_by_sql with the corresponding query. Overriding find won't work for customized finders, and it's just more fragile.

But to be compatible with other plugins you can't just overload this method. Instead, alias it and call the original implementation after doing what you want:

module MyPlugin
  def self.included(base)
    class << base
      alias_method :find_every_without_my_plugin, :find_every
      def find_every(*args)
        # do whatever you need ...
        find_every_without_my_plugin(*args)
      end
    end
  end
end

ActiveRecord::Base.send :include, MyPlugin

This will enable your plugin for all classes. How do you want to control which models are enabled? Maybe a standard plugin accessor?

class User < ActiveRecord::Base
  my_plugin
end

To support this you need to move the class << base to a class method (thus base should be self). Like:

module MyPlugin
  def self.included(base)
    class << base
      base.extend ClassMethods
    end
  end

  module ClassMethods
    def my_plugin
      class << self
        alias_method :find_every_without_my_plugin, :find_every
        # ...
      end
    end
  end
end

Best Answer

Related Solutions

Ruby-on-rails – the easiest way to duplicate an activerecord record

R – What’s the cleanest way to override ActiveRecord’s find for both models and collections

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