AJAYA

Recently I had to look at various options to do proper validation before destroying a model. Rails doesn't have a validate_before_destroy callback but it does have before_destroy.

We could implement a simple validation before destroy two ways:

Option 1: Implement the callback before_destroy in the model class itself.

Implement the method before_destroy in the model code itself.

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class Organization < ActiveRecord::Base
  def before_destroy
     # Do your thing
     # Return true or false
     self.expired?
  end
end

From the rails documentation

Callbacks are generally run in the order they are defined, with the exception of callbacks defined as methods on the model, which are called last.

So with that said, any associations that are defined in the model would be destroyed before model.destroy call is aborted and there no way of going back.

Option 2: Register the callback before_destroy at the top of the method

In your model code declare at the top

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class Organization < ActiveRecord::Base
  before_destroy :okToDelete
  protected
  def okToDelete
     # Do your thing
     # Return true or false
     self.expired?
  end
end

In this case, if you define the callback at the very top of the model class (before any other association declaration), then rails makes sure to call this callback first and aborts the destroy call.

You can also pass a block to the callback to keep it simple.

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class Organization < ActiveRecord::Base
  before_destroy do |r|
     # Do your thing
     # Return true or false
     r.expired?
  end
end

or even less

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class Organization < ActiveRecord::Base
  before_destroy {|r| r.expired?}
end