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It’s often useful to disable ActiveRecord callbacks such as :after_save when migrating data. It’s rather easy to do:

Foo.after_create.clear
Foo.after_save.clear
... migration code ...

If you only need to disable certain actions, it’s also trivial:

Foo.after_save.reject! {|callback| callback.method.to_s == 'some_method_name' }

This sort of thing should never be used in application code, if you’re doing this then your model is broken. However, it’s great for data migrations.