per_class_errors.rb

require 'pry'

module SomeRecord
  class Base
    def do_something
      raise self.class::NotFoundError.new
    end

    def self.inherited(subclass)
      subclass.const_set :NotFoundError, Class.new(SomeRecord::NotFoundError)
    end
  end

  class NotFoundError < StandardError
  end
end

class MyClass < SomeRecord::Base
  def do_something
    puts "before error"
    super
  rescue NotFoundError
    puts "in rescue"
    raise
  end
end

class User < SomeRecord::Base
end

# binding.pry

begin
  MyClass.new.do_something
  puts "did something, shouldn't see"
rescue MyClass::NotFoundError
  puts "in outer rescue"
end