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@@ -189,6 +189,9 @@ module ActiveRecord
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       def add_observer!(klass)
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         klass.add_observer(self)
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+        if respond_to?(:after_find) && !klass.method_defined?(:after_find)
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+          klass.class_eval 'def after_find() end'
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+        end
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       end
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   end
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 end

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@@ -143,12 +143,12 @@ class LifecycleTest < ActiveRecord::TestCase
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     assert_equal developer.name, multi_observer.record.name
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   end
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-  def test_after_find_cannot_be_observed_when_its_not_defined_on_the_model
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+  def test_after_find_can_be_observed_when_its_not_defined_on_the_model
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     observer = MinimalisticObserver.instance
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     assert_equal Minimalistic, MinimalisticObserver.observed_class
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     minimalistic = Minimalistic.find(1)
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-    assert_nil observer.minimalistic
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+    assert_equal minimalistic, observer.minimalistic
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   end
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   def test_after_find_can_be_observed_when_its_defined_on_the_model
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@@ -159,6 +159,34 @@ class LifecycleTest < ActiveRecord::TestCase
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     assert_equal topic, observer.topic
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   end
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+  def test_after_find_is_not_created_if_its_not_used
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+    # use a fresh class so an observer can't have defined an
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+    # after_find on it
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+    model_class = Class.new(ActiveRecord::Base)
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+    observer_class = Class.new(ActiveRecord::Observer)
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+    observer_class.observe(model_class)
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+
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+    observer = observer_class.instance
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+
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+    assert !model_class.method_defined?(:after_find)
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+  end
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+
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+  def test_after_find_is_not_clobbered_if_it_already_exists
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+    # use a fresh observer class so we can instantiate it (Observer is
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+    # a Singleton)
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+    model_class = Class.new(ActiveRecord::Base) do
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+      def after_find; end
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+    end
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+    original_method = model_class.instance_method(:after_find)
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+    observer_class = Class.new(ActiveRecord::Observer) do
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+      def after_find; end
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+    end
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+    observer_class.observe(model_class)
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+
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+    observer = observer_class.instance
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+    assert_equal original_method, model_class.instance_method(:after_find)
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+  end
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+
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   def test_invalid_observer
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     assert_raise(ArgumentError) { Topic.observers = Object.new; Topic.instantiate_observers }
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   end