Define a convention for descendants and subclasses.

The former should be symmetric with ancestors and include all children. However, it should not include self since ancestors + descendants should not have duplicated. The latter is symmetric to superclass in the sense it only includes direct children.

By adopting a convention, we expect to have less conflict with other frameworks, as Datamapper. For this moment, to ensure ActiveModel::Validations can be used with Datamapper, we should always call ActiveSupport::DescendantsTracker.descendants(self) internally instead of self.descendants avoiding conflicts.

1 files changed, 3 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/observer.rb b/activerecord/lib/active_record/observer.rb
index 5f80bd86df..d2ed643f35 100644
--- a/activerecord/lib/active_record/observer.rb
+++ b/activerecord/lib/active_record/observer.rb
@@ -94,7 +94,7 @@ module ActiveRecord
 
     def initialize
       super
-      observed_subclasses.each { |klass| add_observer!(klass) }
+      observed_descendants.each { |klass| add_observer!(klass) }
     end
 
     def self.method_added(method)
@@ -108,8 +108,8 @@ module ActiveRecord
 
     protected
 
-      def observed_subclasses
-        observed_classes.sum([]) { |klass| klass.send(:descendants) }
+      def observed_descendants
+        observed_classes.sum([]) { |klass| klass.descendants }
       end
 
       def observe_callbacks?