Avoid checking dependent scopes unless necessary.

lib/friendly_id/active_record_adapter/slugged_model.rb

@@ -84,6 +84,7 @@ def update_scope
       # Update the slugs for any model that is using this model as its
       # FriendlyId scope.
       def update_dependent_scopes
+        return unless friendly_id_config.class.scopes_used?
         if slugs(true).size > 1 && @new_friendly_id
           friendly_id_config.child_scopes.each do |klass|
             Slug.update_all "scope = '#{@new_friendly_id}'", ["sluggable_type = ? AND scope = ?",

lib/friendly_id/configuration.rb

@@ -64,7 +64,7 @@ class Configuration
     attr_accessor :reserved_words
 
     # The method or relation to use as the friendly_id's scope.
-    attr_accessor :scope
+    attr_reader :scope
 
     # The string that separates slug names from slug sequences. Defaults to "--".
     attr_accessor :sequence_separator
@@ -102,6 +102,24 @@ def reserved_error_message(word)
       [method, reserved_message % word] if reserved? word
     end
 
+    def scope=(scope)
+      self.class.scopes_used = true
+      @scope = scope
+    end
+
+    # This will be set if FriendlyId's scope feature is used in any model. It is here
+    # to provide a way to avoid invoking costly scope lookup methods when the scoped
+    # slug feature is not being used by any models.
+    def self.scopes_used=(val)
+      @scopes_used = !!val
+    end
+
+    # Are scoped slugs being used by any model?
+    # @see Configuration.scoped_used=
+    def self.scopes_used?
+      @scopes_used
+    end
+
     %w[approximate_ascii scope strip_non_ascii use_slug].each do |method|
       class_eval(<<-EOM)
         def #{method}?

test/active_record_adapter/scoped_model_test.rb

@@ -121,7 +121,6 @@ def teardown
           Resident.friendly_id_config.send(:associated_friendly_classes)
         end
       end
-
     end
   end
-end
+end