1 files changed, 28 insertions, 25 deletions

diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index a549b28f16..cbb5b99a05 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -7,8 +7,8 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :_reflections
-      class_attribute :aggregate_reflections
+      class_attribute :_reflections, instance_writer: false
+      class_attribute :aggregate_reflections, instance_writer: false
       self._reflections = {}
       self.aggregate_reflections = {}
     end
@@ -483,28 +483,7 @@ module ActiveRecord
       # Returns +true+ if +self+ is a +has_one+ reflection.
       def has_one?; false; end
 
-      def association_class
-        case macro
-        when :belongs_to
-          if polymorphic?
-            Associations::BelongsToPolymorphicAssociation
-          else
-            Associations::BelongsToAssociation
-          end
-        when :has_many
-          if options[:through]
-            Associations::HasManyThroughAssociation
-          else
-            Associations::HasManyAssociation
-          end
-        when :has_one
-          if options[:through]
-            Associations::HasOneThroughAssociation
-          else
-            Associations::HasOneAssociation
-          end
-        end
-      end
+      def association_class; raise NotImplementedError; end
 
       def polymorphic?
         options[:polymorphic]
@@ -545,7 +524,7 @@ module ActiveRecord
           end
         end
 
-        # returns either nil or the inverse association name that it finds.
+        # returns either false or the inverse association name that it finds.
         def automatic_inverse_of
           if can_find_inverse_of_automatically?(self)
             inverse_name = ActiveSupport::Inflector.underscore(options[:as] || active_record.name.demodulize).to_sym
@@ -629,6 +608,14 @@ module ActiveRecord
       def macro; :has_many; end
 
       def collection?; true; end
+
+      def association_class
+        if options[:through]
+          Associations::HasManyThroughAssociation
+        else
+          Associations::HasManyAssociation
+        end
+      end
     end
 
     class HasOneReflection < AssociationReflection # :nodoc:
@@ -639,6 +626,14 @@ module ActiveRecord
       def macro; :has_one; end
 
       def has_one?; true; end
+
+      def association_class
+        if options[:through]
+          Associations::HasOneThroughAssociation
+        else
+          Associations::HasOneAssociation
+        end
+      end
     end
 
     class BelongsToReflection < AssociationReflection # :nodoc:
@@ -650,6 +645,14 @@ module ActiveRecord
 
       def belongs_to?; true; end
 
+      def association_class
+        if polymorphic?
+          Associations::BelongsToPolymorphicAssociation
+        else
+          Associations::BelongsToAssociation
+        end
+      end
+
       def join_keys(association_klass)
         key = polymorphic? ? association_primary_key(association_klass) : association_primary_key
         JoinKeys.new(key, foreign_key)