1 files changed, 40 insertions, 32 deletions
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 37e18626b5..823ca1f54f 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]
@@ -522,14 +501,7 @@ module ActiveRecord
       private
 
         def calculate_constructable(macro, options)
-          case macro
-          when :belongs_to
-            !polymorphic?
-          when :has_one
-            !options[:through]
-          else
-            true
-          end
+          true
         end
 
         # Attempts to find the inverse association name automatically.
@@ -629,6 +601,14 @@ 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 +619,20 @@ 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
+
+      private
+
+        def calculate_constructable(macro, options)
+          !options[:through]
+        end
     end
 
     class BelongsToReflection < AssociationReflection # :nodoc:
@@ -650,6 +644,14 @@ 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)
@@ -658,6 +660,12 @@ module ActiveRecord
       def join_id_for(owner) # :nodoc:
         owner[foreign_key]
       end
+
+      private
+
+        def calculate_constructable(macro, options)
+          !polymorphic?
+        end
     end
 
     class HasAndBelongsToManyReflection < AssociationReflection # :nodoc: