push constructable? on to the reflection

activerecord/lib/active_record/associations/builder/association.rb

@@ -31,7 +31,7 @@ def self.build(model, name, scope, options, &block)
 
       builder = new(name, scope, options, &block)
       reflection = builder.build(model)
-      builder.define_accessors model
+      builder.define_accessors model, reflection
       builder.define_callbacks model, reflection
       builder.define_extensions model
       reflection
@@ -82,7 +82,7 @@ def define_callbacks(model, reflection)
     #
     # Post.first.comments and Post.first.comments= methods are defined by this method...
 
-    def define_accessors(model)
+    def define_accessors(model, reflection)
       mixin = model.generated_feature_methods
       define_readers(mixin)
       define_writers(mixin)

activerecord/lib/active_record/associations/builder/belongs_to.rb

@@ -8,10 +8,6 @@ def valid_options
       super + [:foreign_type, :polymorphic, :touch]
     end
 
-    def constructable?
-      !options[:polymorphic]
-    end
-
     def valid_dependent_options
       [:destroy, :delete]
     end
@@ -22,7 +18,7 @@ def define_callbacks(model, reflection)
       add_touch_callbacks(model, reflection)         if options[:touch]
     end
 
-    def define_accessors(mixin)
+    def define_accessors(mixin, reflection)
       super
       add_counter_cache_methods mixin
     end
@@ -58,7 +54,7 @@ def belongs_to_counter_cache_after_update(association, reflection)
 
           if (@_after_create_counter_called ||= false)
             @_after_create_counter_called = false
-          elsif attribute_changed?(foreign_key) && !new_record? && association.constructable?
+          elsif attribute_changed?(foreign_key) && !new_record? && reflection.constructable?
             model           = reflection.klass
             foreign_key_was = attribute_was foreign_key
             foreign_key     = attribute foreign_key

activerecord/lib/active_record/associations/builder/has_one.rb

@@ -10,10 +10,6 @@ def valid_options
       valid
     end
 
-    def constructable?
-      !options[:through]
-    end
-
     def valid_dependent_options
       [:destroy, :delete, :nullify, :restrict_with_error, :restrict_with_exception]
     end

activerecord/lib/active_record/associations/builder/singular_association.rb

@@ -6,13 +6,9 @@ def valid_options
       super + [:remote, :dependent, :counter_cache, :primary_key, :inverse_of]
     end
 
-    def constructable?
-      true
-    end
-
-    def define_accessors(model)
+    def define_accessors(model, reflection)
       super
-      define_constructors(model.generated_feature_methods) if constructable?
+      define_constructors(model.generated_feature_methods) if reflection.constructable?
     end
 
     # Defines the (build|create)_association methods for belongs_to or has_one association

activerecord/lib/active_record/reflection.rb

@@ -200,6 +200,7 @@ def initialize(macro, name, scope, options, active_record)
         @automatic_inverse_of = nil
         @type         = options[:as] && "#{options[:as]}_type"
         @foreign_type = options[:foreign_type] || "#{name}_type"
+        @constructable = calculate_constructable(macro, options)
       end
 
       # Returns a new, unsaved instance of the associated class. +attributes+ will
@@ -208,6 +209,10 @@ def build_association(attributes, &block)
         klass.new(attributes, &block)
       end
 
+      def constructable? # :nodoc:
+        @constructable
+      end
+
       def table_name
         klass.table_name
       end
@@ -379,6 +384,17 @@ def actual_source_reflection # FIXME: this is a horrible name
       end
 
       private
+      def calculate_constructable(macro, options)
+        case macro
+        when :belongs_to
+          !options[:polymorphic]
+        when :has_one
+          !options[:through]
+        else
+          true
+        end
+      end
+
         # Attempts to find the inverse association name automatically.
         # If it cannot find a suitable inverse association name, it returns
         # nil.