1 files changed, 16 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index f47282b7fd..263ba922da 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -200,6 +200,7 @@ module ActiveRecord
         @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 @@ module ActiveRecord
         klass.new(attributes, &block)
       end
 
+      def constructable? # :nodoc:
+        @constructable
+      end
+
       def table_name
         klass.table_name
       end
@@ -379,6 +384,17 @@ module ActiveRecord
       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.