Fix belongs_to polymorphic with custom primary key on target.

Closes #3104.

1 files changed, 11 insertions, 15 deletions

diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 89179779e3..1929a808ed 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -211,11 +211,9 @@ module ActiveRecord
         @association_foreign_key ||= options[:association_foreign_key] || class_name.foreign_key
       end
 
-      def association_primary_key
-        @association_primary_key ||=
-          options[:primary_key] ||
-          !options[:polymorphic] && klass.primary_key ||
-          'id'
+      # klass option is necessary to support loading polymorphic associations
+      def association_primary_key(klass = self.klass)
+        options[:primary_key] || klass.primary_key
       end
 
       def active_record_primary_key
@@ -463,17 +461,15 @@ module ActiveRecord
       # We want to use the klass from this reflection, rather than just delegate straight to
       # the source_reflection, because the source_reflection may be polymorphic. We still
       # need to respect the source_reflection's :primary_key option, though.
-      def association_primary_key
-        @association_primary_key ||= begin
-          # Get the "actual" source reflection if the immediate source reflection has a
-          # source reflection itself
-          source_reflection = self.source_reflection
-          while source_reflection.source_reflection
-            source_reflection = source_reflection.source_reflection
-          end
-
-          source_reflection.options[:primary_key] || klass.primary_key
+      def association_primary_key(klass = self.klass)
+        # Get the "actual" source reflection if the immediate source reflection has a
+        # source reflection itself
+        source_reflection = self.source_reflection
+        while source_reflection.source_reflection
+          source_reflection = source_reflection.source_reflection
         end
+
+        source_reflection.options[:primary_key] || klass.primary_key
       end
 
       # Gets an array of possible <tt>:through</tt> source reflection names: