2 files changed, 13 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/associations/association_collection.rb b/activerecord/lib/active_record/associations/association_collection.rb
index 91e0a9f2f8..cb2d9e0a79 100644
--- a/activerecord/lib/active_record/associations/association_collection.rb
+++ b/activerecord/lib/active_record/associations/association_collection.rb
@@ -363,6 +363,7 @@ module ActiveRecord
 
       def include?(record)
         return false unless record.is_a?(@reflection.klass)
+        return include_in_memory?(record) if record.new_record?
         load_target if @reflection.options[:finder_sql] && !loaded?
         return @target.include?(record) if loaded?
         exists?(record)
@@ -554,6 +555,17 @@ module ActiveRecord
           args.first.kind_of?(Hash) || !(loaded? || @owner.new_record? || @reflection.options[:finder_sql] ||
                                          @target.any? { |record| record.new_record? } || args.first.kind_of?(Integer))
         end
+
+        def include_in_memory?(record)
+          if @reflection.is_a?(ActiveRecord::Reflection::ThroughReflection)
+            @owner.send(proxy_reflection.through_reflection.name.to_sym).any? do |source|
+              target = source.send(proxy_reflection.source_reflection.name)
+              target.respond_to?(:include?) ? target.include?(record) : target == record
+            end
+          else
+            @target.include?(record)
+          end
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
index 38454ec242..e429806b0c 100644
--- a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
@@ -39,7 +39,7 @@ module ActiveRecord
         def set_inverse_instance(record, instance)
           return if record.nil? || !we_can_set_the_inverse_on_this?(record)
           inverse_relationship = @reflection.polymorphic_inverse_of(record.class)
-          unless inverse_relationship.nil?
+          if inverse_relationship
             record.send(:"set_#{inverse_relationship.name}_target", instance)
           end
         end