Fix stale state for composite foreign keys in belongs_to association

activerecord/lib/active_record/associations/belongs_to_association.rb

@@ -148,8 +148,11 @@ def invertible_for?(record)
         end
 
         def stale_state
-          result = owner._read_attribute(reflection.foreign_key) { |n| owner.send(:missing_attribute, n, caller) }
-          result && result.to_s
+          result = Array(reflection.foreign_key).map do |fk|
+            owner._read_attribute(fk) { |n| owner.send(:missing_attribute, n, caller) }
+          end.join(",")
+
+          result.empty? ? nil : result
         end
     end
   end

activerecord/test/cases/associations/belongs_to_associations_test.rb

@@ -31,6 +31,9 @@
 require "models/node"
 require "models/club"
 require "models/cpk"
+require "models/sharded/blog"
+require "models/sharded/blog_post"
+require "models/sharded/comment"
 
 class BelongsToAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :developers, :projects, :topics,
@@ -392,6 +395,18 @@ def test_should_set_composite_foreign_key_on_association_when_key_changes_on_ass
     assert_equal 3, book.shop_id
   end
 
+  def test_should_reload_association_on_model_with_query_constraints_when_foreign_key_changes
+    blog = Sharded::Blog.create!
+    blog_post = Sharded::BlogPost.create!(blog: blog)
+    comment = Sharded::Comment.create!(blog: blog)
+
+    # Load the association once
+    comment.blog_post
+    comment.blog_post_id = blog_post.id
+
+    assert_equal blog_post, comment.blog_post
+  end
+
   def test_building_the_belonging_object_with_implicit_sti_base_class
     account = Account.new
     company = account.build_firm