If a counter_cache is defined, then using update_attributes and changing

the primary key on an association will make sure that the corresponding
counter on the association is changed properly. Fixes #9722.

1 files changed, 26 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index a8151cd23e..79ca34d89d 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,31 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Counter caches on associations will now stay valid when attributes are
+    updated (not just when records are created or destroyed), for example,
+    when calling +update_attributes+. The following code now works:
+
+      class Comment < ActiveRecord::Base
+        belongs_to :post, counter_cache: true
+      end
+
+      class Post < ActiveRecord::Base
+        has_many :comments
+      end
+
+      post = Post.create
+      comment = Comment.create
+
+      post.comments << comment
+      post.save.reload.comments_count     # => 1
+      comment.update_attributes(:post_id => nil)
+
+      post.save.reload.comments_count     # => 0
+
+    Updating the id of a +belongs_to+ object with the id of a new object will
+    also keep the count accurate.
+
+    *John Wang*
+
 *   Referencing join tables implicitly was deprecated. There is a
     possibility that these deprecation warnings are shown even if you
     don't make use of that feature. You can now disable the feature entirely.