Merge pull request #9252 from senny/8423_hmt_preloading_bug

don't cache invalid subsets when preloading hmt associations

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Preloading `has_many :through` associations with conditions won't
+    cache the `:through` association. This will prevent invalid
+    subsets to be cached.
+    Fixes #8423.
+
+    Example:
+
+        class User
+          has_many :posts
+          has_many :recent_comments, -> { where('created_at > ?', 1.week.ago) }, :through => :posts
+        end
+
+        a_user = User.includes(:recent_comments).first
+
+        # this is preloaded
+        a_user.recent_comments
+
+        # fetching the recent_comments through the posts association won't preload it.
+        a_user.posts
+
+    *Yves Senn*
+
 *   Don't run after_commit callback when creating through an association
     if saving the record fails.
 

activerecord/lib/active_record/associations/preloader/through_association.rb

@@ -31,7 +31,8 @@ def through_records_by_owner
             through_records = Array.wrap(owner.send(through_reflection.name))
 
             # Dont cache the association - we would only be caching a subset
-            if reflection.options[:source_type] && through_reflection.collection?
+            if (through_scope != through_reflection.klass.unscoped) ||
+               (reflection.options[:source_type] && through_reflection.collection?)
               owner.association(through_reflection.name).reset
             end
 

activerecord/test/cases/associations/eager_test.rb

@@ -1162,4 +1162,10 @@ def test_deep_including_through_habtm
       Post.where('1 = 0').scoping { Comment.preload(:post).find(1).post }
     )
   end
+
+  test "preloading does not cache has many association subset when preloaded with a through association" do
+    author = Author.includes(:comments_with_order_and_conditions, :posts).first
+    assert_no_queries { assert_equal 2, author.comments_with_order_and_conditions.size }
+    assert_no_queries { assert_equal 5, author.posts.size, "should not cache a subset of the association" }
+  end
 end