Add collection cache versioning

Cache versioning enables the same cache key to be reused when the object
being cached changes by moving the volatile part of the cache key out of
the cache key and into a version that is embedded in the cache entry.

This is already occurring when the object being cached is an
`ActiveRecord::Base`, but when caching an `ActiveRecord::Relation`
we are currently still putting the volatile information (max updated at
and count) as part of the cache key.

This PR moves the volatile part of the relations `cache_key` into the
`cache_version` to support recycling cache keys for
`ActiveRecord::Relation`s.

1 files changed, 34 insertions, 0 deletions

diff --git a/activerecord/test/cases/collection_cache_key_test.rb b/activerecord/test/cases/collection_cache_key_test.rb
index 483383257b..f07f3c42e6 100644
--- a/activerecord/test/cases/collection_cache_key_test.rb
+++ b/activerecord/test/cases/collection_cache_key_test.rb
@@ -171,5 +171,39 @@ module ActiveRecord
 
       assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
     end
+
+    test "cache_key should be stable when using collection_cache_versioning" do
+      with_collection_cache_versioning do
+        developers = Developer.where(salary: 100000)
+
+        assert_match(/\Adevelopers\/query-(\h+)\z/, developers.cache_key)
+
+        /\Adevelopers\/query-(\h+)\z/ =~ developers.cache_key
+
+        assert_equal ActiveSupport::Digest.hexdigest(developers.to_sql), $1
+      end
+    end
+
+    test "cache_version for relation" do
+      with_collection_cache_versioning do
+        developers = Developer.where(salary: 100000).order(updated_at: :desc)
+        last_developer_timestamp = developers.first.updated_at
+
+        assert_match(/(\d+)-(\d+)\z/, developers.cache_version)
+
+        /(\d+)-(\d+)\z/ =~ developers.cache_version
+
+        assert_equal developers.count.to_s, $1
+        assert_equal last_developer_timestamp.to_s(ActiveRecord::Base.cache_timestamp_format), $2
+      end
+    end
+
+    def with_collection_cache_versioning(value = true)
+      @old_collection_cache_versioning = ActiveRecord::Base.collection_cache_versioning
+      ActiveRecord::Base.collection_cache_versioning = value
+      yield
+    ensure
+      ActiveRecord::Base.collection_cache_versioning = @old_collection_cache_versioning
+    end
   end
 end