Use ActiveSupport::Cache.expand_cache_key for cache key expansions

lib/active_model/serializer/caching.rb

@@ -263,7 +263,11 @@ def cache_key(adapter_instance)
         parts << object_cache_key
         parts << adapter_instance.cache_key
         parts << serializer_class._cache_digest unless serializer_class._skip_digest?
-        @cache_key = parts.join('/')
+        @cache_key = expand_cache_key(parts)
+      end
+
+      def expand_cache_key(parts)
+        ActiveSupport::Cache.expand_cache_key(parts)
       end
 
       # Use object's cache_key if available, else derive a key from the object

test/cache_test.rb

@@ -4,6 +4,26 @@
 
 module ActiveModelSerializers
   class CacheTest < ActiveSupport::TestCase
+    class AuthorWithCustomCacheKey < Author
+      class DerivedCacheKey
+        def initialize(object, method)
+          @object = object
+          @method = method
+        end
+
+        def cache_key
+          @object.__send__(@method)
+        end
+      end
+
+      def cache_key
+        [
+          DerivedCacheKey.new(self, :name),
+          DerivedCacheKey.new(self, :id)
+        ]
+      end
+    end
+
     class UncachedAuthor < Author
       # To confirm cache_key is set using updated_at and cache_key option passed to cache
       undef_method :cache_key
@@ -106,6 +126,22 @@ def test_cache_key_interpolation_with_updated_at_when_cache_key_is_not_defined_o
       assert_equal(uncached_author_serializer.attributes.to_json, cache_store.fetch(key).to_json)
     end
 
+    def test_cache_key_with_non_primitive_values
+      author = AuthorWithCustomCacheKey.new(id: 10, name: "hello")
+      same_author = AuthorWithCustomCacheKey.new(id: 10, name: "hello")
+      diff_author = AuthorWithCustomCacheKey.new(id: 11, name: "hello")
+
+      author_serializer = AuthorSerializer.new(author)
+      same_author_serializer = AuthorSerializer.new(same_author)
+      diff_author_serializer = AuthorSerializer.new(diff_author)
+      adapter = AuthorSerializer.serialization_adapter_instance
+
+      assert_equal(author_serializer.cache_key(adapter),
+                   same_author_serializer.cache_key(adapter))
+      refute_equal(author_serializer.cache_key(adapter),
+                   diff_author_serializer.cache_key(adapter))
+    end
+
     def test_default_cache_key_fallback
       render_object_with_cache(@comment)
       key = "#{@comment.cache_key}/#{adapter.cache_key}"